CSY/reowolf Changeset - b6805cfb30e1 · Centrum Wiskunde & Informatica (CWI)

Changeset - b6805cfb30e1

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mh - 3 years ago 2022-02-16 16:50:38
contact@maxhenger.nl

WIP: Refactor typing pass to simplify adding expr types

1 file changed with 385 insertions and 182 deletions:

src/protocol/parser/pass_typing.rs

385

182

0 comments (0 inline, 0 general)

src/protocol/parser/pass_typing.rs

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@@ @@ -816,84 +816,182 @@ enum DefinitionType{ @@
     Function(FunctionDefinitionId),
+}
 impl DefinitionType {
     fn definition_id(&self) -> DefinitionId {
         match self {
             DefinitionType::Component(v) => v.upcast(),
             DefinitionType::Function(v) => v.upcast(),
+        }
+    }
+}
 pub(crate) struct ResolveQueueElement {
     // Note that using the `definition_id` and the `monomorph_idx` one may
     // query the type table for the full procedure type, thereby retrieving
     // the polymorphic arguments to the procedure.
     pub(crate) root_id: RootId,
     pub(crate) definition_id: DefinitionId,
     pub(crate) reserved_type_id: TypeId,
+}
 pub(crate) type ResolveQueue = Vec<ResolveQueueElement>;
 #[derive(Clone)]
-struct InferenceExpression {
+struct InferenceNode {
     expr_type: InferenceType,       // result type from expression
     expr_id: ExpressionId,          // expression that is evaluated
     inference_rule: InferenceRule,
     field_or_monomorph_idx: i32,    // index of field
     extra_data_idx: i32,            // index of extra data needed for inference
     type_id: TypeId,                // when applicable indexes into type table
+}
-impl Default for InferenceExpression {
+impl Default for InferenceNode {
     fn default() -> Self {
         Self{
             expr_type: InferenceType::default(),
             expr_id: ExpressionId::new_invalid(),
             inference_rule: InferenceRule::Noop,
             field_or_monomorph_idx: -1,
             extra_data_idx: -1,
             type_id: TypeId::new_invalid(),
+        }
+    }
+}
 /// Inferencing rule to apply. Some of these are reasonably generic. Other ones
 /// require so much custom logic that we'll not try to come up with an
 /// abstraction.
 enum InferenceRule {
     Noop,
     MonoTemplate(InferenceRuleTemplate),
     BiEqual(InferenceRuleBiEqual),
     TriEqualArgs(InferenceRuleTriEqualArgs),
     TriEqualAll(InferenceRuleTriEqualAll),
     Concatenate(InferenceRuleTwoArgs),
     IndexingExpr(InferenceRuleIndexingExpr),
     SlicingExpr(InferenceRuleSlicingExpr),
     SelectExpr(InferenceRuleSelectExpr),
     LiteralStruct,
     LiteralEnum,
     LiteralUnion,
     LiteralArray,
     LiteralTuple,
     CastExpr,
     CallExpr,
     VariableExpr,
+}
 struct InferenceRuleTemplate {
     template: &'static [InferenceTypePart],
     application: InferenceRuleTemplateApplication,
+}
 impl InferenceRuleTemplate {
     fn new_none() -> Self {
         return Self{
             template: &[],
             application: InferenceRuleTemplateApplication::None,
         };
+    }
     fn new_forced(template: &'static [InferenceTypePart]) -> Self {
         return Self{
             template,
             application: InferenceRuleTemplateApplication::Forced,
         };
+    }
     fn new_template(template: &'static [InferenceTypePart]) -> Self {
         return Self{
             template,
             application: InferenceRuleTemplateApplication::Template,
+        }
+    }
+}
 enum InferenceRuleTemplateApplication {
     None, // do not apply template, silly, but saves some bytes
     Forced,
     Template,
+}
 struct InferenceRuleBiEqual {
     template: InferenceRuleTemplate,
     argument_index: InferIndex,
+}
 struct InferenceRuleTriEqualArgs {
     argument_template: InferenceRuleTemplate,
     result_template: InferenceRuleTemplate,
     argument1_index: InferIndex,
     argument2_index: InferIndex,
+}
 struct InferenceRuleTriEqualAll {
     template: InferenceRuleTemplate,
     argument1_index: InferIndex,
     argument2_index: InferIndex,
+}
 // generic two-argument (excluding expression itself) inference rule arguments
 struct InferenceRuleTwoArgs {
     argument1_index: InferIndex,
     argument2_index: InferIndex,
+}
 struct InferenceRuleIndexingExpr {
     subject_index: InferIndex,
     index_index: InferIndex,
+}
 struct InferenceRuleSlicingExpr {
     subject_index: InferIndex,
     from_index: InferIndex,
     to_index: InferIndex,
+}
 struct InferenceRuleSelectExpr {
     subject_index: InferIndex,
+}
 /// This particular visitor will recurse depth-first into the AST and ensures
 /// that all expressions have the appropriate types.
 pub(crate) struct PassTyping {
     // Current definition we're typechecking.
     reserved_type_id: TypeId,
     definition_type: DefinitionType,
     poly_vars: Vec<ConcreteType>,
     // Buffers for iteration over various types
     var_buffer: ScopedBuffer<VariableId>,
     expr_buffer: ScopedBuffer<ExpressionId>,
     stmt_buffer: ScopedBuffer<StatementId>,
     bool_buffer: ScopedBuffer<bool>,
     // Mapping from parser type to inferred type. We attempt to continue to
     // specify these types until we're stuck or we've fully determined the type.
     var_types: HashMap<VariableId, VarData>,            // types of variables
-    expr_types: Vec<InferenceExpression>,                     // will be transferred to type table at end
+    infer_nodes: Vec<InferenceNode>,                     // will be transferred to type table at end
     extra_data: Vec<ExtraData>,       // data for polymorph inference
     // Keeping track of which expressions need to be reinferred because the
     // expressions they're linked to made progression on an associated type
     expr_queued: DequeSet<i32>,
+}
 // TODO: @Rename, this is used for a lot of type inferencing. It seems like
 //  there is a different underlying architecture waiting to surface.
 struct ExtraData {
     expr_id: ExpressionId, // the expression with which this data is associated
     definition_id: DefinitionId, // the definition, only used for user feedback
     /// Progression of polymorphic variables (if any)
     poly_vars: Vec<InferenceType>,
     /// Progression of types of call arguments or struct members
     embedded: Vec<InferenceType>,
     returned: InferenceType,
+}
 impl Default for ExtraData {
     fn default() -> Self {
         Self{
             expr_id: ExpressionId::new_invalid(),
             definition_id: DefinitionId::new_invalid(),
             poly_vars: Vec::new(),
@@ @@ -912,49 +1010,49 @@ struct VarData { @@
     /// channel's interior type is resolved, we can also resolve the other one.
     linked_var: Option<VariableId>,
+}
 impl VarData {
     fn new_channel(var_type: InferenceType, other_port: VariableId) -> Self {
         Self{ var_type, used_at: Vec::new(), linked_var: Some(other_port) }
+    }
     fn new_local(var_type: InferenceType) -> Self {
         Self{ var_type, used_at: Vec::new(), linked_var: None }
+    }
+}
 impl PassTyping {
     pub(crate) fn new() -> Self {
         PassTyping {
             reserved_type_id: TypeId::new_invalid(),
             definition_type: DefinitionType::Function(FunctionDefinitionId::new_invalid()),
             poly_vars: Vec::new(),
             var_buffer: ScopedBuffer::with_capacity(BUFFER_INIT_CAP_LARGE),
             expr_buffer: ScopedBuffer::with_capacity(BUFFER_INIT_CAP_LARGE),
             stmt_buffer: ScopedBuffer::with_capacity(BUFFER_INIT_CAP_LARGE),
             bool_buffer: ScopedBuffer::with_capacity(BUFFER_INIT_CAP_SMALL),
             var_types: HashMap::new(),
-            expr_types: Vec::new(),
+            infer_nodes: Vec::new(),
             extra_data: Vec::new(),
             expr_queued: DequeSet::new(),
+        }
+    }
     pub(crate) fn queue_module_definitions(ctx: &mut Ctx, queue: &mut ResolveQueue) {
         debug_assert_eq!(ctx.module().phase, ModuleCompilationPhase::ValidatedAndLinked);
         let root_id = ctx.module().root_id;
         let root = &ctx.heap.protocol_descriptions[root_id];
         for definition_id in &root.definitions {
             let definition = &ctx.heap[*definition_id];
             let first_concrete_part = match definition {
                 Definition::Function(definition) => {
                     if definition.poly_vars.is_empty() {
                         Some(ConcreteTypePart::Function(*definition_id, 0))
                     } else {
                         None
+                    }
+                }
                 Definition::Component(definition) => {
                     if definition.poly_vars.is_empty() {
                         Some(ConcreteTypePart::Component(*definition_id, 0))
                     } else {
@@ @@ -985,125 +1083,125 @@ impl PassTyping { @@
         // Prepare for visiting the definition
         self.reserved_type_id = element.reserved_type_id;
         let proc_base = ctx.types.get_base_definition(&element.definition_id).unwrap();
         if proc_base.is_polymorph {
             let monomorph = ctx.types.get_monomorph(element.reserved_type_id);
             for poly_arg in monomorph.concrete_type.embedded_iter(0) {
                 self.poly_vars.push(ConcreteType{ parts: Vec::from(poly_arg) });
+            }
+        }
         // Visit the definition, setting up the type resolving process, then
         // (attempt to) resolve all types
         self.visit_definition(ctx, element.definition_id)?;
         self.resolve_types(ctx, queue)?;
         Ok(())
+    }
     fn reset(&mut self) {
         self.reserved_type_id = TypeId::new_invalid();
         self.definition_type = DefinitionType::Function(FunctionDefinitionId::new_invalid());
         self.poly_vars.clear();
         self.var_types.clear();
-        self.expr_types.clear();
+        self.infer_nodes.clear();
         self.extra_data.clear();
         self.expr_queued.clear();
+    }
+}
 // -----------------------------------------------------------------------------
 // PassTyping - Visitor-like implementation
 // -----------------------------------------------------------------------------
 type VisitorResult = Result<(), ParseError>;
-type VisitStmtResult = Result<>
+type VisitExprResult = Result<InferIndex, ParseError>;
 impl PassTyping {
     // Definitions
     fn visit_definition(&mut self, ctx: &mut Ctx, id: DefinitionId) -> VisitorResult {
         return visitor_recursive_definition_impl!(self, &ctx.heap[id], ctx);
+    }
     fn visit_enum_definition(&mut self, _: &mut Ctx, _: EnumDefinitionId) -> VisitorResult { return Ok(()) }
     fn visit_struct_definition(&mut self, _: &mut Ctx, _: StructDefinitionId) -> VisitorResult { return Ok(()) }
     fn visit_union_definition(&mut self, _: &mut Ctx, _: UnionDefinitionId) -> VisitorResult { return Ok(()) }
     fn visit_component_definition(&mut self, ctx: &mut Ctx, id: ComponentDefinitionId) -> VisitorResult {
         self.definition_type = DefinitionType::Component(id);
         let comp_def = &ctx.heap[id];
         debug_assert_eq!(comp_def.poly_vars.len(), self.poly_vars.len(), "component polyvars do not match imposed polyvars");
         debug_log!("{}", "-".repeat(50));
         debug_log!("Visiting component '{}': {}", comp_def.identifier.value.as_str(), id.0.index);
         debug_log!("{}", "-".repeat(50));
         // Reserve data for expression types
         debug_assert!(self.expr_types.is_empty());
         self.expr_types.resize(comp_def.num_expressions_in_body as usize, Default::default());
         debug_assert!(self.infer_nodes.is_empty());
         self.infer_nodes.resize(comp_def.num_expressions_in_body as usize, Default::default());
         // Visit parameters
         let section = self.var_buffer.start_section_initialized(comp_def.parameters.as_slice());
         for param_id in section.iter_copied() {
             let param = &ctx.heap[param_id];
             let var_type = self.determine_inference_type_from_parser_type_elements(&param.parser_type.elements, true);
             debug_assert!(var_type.is_done, "expected component arguments to be concrete types");
             self.var_types.insert(param_id, VarData::new_local(var_type));
+        }
         section.forget();
         // Visit the body and all of its expressions
         let body_stmt_id = ctx.heap[id].body;
         self.visit_block_stmt(ctx, body_stmt_id)
+    }
     fn visit_function_definition(&mut self, ctx: &mut Ctx, id: FunctionDefinitionId) -> VisitorResult {
         self.definition_type = DefinitionType::Function(id);
         let func_def = &ctx.heap[id];
         debug_assert_eq!(func_def.poly_vars.len(), self.poly_vars.len(), "function polyvars do not match imposed polyvars");
         debug_log!("{}", "-".repeat(50));
         debug_log!("Visiting function '{}': {}", func_def.identifier.value.as_str(), id.0.index);
         if debug_log_enabled!() {
             debug_log!("Polymorphic variables:");
             for (_idx, poly_var) in self.poly_vars.iter().enumerate() {
                 let mut infer_type_parts = Vec::new();
                 Self::determine_inference_type_from_concrete_type(
                     &mut infer_type_parts, &poly_var.parts
                 );
                 let _infer_type = InferenceType::new(false, true, infer_type_parts);
                 debug_log!(" - [{:03}] {:?}", _idx, _infer_type.display_name(&ctx.heap));
+            }
+        }
         debug_log!("{}", "-".repeat(50));
         // Reserve data for expression types
         debug_assert!(self.expr_types.is_empty());
         self.expr_types.resize(func_def.num_expressions_in_body as usize, Default::default());
         debug_assert!(self.infer_nodes.is_empty());
         self.infer_nodes.resize(func_def.num_expressions_in_body as usize, Default::default());
         // Visit parameters
         let section = self.var_buffer.start_section_initialized(func_def.parameters.as_slice());
         for param_id in section.iter_copied() {
             let param = &ctx.heap[param_id];
             let var_type = self.determine_inference_type_from_parser_type_elements(&param.parser_type.elements, true);
             debug_assert!(var_type.is_done, "expected function arguments to be concrete types");
             self.var_types.insert(param_id, VarData::new_local(var_type));
+        }
         section.forget();
         // Visit all of the expressions within the body
         let body_stmt_id = ctx.heap[id].body;
         self.visit_block_stmt(ctx, body_stmt_id)
+    }
     // Statements
     fn visit_stmt(&mut self, ctx: &mut Ctx, id: StatementId) -> VisitorResult {
         return visitor_recursive_statement_impl!(self, &ctx.heap[id], ctx, Ok(()));
+    }
     fn visit_block_stmt(&mut self, ctx: &mut Ctx, id: BlockStatementId) -> VisitorResult {
         // Transfer statements for traversal
@@ @@ -1216,324 +1314,463 @@ impl PassTyping { @@
         for case in &select_stmt.cases {
             section.push(case.guard);
             section.push(case.body);
+        }
         for case_index in 0..num_cases {
             let base_index = 2 * case_index;
             let guard_stmt_id = section[base_index    ];
             let block_stmt_id = section[base_index + 1];
             self.visit_stmt(ctx, guard_stmt_id)?;
             self.visit_stmt(ctx, block_stmt_id)?;
+        }
         section.forget();
         Ok(())
+    }
     fn visit_return_stmt(&mut self, ctx: &mut Ctx, id: ReturnStatementId) -> VisitorResult {
         let return_stmt = &ctx.heap[id];
         debug_assert_eq!(return_stmt.expressions.len(), 1);
         let expr_id = return_stmt.expressions[0];
         self.visit_expr(ctx, expr_id)
         self.visit_expr(ctx, expr_id)?;
         return Ok(());
+    }
     fn visit_goto_stmt(&mut self, _: &mut Ctx, _: GotoStatementId) -> VisitorResult { return Ok(()) }
     fn visit_new_stmt(&mut self, ctx: &mut Ctx, id: NewStatementId) -> VisitorResult {
         let new_stmt = &ctx.heap[id];
         let call_expr_id = new_stmt.expression;
         self.visit_call_expr(ctx, call_expr_id)
         self.visit_call_expr(ctx, call_expr_id)?;
         return Ok(());
+    }
     fn visit_expr_stmt(&mut self, ctx: &mut Ctx, id: ExpressionStatementId) -> VisitorResult {
         let expr_stmt = &ctx.heap[id];
         let subexpr_id = expr_stmt.expression;
         self.visit_expr(ctx, subexpr_id)
         self.visit_expr(ctx, subexpr_id)?;
         return Ok(());
+    }
     // Expressions
-    fn visit_expr(&mut self, ctx: &mut Ctx, id: ExpressionId) -> VisitorResult {
+    fn visit_expr(&mut self, ctx: &mut Ctx, id: ExpressionId) -> VisitExprResult {
         return visitor_recursive_expression_impl!(self, &ctx.heap[id], ctx);
+    }
     fn visit_assignment_expr(&mut self, ctx: &mut Ctx, id: AssignmentExpressionId) -> VisitorResult {
     fn visit_assignment_expr(&mut self, ctx: &mut Ctx, id: AssignmentExpressionId) -> VisitExprResult {
         use AssignmentOperator as AO;
         let upcast_id = id.upcast();
         self.insert_initial_expr_inference_type(ctx, upcast_id)?;
+        let self_index = self.insert_initial_expr_inference_type(ctx, upcast_id)?;
         let assign_expr = &ctx.heap[id];
         let assign_op = assign_expr.operation;
         let left_expr_id = assign_expr.left;
         let right_expr_id = assign_expr.right;
         self.visit_expr(ctx, left_expr_id)?;
         self.visit_expr(ctx, right_expr_id)?;
         let left_index = self.visit_expr(ctx, left_expr_id)?;
         let right_index = self.visit_expr(ctx, right_expr_id)?;
         let node = &mut self.infer_nodes[self_index];
         let argument_template = match assign_op {
             AO::Set =>
                 InferenceRuleTemplate::new_none(),
             AO::Concatenated =>
                 InferenceRuleTemplate::new_template(&ARRAYLIKE_TEMPLATE),
             AO::Multiplied | AO::Divided | AO::Added | AO::Subtracted =>
                 InferenceRuleTemplate::new_template(&NUMBERLIKE_TEMPLATE),
             AO::Remained | AO::ShiftedLeft | AO::ShiftedRight |
             AO::BitwiseAnded | AO::BitwiseXored | AO::BitwiseOred =>
                 InferenceRuleTemplate::new_template(&INTEGERLIKE_TEMPLATE),
         };
         node.inference_rule = InferenceRule::TriEqualArgs(InferenceRuleTriEqualArgs{
             argument_template,
             result_template: InferenceRuleTemplate::new_forced(&VOID_TEMPLATE),
             argument1_index: left_index,
             argument2_index: right_index,
         });
         self.progress_assignment_expr(ctx, id)
+    }
-    fn visit_binding_expr(&mut self, ctx: &mut Ctx, id: BindingExpressionId) -> VisitorResult {
+    fn visit_binding_expr(&mut self, ctx: &mut Ctx, id: BindingExpressionId) -> VisitExprResult {
         let upcast_id = id.upcast();
         self.insert_initial_expr_inference_type(ctx, upcast_id)?;
+        let self_index = self.insert_initial_expr_inference_type(ctx, upcast_id)?;
         let binding_expr = &ctx.heap[id];
         let bound_to_id = binding_expr.bound_to;
         let bound_from_id = binding_expr.bound_from;
         self.visit_expr(ctx, bound_to_id)?;
         self.visit_expr(ctx, bound_from_id)?;
         let arg_to_index = self.visit_expr(ctx, bound_to_id)?;
         let arg_from_index = self.visit_expr(ctx, bound_from_id)?;
         let node = &mut self.infer_nodes[self_index];
         node.inference_rule = InferenceRule::TriEqualArgs(InferenceRuleTriEqualArgs{
             argument_template: InferenceRuleTemplate::new_none(),
             result_template: InferenceRuleTemplate::new_forced(&BOOL_TEMPLATE),
             argument1_index: arg_to_index,
             argument2_index: arg_from_index,
         });
         self.progress_binding_expr(ctx, id)
+    }
-    fn visit_conditional_expr(&mut self, ctx: &mut Ctx, id: ConditionalExpressionId) -> VisitorResult {
+    fn visit_conditional_expr(&mut self, ctx: &mut Ctx, id: ConditionalExpressionId) -> VisitExprResult {
         let upcast_id = id.upcast();
         self.insert_initial_expr_inference_type(ctx, upcast_id)?;
+        let self_index = self.insert_initial_expr_inference_type(ctx, upcast_id)?;
         let conditional_expr = &ctx.heap[id];
         let test_expr_id = conditional_expr.test;
         let true_expr_id = conditional_expr.true_expression;
         let false_expr_id = conditional_expr.false_expression;
         self.visit_expr(ctx, test_expr_id)?;
         self.visit_expr(ctx, true_expr_id)?;
         self.visit_expr(ctx, false_expr_id)?;
         let true_index = self.visit_expr(ctx, true_expr_id)?;
         let false_index = self.visit_expr(ctx, false_expr_id)?;
         // Note: the test to the conditional expression has already been forced
         // to the boolean type. So the only thing we need to do while progressing
         // is to apply an equal3 constraint to the arguments and the result of
         // the expression.
         let node = &mut self.infer_nodes[self_index];
         node.inference_rule = InferenceRule::TriEqualAll(InferenceRuleTriEqualAll{
             template: InferenceRuleTemplate::new_none(),
             argument1_index: true_index,
             argument2_index: false_index,
         });
         self.progress_conditional_expr(ctx, id)
+    }
     fn visit_binary_expr(&mut self, ctx: &mut Ctx, id: BinaryExpressionId) -> VisitorResult {
     fn visit_binary_expr(&mut self, ctx: &mut Ctx, id: BinaryExpressionId) -> VisitExprResult {
         use BinaryOperator as BO;
         let upcast_id = id.upcast();
         self.insert_initial_expr_inference_type(ctx, upcast_id)?;
+        let self_index = self.insert_initial_expr_inference_type(ctx, upcast_id)?;
         let binary_expr = &ctx.heap[id];
         let binary_op = binary_expr.operation;
         let lhs_expr_id = binary_expr.left;
         let rhs_expr_id = binary_expr.right;
         self.visit_expr(ctx, lhs_expr_id)?;
         self.visit_expr(ctx, rhs_expr_id)?;
         let left_index = self.visit_expr(ctx, lhs_expr_id)?;
         let right_index = self.visit_expr(ctx, rhs_expr_id)?;
         let inference_rule = match binary_op {
             BO::Concatenate =>
                 InferenceRule::Concatenate(InferenceRuleTwoArgs{
                     argument1_index: left_index,
                     argument2_index: right_index,
                 }),
             BO::LogicalAnd | BO::LogicalOr =>
                 InferenceRule::TriEqualAll(InferenceRuleTriEqualAll{
                     template: InferenceRuleTemplate::new_forced(&BOOL_TEMPLATE),
                     argument1_index: left_index,
                     argument2_index: right_index,
                 }),
             BO::BitwiseOr | BO::BitwiseXor | BO::BitwiseAnd | BO::Remainder | BO::ShiftLeft | BO::ShiftRight =>
                 InferenceRule::TriEqualAll(InferenceRuleTriEqualAll{
                     template: InferenceRuleTemplate::new_template(&INTEGERLIKE_TEMPLATE),
                     argument1_index: left_index,
                     argument2_index: right_index,
                 }),
             BO::Equality | BO::Inequality =>
                 InferenceRule::TriEqualArgs(InferenceRuleTriEqualArgs{
                     argument_template: InferenceRuleTemplate::new_none(),
                     result_template: InferenceRuleTemplate::new_forced(&BOOL_TEMPLATE),
                     argument1_index: left_index,
                     argument2_index: right_index,
                 }),
             BO::LessThan | BO::GreaterThan | BO::LessThanEqual | BO::GreaterThanEqual =>
                 InferenceRule::TriEqualArgs(InferenceRuleTriEqualArgs{
                     argument_template: InferenceRuleTemplate::new_template(&NUMBERLIKE_TEMPLATE),
                     result_template: InferenceRuleTemplate::new_forced(&BOOL_TEMPLATE),
                     argument1_index: left_index,
                     argument2_index: right_index,
                 }),
             BO::Add | BO::Subtract | BO::Multiply | BO::Divide =>
                 InferenceRule::TriEqualAll(InferenceRuleTriEqualAll{
                     template: InferenceRuleTemplate::new_template(&NUMBERLIKE_TEMPLATE),
                     argument1_index: left_index,
                     argument2_index: right_index,
                 }),
         };
         let node = &mut self.infer_nodes[self_index];
         node.inference_rule = inference_rule;
         self.progress_binary_expr(ctx, id)
+    }
     fn visit_unary_expr(&mut self, ctx: &mut Ctx, id: UnaryExpressionId) -> VisitorResult {
     fn visit_unary_expr(&mut self, ctx: &mut Ctx, id: UnaryExpressionId) -> VisitExprResult {
         use UnaryOperator as UO;
         let upcast_id = id.upcast();
         self.insert_initial_expr_inference_type(ctx, upcast_id)?;
+        let self_index = self.insert_initial_expr_inference_type(ctx, upcast_id)?;
         let unary_expr = &ctx.heap[id];
         let operation = unary_expr.operation;
         let arg_expr_id = unary_expr.expression;
         self.visit_expr(ctx, arg_expr_id)?;
         let argument_index = self.visit_expr(ctx, arg_expr_id)?;
         let template = match operation {
             UO::Positive | UO::Negative =>
                 InferenceRuleTemplate::new_template(&NUMBERLIKE_TEMPLATE),
             UO::BitwiseNot =>
                 InferenceRuleTemplate::new_template(&INTEGERLIKE_TEMPLATE),
             UO::LogicalNot =>
                 InferenceRuleTemplate::new_forced(&BOOL_TEMPLATE),
         };
         let node = &mut self.infer_nodes[self_index];
         node.inference_rule = InferenceRule::BiEqual(InferenceRuleBiEqual{
             template, argument_index,
         });
         self.progress_unary_expr(ctx, id)
+    }
-    fn visit_indexing_expr(&mut self, ctx: &mut Ctx, id: IndexingExpressionId) -> VisitorResult {
+    fn visit_indexing_expr(&mut self, ctx: &mut Ctx, id: IndexingExpressionId) -> VisitExprResult {
         let upcast_id = id.upcast();
         self.insert_initial_expr_inference_type(ctx, upcast_id)?;
+        let self_index = self.insert_initial_expr_inference_type(ctx, upcast_id)?;
         let indexing_expr = &ctx.heap[id];
         let subject_expr_id = indexing_expr.subject;
         let index_expr_id = indexing_expr.index;
         self.visit_expr(ctx, subject_expr_id)?;
         self.visit_expr(ctx, index_expr_id)?;
         let subject_index = self.visit_expr(ctx, subject_expr_id)?;
         let index_index = self.visit_expr(ctx, index_expr_id)?; // cool name, bro
         let node = &mut self.infer_nodes[self_index];
         node.inference_rule = InferenceRule::IndexingExpr(InferenceRuleIndexingExpr{
             subject_index, index_index,
         });
         self.progress_indexing_expr(ctx, id)
+    }
-    fn visit_slicing_expr(&mut self, ctx: &mut Ctx, id: SlicingExpressionId) -> VisitorResult {
+    fn visit_slicing_expr(&mut self, ctx: &mut Ctx, id: SlicingExpressionId) -> VisitExprResult {
         let upcast_id = id.upcast();
         self.insert_initial_expr_inference_type(ctx, upcast_id)?;
+        let self_index = self.insert_initial_expr_inference_type(ctx, upcast_id)?;
         let slicing_expr = &ctx.heap[id];
         let subject_expr_id = slicing_expr.subject;
         let from_expr_id = slicing_expr.from_index;
         let to_expr_id = slicing_expr.to_index;
         self.visit_expr(ctx, subject_expr_id)?;
         self.visit_expr(ctx, from_expr_id)?;
         self.visit_expr(ctx, to_expr_id)?;
         let subject_index = self.visit_expr(ctx, subject_expr_id)?;
         let from_index = self.visit_expr(ctx, from_expr_id)?;
         let to_index = self.visit_expr(ctx, to_expr_id)?;
         let node = &mut self.infer_nodes[self_index];
         node.inference_rule = InferenceRule::SlicingExpr(InferenceRuleSlicingExpr{
             subject_index, from_index, to_index,
         });
         self.progress_slicing_expr(ctx, id)
+    }
-    fn visit_select_expr(&mut self, ctx: &mut Ctx, id: SelectExpressionId) -> VisitorResult {
+    fn visit_select_expr(&mut self, ctx: &mut Ctx, id: SelectExpressionId) -> VisitExprResult {
         let upcast_id = id.upcast();
         self.insert_initial_expr_inference_type(ctx, upcast_id)?;
+        let self_index = self.insert_initial_expr_inference_type(ctx, upcast_id)?;
         let select_expr = &ctx.heap[id];
         let subject_expr_id = select_expr.subject;
         self.visit_expr(ctx, subject_expr_id)?;
         let subject_index = self.visit_expr(ctx, subject_expr_id)?;
         let node = &mut self.infer_nodes[self_index];
         node.inference_rule = InferenceRule::SelectExpr(InferenceRuleSelectExpr{
             subject_index,
         });
         self.progress_select_expr(ctx, id)
+    }
-    fn visit_literal_expr(&mut self, ctx: &mut Ctx, id: LiteralExpressionId) -> VisitorResult {
+    fn visit_literal_expr(&mut self, ctx: &mut Ctx, id: LiteralExpressionId) -> VisitExprResult {
         let upcast_id = id.upcast();
         self.insert_initial_expr_inference_type(ctx, upcast_id)?;
+        let self_index = self.insert_initial_expr_inference_type(ctx, upcast_id)?;
         let literal_expr = &ctx.heap[id];
         match &literal_expr.value {
             Literal::Null | Literal::False | Literal::True |
             Literal::Integer(_) | Literal::Character(_) | Literal::String(_) => {
                 // No subexpressions
             Literal::Null => {
                 let node = &mut self.infer_nodes[self_index];
                 node.inference_rule = InferenceRule::MonoTemplate(InferenceRuleTemplate::new_template(&MESSAGE_TEMPLATE));
             },
             Literal::Integer(_) => {
                 let node = &mut self.infer_nodes[self_index];
                 node.inference_rule = InferenceRule::MonoTemplate(InferenceRuleTemplate::new_template(&INTEGERLIKE_TEMPLATE));
             },
             Literal::True | Literal::False => {
                 let node = &mut self.infer_nodes[self_index];
                 node.inference_rule = InferenceRule::MonoTemplate(InferenceRuleTemplate::new_forced(&BOOL_TEMPLATE));
             },
             Literal::Character(_) => {
                 let node = &mut self.infer_nodes[self_index];
                 node.inference_rule = InferenceRule::MonoTemplate(InferenceRuleTemplate::new_forced(&CHARACTER_TEMPLATE));
             },
             Literal::String(_) => {
                 let node = &mut self.infer_nodes[self_index];
                 node.inference_rule = InferenceRule::MonoTemplate(InferenceRuleTemplate::new_forced(&STRING_TEMPLATE));
             },
             Literal::Struct(literal) => {
                 let mut expr_ids = self.expr_buffer.start_section();
                 for field in &literal.fields {
                     expr_ids.push(field.value);
+                }
                 self.insert_initial_struct_polymorph_data(ctx, id);
                 for expr_id in expr_ids.iter_copied() {
                     self.visit_expr(ctx, expr_id)?;
+                }
                 expr_ids.forget();
             },
             Literal::Enum(_) => {
                 // Enumerations do not carry any subexpressions, but may still
                 // have a user-defined polymorphic marker variable. For this
                 // reason we may still have to apply inference to this
                 // polymorphic variable
                 self.insert_initial_enum_polymorph_data(ctx, id);
             },
             Literal::Union(literal) => {
                 // May carry subexpressions and polymorphic arguments
                 let expr_ids = self.expr_buffer.start_section_initialized(literal.values.as_slice());
                 self.insert_initial_union_polymorph_data(ctx, id);
                 for expr_id in expr_ids.iter_copied() {
                     self.visit_expr(ctx, expr_id)?;
+                }
                 expr_ids.forget();
             },
             Literal::Array(expressions) | Literal::Tuple(expressions) => {
                 let expr_ids = self.expr_buffer.start_section_initialized(expressions.as_slice());
                 for expr_id in expr_ids.iter_copied() {
                     self.visit_expr(ctx, expr_id)?;
+                }
                 expr_ids.forget();
+            }
+        }
         self.progress_literal_expr(ctx, id)
+    }
-    fn visit_cast_expr(&mut self, ctx: &mut Ctx, id: CastExpressionId) -> VisitorResult {
+    fn visit_cast_expr(&mut self, ctx: &mut Ctx, id: CastExpressionId) -> VisitExprResult {
         let upcast_id = id.upcast();
         self.insert_initial_expr_inference_type(ctx, upcast_id)?;
         let cast_expr = &ctx.heap[id];
         let subject_expr_id = cast_expr.subject;
         self.visit_expr(ctx, subject_expr_id)?;
         self.progress_cast_expr(ctx, id)
+    }
-    fn visit_call_expr(&mut self, ctx: &mut Ctx, id: CallExpressionId) -> VisitorResult {
+    fn visit_call_expr(&mut self, ctx: &mut Ctx, id: CallExpressionId) -> VisitExprResult {
         let upcast_id = id.upcast();
         self.insert_initial_expr_inference_type(ctx, upcast_id)?;
         self.insert_initial_call_polymorph_data(ctx, id);
         // By default we set the polymorph idx for calls to 0. If the call ends
         // up not being a polymorphic one, then we will select the default
         // expression types in the type table
         let call_expr = &ctx.heap[id];
-        self.expr_types[call_expr.unique_id_in_definition as usize].field_or_monomorph_idx = 0;
+        self.infer_nodes[call_expr.unique_id_in_definition as usize].field_or_monomorph_idx = 0;
         // Visit all arguments
         let expr_ids = self.expr_buffer.start_section_initialized(call_expr.arguments.as_slice());
         for arg_expr_id in expr_ids.iter_copied() {
             self.visit_expr(ctx, arg_expr_id)?;
+        }
         expr_ids.forget();
         self.progress_call_expr(ctx, id)
+    }
-    fn visit_variable_expr(&mut self, ctx: &mut Ctx, id: VariableExpressionId) -> VisitorResult {
+    fn visit_variable_expr(&mut self, ctx: &mut Ctx, id: VariableExpressionId) -> VisitExprResult {
         let upcast_id = id.upcast();
         self.insert_initial_expr_inference_type(ctx, upcast_id)?;
         let var_expr = &ctx.heap[id];
         debug_assert!(var_expr.declaration.is_some());
         // Not pretty: if a binding expression, then this is the first time we
         // encounter the variable, so we still need to insert the variable data.
         let declaration = &ctx.heap[var_expr.declaration.unwrap()];
         if !self.var_types.contains_key(&declaration.this)  {
             debug_assert!(declaration.kind == VariableKind::Binding);
             let var_type = self.determine_inference_type_from_parser_type_elements(
                 &declaration.parser_type.elements, true
             );
             self.var_types.insert(declaration.this, VarData{
                 var_type,
                 used_at: vec![upcast_id],
                 linked_var: None
             });
         } else {
             let var_data = self.var_types.get_mut(&declaration.this).unwrap();
             var_data.used_at.push(upcast_id);
+        }
         self.progress_variable_expr(ctx, id)
+    }
+}
 // -----------------------------------------------------------------------------
 // PassTyping - Type-inference progression
 // -----------------------------------------------------------------------------
 impl PassTyping {
     #[allow(dead_code)] // used when debug flag at the top of this file is true.
     fn debug_get_display_name(&self, ctx: &Ctx, expr_id: ExpressionId) -> String {
         let expr_idx = ctx.heap[expr_id].get_unique_id_in_definition();
-        let expr_type = &self.expr_types[expr_idx as usize].expr_type;
+        let expr_type = &self.infer_nodes[expr_idx as usize].expr_type;
         expr_type.display_name(&ctx.heap)
+    }
     fn resolve_types(&mut self, ctx: &mut Ctx, queue: &mut ResolveQueue) -> Result<(), ParseError> {
         // Keep inferring until we can no longer make any progress
         while !self.expr_queued.is_empty() {
             // Make as much progress as possible without forced integer
             // inference.
             while !self.expr_queued.is_empty() {
                 let next_expr_idx = self.expr_queued.pop_front().unwrap();
                 self.progress_expr(ctx, next_expr_idx)?;
+            }
             // Nothing is queued anymore. However we might have integer literals
             // whose type cannot be inferred. For convenience's sake we'll
             // infer these to be s32.
-            for (infer_expr_idx, infer_expr) in self.expr_types.iter_mut().enumerate() {
+            for (infer_expr_idx, infer_expr) in self.infer_nodes.iter_mut().enumerate() {
                 let expr_type = &mut infer_expr.expr_type;
                 if !expr_type.is_done && expr_type.parts.len() == 1 && expr_type.parts[0] == InferenceTypePart::IntegerLike {
                     // Force integer type to s32
                     expr_type.parts[0] = InferenceTypePart::SInt32;
                     expr_type.is_done = true;
                     // Requeue expression (and its parent, if it exists)
                     self.expr_queued.push_back(infer_expr_idx as i32);
                     if let Some(parent_expr) = ctx.heap[infer_expr.expr_id].parent_expr_id() {
                         let parent_idx = ctx.heap[parent_expr].get_unique_id_in_definition();
                         self.expr_queued.push_back(parent_idx);
+                    }
+                }
+            }
+        }
         // Helper for transferring polymorphic variables to concrete types and
         // checking if they're completely specified
         fn inference_type_to_concrete_type(
             ctx: &Ctx, expr_id: ExpressionId, inference: &Vec<InferenceType>,
             first_concrete_part: ConcreteTypePart,
         ) -> Result<ConcreteType, ParseError> {
             // Prepare storage vector
@@ @@ -1558,49 +1795,49 @@ impl PassTyping { @@
                             Literal::Enum(lit) => lit.definition,
                             Literal::Union(lit) => lit.definition,
                             Literal::Struct(lit) => lit.definition,
                             _ => unreachable!()
                         },
                         _ => unreachable!(),
                     };
                     let poly_vars = ctx.heap[definition].poly_vars();
                     return Err(ParseError::new_error_at_span(
                         &ctx.module().source, expr.operation_span(), format!(
                             "could not fully infer the type of polymorphic variable '{}' of this expression (got '{}')",
                             poly_vars[poly_idx].value.as_str(), poly_type.display_name(&ctx.heap)
+                        )
                     ));
+                }
                 poly_type.write_concrete_type(&mut concrete_type);
+            }
             Ok(concrete_type)
+        }
         // Inference is now done. But we may still have uninferred types. So we
         // check for these.
-        for infer_expr in self.expr_types.iter_mut() {
+        for infer_expr in self.infer_nodes.iter_mut() {
             if !infer_expr.expr_type.is_done {
                 let expr = &ctx.heap[infer_expr.expr_id];
                 return Err(ParseError::new_error_at_span(
                     &ctx.module().source, expr.full_span(), format!(
                         "could not fully infer the type of this expression (got '{}')",
                         infer_expr.expr_type.display_name(&ctx.heap)
+                    )
                 ));
+            }
             // Expression is fine, check if any extra data is attached
             if infer_expr.extra_data_idx < 0 { continue; }
             // Extra data is attached, perform typechecking and transfer
             // resolved information to the expression
             let extra_data = &self.extra_data[infer_expr.extra_data_idx as usize];
             // Note that only call and literal expressions need full inference.
             // Select expressions also use `extra_data`, but only for temporary
             // storage of the struct type whose field it is selecting.
             match &ctx.heap[extra_data.expr_id] {
                 Expression::Call(expr) => {
                     // Check if it is not a builtin function. If not, then
                     // construct the first part of the concrete type.
@@ @@ -1664,64 +1901,64 @@ impl PassTyping { @@
             DefinitionType::Component(id) => {
                 let definition = &ctx.heap[*id];
                 &definition.parameters
             },
             DefinitionType::Function(id) => {
                 let definition = &ctx.heap[*id];
                 &definition.parameters
             },
         };
         let target = ctx.types.get_procedure_monomorph_mut(self.reserved_type_id);
         debug_assert!(target.arg_types.is_empty()); // makes sure we never queue a procedure's type inferencing twice
         debug_assert!(target.expr_data.is_empty());
         // - Write the arguments to the procedure
         target.arg_types.reserve(procedure_arguments.len());
         for argument_id in procedure_arguments {
             let mut concrete = ConcreteType::default();
             let argument_type = self.var_types.get(argument_id).unwrap();
             argument_type.var_type.write_concrete_type(&mut concrete);
             target.arg_types.push(concrete);
+        }
         // - Write the expression data
         target.expr_data.reserve(self.expr_types.len());
         for infer_expr in self.expr_types.iter() {
         target.expr_data.reserve(self.infer_nodes.len());
         for infer_expr in self.infer_nodes.iter() {
             let mut concrete = ConcreteType::default();
             infer_expr.expr_type.write_concrete_type(&mut concrete);
             target.expr_data.push(MonomorphExpression{
                 expr_type: concrete,
                 field_or_monomorph_idx: infer_expr.field_or_monomorph_idx,
                 type_id: infer_expr.type_id,
             });
+        }
         Ok(())
+    }
     fn progress_expr(&mut self, ctx: &mut Ctx, idx: i32) -> Result<(), ParseError> {
-        let id = self.expr_types[idx as usize].expr_id;
+        let id = self.infer_nodes[idx as usize].expr_id;
         match &ctx.heap[id] {
             Expression::Assignment(expr) => {
                 let id = expr.this;
                 self.progress_assignment_expr(ctx, id)
             },
             Expression::Binding(expr) => {
                 let id = expr.this;
                 self.progress_binding_expr(ctx, id)
             },
             Expression::Conditional(expr) => {
                 let id = expr.this;
                 self.progress_conditional_expr(ctx, id)
             },
             Expression::Binary(expr) => {
                 let id = expr.this;
                 self.progress_binary_expr(ctx, id)
             },
             Expression::Unary(expr) => {
                 let id = expr.this;
                 self.progress_unary_expr(ctx, id)
             },
             Expression::Indexing(expr) => {
                 let id = expr.this;
                 self.progress_indexing_expr(ctx, id)
@@ @@ -1732,52 +1969,51 @@ impl PassTyping { @@
             },
             Expression::Select(expr) => {
                 let id = expr.this;
                 self.progress_select_expr(ctx, id)
             },
             Expression::Literal(expr) => {
                 let id = expr.this;
                 self.progress_literal_expr(ctx, id)
             },
             Expression::Cast(expr) => {
                 let id = expr.this;
                 self.progress_cast_expr(ctx, id)
             },
             Expression::Call(expr) => {
                 let id = expr.this;
                 self.progress_call_expr(ctx, id)
             },
             Expression::Variable(expr) => {
                 let id = expr.this;
                 self.progress_variable_expr(ctx, id)
+            }
+        }
+    }
-    fn progress_assignment_expr(&mut self, ctx: &mut Ctx, id: AssignmentExpressionId) -> Result<(), ParseError> {
+    fn progress_assignment_expr(&mut self, ctx: &mut Ctx, infer_index: InferIndex) -> Result<(), ParseError> {
         use AssignmentOperator as AO;
         let upcast_id = id.upcast();
         let expr = &ctx.heap[id];
         let arg1_expr_id = expr.left;
         let arg2_expr_id = expr.right;
         debug_log!("Assignment expr '{:?}': {}", expr.operation, upcast_id.index);
         debug_log!(" * Before:");
         debug_log!("   - Arg1 type: {}", self.debug_get_display_name(ctx, arg1_expr_id));
         debug_log!("   - Arg2 type: {}", self.debug_get_display_name(ctx, arg2_expr_id));
         debug_log!("   - Expr type: {}", self.debug_get_display_name(ctx, upcast_id));
         // Assignment does not return anything (it operates like a statement)
         let progress_expr = self.apply_forced_constraint(ctx, upcast_id, &VOID_TEMPLATE)?;
         // Apply forced constraint to LHS value
         let progress_forced = match expr.operation {
             AO::Set =>
                 false,
             AO::Concatenated =>
                 self.apply_template_constraint(ctx, arg1_expr_id, &ARRAYLIKE_TEMPLATE)?,
             AO::Multiplied | AO::Divided | AO::Added | AO::Subtracted =>
                 self.apply_template_constraint(ctx, arg1_expr_id, &NUMBERLIKE_TEMPLATE)?,
             AO::Remained | AO::ShiftedLeft | AO::ShiftedRight |
             AO::BitwiseAnded | AO::BitwiseXored | AO::BitwiseOred =>
@@ @@ -1851,88 +2087,80 @@ impl PassTyping { @@
         Ok(())
+    }
     fn progress_binary_expr(&mut self, ctx: &mut Ctx, id: BinaryExpressionId) -> Result<(), ParseError> {
         // Note: our expression type might be fixed by our parent, but we still
         // need to make sure it matches the type associated with our operation.
         use BinaryOperator as BO;
         let upcast_id = id.upcast();
         let expr = &ctx.heap[id];
         let arg1_id = expr.left;
         let arg2_id = expr.right;
         debug_log!("Binary expr '{:?}': {}", expr.operation, upcast_id.index);
         debug_log!(" * Before:");
         debug_log!("   - Arg1 type: {}", self.debug_get_display_name(ctx, arg1_id));
         debug_log!("   - Arg2 type: {}", self.debug_get_display_name(ctx, arg2_id));
         debug_log!("   - Expr type: {}", self.debug_get_display_name(ctx, upcast_id));
         let (progress_expr, progress_arg1, progress_arg2) = match expr.operation {
             BO::Concatenate => {
                 // Two cases: if one of the arguments or the output type is a
                 // string, then all must be strings. Otherwise the arguments
-                // must be arraylike and the output will be a array.
+                // must be arraylike and the output will be an array.
                 let (expr_is_str, expr_is_not_str) = self.type_is_certainly_or_certainly_not_string(ctx, upcast_id);
                 let (arg1_is_str, arg1_is_not_str) = self.type_is_certainly_or_certainly_not_string(ctx, arg1_id);
                 let (arg2_is_str, arg2_is_not_str) = self.type_is_certainly_or_certainly_not_string(ctx, arg2_id);
                 let someone_is_str = expr_is_str || arg1_is_str || arg2_is_str;
                 let someone_is_not_str = expr_is_not_str || arg1_is_not_str || arg2_is_not_str;
                 // Note: this statement is an expression returning the progression bools
                 if someone_is_str {
                     // One of the arguments is a string, then all must be strings
                     self.apply_equal3_constraint(ctx, upcast_id, arg1_id, arg2_id, 0)?
                 } else {
                     let progress_expr = if someone_is_not_str {
                         // Output must be a normal array
                         self.apply_template_constraint(ctx, upcast_id, &ARRAY_TEMPLATE)?
                     } else {
                         // Output may still be anything
                         self.apply_template_constraint(ctx, upcast_id, &ARRAYLIKE_TEMPLATE)?
                     };
                     let progress_arg1 = self.apply_template_constraint(ctx, arg1_id, &ARRAYLIKE_TEMPLATE)?;
                     let progress_arg2 = self.apply_template_constraint(ctx, arg2_id, &ARRAYLIKE_TEMPLATE)?;
                     // If they're all arraylike, then we want the subtype to match
                     let (subtype_expr, subtype_arg1, subtype_arg2) =
                         self.apply_equal3_constraint(ctx, upcast_id, arg1_id, arg2_id, 1)?;
                     (progress_expr || subtype_expr, progress_arg1 || subtype_arg1, progress_arg2 || subtype_arg2)
+                }
             },
             BO::LogicalAnd => {
                 // Forced boolean on all
                 let progress_expr = self.apply_forced_constraint(ctx, upcast_id, &BOOL_TEMPLATE)?;
                 let progress_arg1 = self.apply_forced_constraint(ctx, upcast_id, &BOOL_TEMPLATE)?;
                 let progress_arg2 = self.apply_forced_constraint(ctx, upcast_id, &BOOL_TEMPLATE)?;
                 (progress_expr, progress_arg1, progress_arg2)
             },
             BO::LogicalOr => {
             BO::LogicalAnd | BO::LogicalOr => {
                 // Forced boolean on all
                 let progress_expr = self.apply_forced_constraint(ctx, upcast_id, &BOOL_TEMPLATE)?;
                 let progress_arg1 = self.apply_forced_constraint(ctx, arg1_id, &BOOL_TEMPLATE)?;
                 let progress_arg2 = self.apply_forced_constraint(ctx, arg2_id, &BOOL_TEMPLATE)?;
                 (progress_expr, progress_arg1, progress_arg2)
             },
             BO::BitwiseOr | BO::BitwiseXor | BO::BitwiseAnd | BO::Remainder | BO::ShiftLeft | BO::ShiftRight => {
                 // All equal of integer type
                 let progress_base = self.apply_template_constraint(ctx, upcast_id, &INTEGERLIKE_TEMPLATE)?;
                 let (progress_expr, progress_arg1, progress_arg2) =
                     self.apply_equal3_constraint(ctx, upcast_id, arg1_id, arg2_id, 0)?;
                 (progress_base || progress_expr, progress_base || progress_arg1, progress_base || progress_arg2)
             },
             BO::Equality | BO::Inequality => {
                 // Equal2 on args, forced boolean output
                 let progress_expr = self.apply_forced_constraint(ctx, upcast_id, &BOOL_TEMPLATE)?;
                 let (progress_arg1, progress_arg2) =
                     self.apply_equal2_constraint(ctx, upcast_id, arg1_id, 0, arg2_id, 0)?;
                 (progress_expr, progress_arg1, progress_arg2)
             },
             BO::LessThan | BO::GreaterThan | BO::LessThanEqual | BO::GreaterThanEqual => {
@@ @@ -2093,49 +2321,49 @@ impl PassTyping { @@
         debug_log!("   - ToIdx   type [{}]: {}", progress_idx_base || progress_to, self.debug_get_display_name(ctx, to_id));
         debug_log!("   - Expr    type [{}]: {}", progress_expr, self.debug_get_display_name(ctx, upcast_id));
         if progress_expr { self.queue_expr_parent(ctx, upcast_id); }
         if progress_subject_base || progress_subject { self.queue_expr(ctx, subject_id); }
         if progress_idx_base || progress_from { self.queue_expr(ctx, from_id); }
         if progress_idx_base || progress_to { self.queue_expr(ctx, to_id); }
         Ok(())
+    }
     fn progress_select_expr(&mut self, ctx: &mut Ctx, id: SelectExpressionId) -> Result<(), ParseError> {
         let upcast_id = id.upcast();
         debug_log!("Select expr: {}", upcast_id.index);
         debug_log!(" * Before:");
         debug_log!("   - Subject type: {}", self.debug_get_display_name(ctx, ctx.heap[id].subject));
         debug_log!("   - Expr    type: {}", self.debug_get_display_name(ctx, upcast_id));
         let subject_id = ctx.heap[id].subject;
         let subject_expr_idx = ctx.heap[subject_id].get_unique_id_in_definition();
         let select_expr = &ctx.heap[id];
         let expr_idx = select_expr.unique_id_in_definition;
-        let infer_expr = &self.expr_types[expr_idx as usize];
+        let infer_expr = &self.infer_nodes[expr_idx as usize];
         let extra_idx = infer_expr.extra_data_idx;
         fn try_get_definition_id_from_inference_type<'a>(types: &'a TypeTable, infer_type: &InferenceType) -> Result<Option<&'a DefinedType>, ()> {
             for part in &infer_type.parts {
                 if part.is_marker() || !part.is_concrete() {
                     continue;
+                }
                 // Part is concrete, check if it is an instance of something
                 if let InferenceTypePart::Instance(definition_id, _num_sub) = part {
                     // Lookup type definition and ensure the specified field
                     // name exists on the struct
                     let definition = types.get_base_definition(definition_id);
                     debug_assert!(definition.is_some());
                     let definition = definition.unwrap();
                     return Ok(Some(definition))
                 } else {
                     // Expected an instance of something
                     return Err(())
+                }
+            }
             // Nothing is concrete yet
@@ @@ -2145,470 +2373,470 @@ impl PassTyping { @@
         fn try_get_tuple_size_from_inference_type(infer_type: &InferenceType) -> Result<Option<u32>, ()> {
             for part in &infer_type.parts {
                 if part.is_marker() || !part.is_concrete() {
                     continue;
+                }
                 if let InferenceTypePart::Tuple(size) = part {
                     return Ok(Some(*size));
                 } else {
                     // Expected a tuple
                     return Err(());
+                }
+            }
             // Type is not "defined enough" yet
             Ok(None)
+        }
         let (progress_subject, progress_expr) = match &select_expr.kind {
             SelectKind::StructField(field_name) => {
                 // Handle select of a struct's field
                 if infer_expr.field_or_monomorph_idx < 0 {
                     // We don't know the field or the definition it is pointing to yet
                     // Not yet known, check if we can determine it
-                    let subject_type = &self.expr_types[subject_expr_idx as usize].expr_type;
+                    let subject_type = &self.infer_nodes[subject_expr_idx as usize].expr_type;
                     let type_def = try_get_definition_id_from_inference_type(&ctx.types, subject_type);
                     match type_def {
                         Ok(Some(type_def)) => {
                             // Subject type is known, check if it is a
                             // struct and the field exists on the struct
                             let struct_def = if let DefinedTypeVariant::Struct(struct_def) = &type_def.definition {
                                 struct_def
                             } else {
                                 return Err(ParseError::new_error_at_span(
                                     &ctx.module().source, field_name.span, format!(
                                         "Can only apply field access to structs, got a subject of type '{}'",
                                         subject_type.display_name(&ctx.heap)
+                                    )
                                 ));
                             };
                             let mut struct_def_id = None;
                             for (field_def_idx, field_def) in struct_def.fields.iter().enumerate() {
                                 if field_def.identifier == *field_name {
                                     // Set field definition and index
-                                    let infer_expr = &mut self.expr_types[expr_idx as usize];
+                                    let infer_expr = &mut self.infer_nodes[expr_idx as usize];
                                     infer_expr.field_or_monomorph_idx = field_def_idx as i32;
                                     struct_def_id = Some(type_def.ast_definition);
                                     break;
+                                }
+                            }
                             if struct_def_id.is_none() {
                                 let ast_struct_def = ctx.heap[type_def.ast_definition].as_struct();
                                 return Err(ParseError::new_error_at_span(
                                     &ctx.module().source, field_name.span, format!(
                                         "this field does not exist on the struct '{}'",
                                         ast_struct_def.identifier.value.as_str()
+                                    )
                                 ))
+                            }
                             // Encountered definition and field index for the
                             // first time
                             self.insert_initial_select_polymorph_data(ctx, id, struct_def_id.unwrap());
                         },
                         Ok(None) => {
                             // Type of subject is not yet known, so we
                             // cannot make any progress yet
                             return Ok(())
                         },
                         Err(()) => {
                             return Err(ParseError::new_error_at_span(
                                 &ctx.module().source, field_name.span, format!(
                                     "Can only apply field access to structs, got a subject of type '{}'",
                                     subject_type.display_name(&ctx.heap)
+                                )
                             ));
+                        }
+                    }
+                }
                 // If here then field index is known, and the referenced struct type
                 // information is inserted into `extra_data`. Check to see if we can
                 // do some mutual inference.
                 let poly_data = &mut self.extra_data[extra_idx as usize];
                 let mut poly_progress = HashSet::new(); // TODO: @Performance
                 // Apply to struct's type
                 let signature_type: *mut _ = &mut poly_data.embedded[0];
-                let subject_type: *mut _ = &mut self.expr_types[subject_expr_idx as usize].expr_type;
+                let subject_type: *mut _ = &mut self.infer_nodes[subject_expr_idx as usize].expr_type;
                 let (_, progress_subject) = Self::apply_equal2_signature_constraint(
                     ctx, upcast_id, Some(subject_id), poly_data, &mut poly_progress,
                     signature_type, 0, subject_type, 0
                 )?;
                 if progress_subject {
                     self.expr_queued.push_back(subject_expr_idx);
+                }
                 // Apply to field's type
                 let signature_type: *mut _ = &mut poly_data.returned;
-                let expr_type: *mut _ = &mut self.expr_types[expr_idx as usize].expr_type;
+                let expr_type: *mut _ = &mut self.infer_nodes[expr_idx as usize].expr_type;
                 let (_, progress_expr) = Self::apply_equal2_signature_constraint(
                     ctx, upcast_id, None, poly_data, &mut poly_progress,
                     signature_type, 0, expr_type, 0
                 )?;
                 if progress_expr {
                     if let Some(parent_id) = ctx.heap[upcast_id].parent_expr_id() {
                         let parent_idx = ctx.heap[parent_id].get_unique_id_in_definition();
                         self.expr_queued.push_back(parent_idx);
+                    }
+                }
                 // Reapply progress in polymorphic variables to struct's type
                 let signature_type: *mut _ = &mut poly_data.embedded[0];
-                let subject_type: *mut _ = &mut self.expr_types[subject_expr_idx as usize].expr_type;
+                let subject_type: *mut _ = &mut self.infer_nodes[subject_expr_idx as usize].expr_type;
                 let progress_subject = Self::apply_equal2_polyvar_constraint(
                     poly_data, &poly_progress, signature_type, subject_type
                 );
                 let signature_type: *mut _ = &mut poly_data.returned;
-                let expr_type: *mut _ = &mut self.expr_types[expr_idx as usize].expr_type;
+                let expr_type: *mut _ = &mut self.infer_nodes[expr_idx as usize].expr_type;
                 let progress_expr = Self::apply_equal2_polyvar_constraint(
                     poly_data, &poly_progress, signature_type, expr_type
                 );
                 (progress_subject, progress_expr)
             },
             SelectKind::TupleMember(member_index) => {
                 let member_index = *member_index;
                 if infer_expr.field_or_monomorph_idx < 0 {
                     // We don't know what kind of tuple we're accessing yet
-                    let subject_type = &self.expr_types[subject_expr_idx as usize].expr_type;
+                    let subject_type = &self.infer_nodes[subject_expr_idx as usize].expr_type;
                     let tuple_size = try_get_tuple_size_from_inference_type(subject_type);
                     match tuple_size {
                         Ok(Some(enum_size)) => {
                             // Make sure we don't access an element outside of
                             // the tuple's bounds
                             if member_index >= enum_size as u64 {
                                 return Err(ParseError::new_error_at_span(
                                     &ctx.module().source, select_expr.full_span, format!(
                                         "element index {} is out of bounds, tuple has {} elements",
                                         member_index, enum_size
+                                    )
                                 ));
+                            }
                             // Within bounds, so set the index (such that we
                             // will not perform this lookup again)
-                            let infer_expr = &mut self.expr_types[expr_idx as usize];
+                            let infer_expr = &mut self.infer_nodes[expr_idx as usize];
                             infer_expr.field_or_monomorph_idx = member_index as i32;
                         },
                         Ok(None) => {
                             // Nothing is known about the tuple yet
                             return Ok(());
                         },
                         Err(()) => {
                             return Err(ParseError::new_error_at_span(
                                 &ctx.module().source, select_expr.full_span, format!(
                                     "Can only apply tuple element selection to tuples, got a subject of type '{}'",
                                     subject_type.display_name(&ctx.heap)
+                                )
                             ));
+                        }
+                    }
+                }
                 // If here then we know which member we're accessing. So seek
                 // that member in the subject type and apply inference.
-                let subject_type = &self.expr_types[subject_expr_idx as usize].expr_type;
+                let subject_type = &self.infer_nodes[subject_expr_idx as usize].expr_type;
                 let mut member_start_idx = 1;
                 for _ in 0..member_index {
                     member_start_idx = InferenceType::find_subtree_end_idx(&subject_type.parts, member_start_idx);
+                }
                 let (progress_expr, progress_subject) = self.apply_equal2_constraint(
                     ctx, upcast_id, upcast_id, 0, subject_id, member_start_idx
                 )?;
                 (progress_subject, progress_expr)
             },
         };
         if progress_subject { self.queue_expr(ctx, subject_id); }
         if progress_expr { self.queue_expr_parent(ctx, upcast_id); }
         debug_log!(" * After:");
         debug_log!("   - Subject type [{}]: {}", progress_subject, self.debug_get_display_name(ctx, subject_id));
         debug_log!("   - Expr    type [{}]: {}", progress_expr, self.debug_get_display_name(ctx, upcast_id));
         Ok(())
+    }
     fn progress_literal_expr(&mut self, ctx: &mut Ctx, id: LiteralExpressionId) -> Result<(), ParseError> {
         let upcast_id = id.upcast();
         let expr = &ctx.heap[id];
         let expr_idx = expr.unique_id_in_definition;
-        let extra_idx = self.expr_types[expr_idx as usize].extra_data_idx;
+        let extra_idx = self.infer_nodes[expr_idx as usize].extra_data_idx;
         debug_log!("Literal expr: {}", upcast_id.index);
         debug_log!(" * Before:");
         debug_log!("   - Expr type: {}", self.debug_get_display_name(ctx, upcast_id));
         let progress_expr = match &expr.value {
             Literal::Null => {
                 self.apply_template_constraint(ctx, upcast_id, &MESSAGE_TEMPLATE)?
             },
             Literal::Integer(_) => {
                 self.apply_template_constraint(ctx, upcast_id, &INTEGERLIKE_TEMPLATE)?
             },
             Literal::True | Literal::False => {
                 self.apply_forced_constraint(ctx, upcast_id, &BOOL_TEMPLATE)?
             },
             Literal::Character(_) => {
                 self.apply_forced_constraint(ctx, upcast_id, &CHARACTER_TEMPLATE)?
             },
             Literal::String(_) => {
                 self.apply_forced_constraint(ctx, upcast_id, &STRING_TEMPLATE)?
             },
             Literal::Struct(data) => {
                 let extra = &mut self.extra_data[extra_idx as usize];
                 for _poly in &extra.poly_vars {
                     debug_log!(" * Poly: {}", _poly.display_name(&ctx.heap));
+                }
                 let mut poly_progress = HashSet::new();
                 debug_assert_eq!(extra.embedded.len(), data.fields.len());
                 debug_log!(" * During (inferring types from fields and struct type):");
                 // Mutually infer field signature/expression types
                 for (field_idx, field) in data.fields.iter().enumerate() {
                     let field_expr_id = field.value;
                     let field_expr_idx = ctx.heap[field_expr_id].get_unique_id_in_definition();
                     let signature_type: *mut _ = &mut extra.embedded[field_idx];
-                    let field_type: *mut _ = &mut self.expr_types[field_expr_idx as usize].expr_type;
+                    let field_type: *mut _ = &mut self.infer_nodes[field_expr_idx as usize].expr_type;
                     let (_, progress_arg) = Self::apply_equal2_signature_constraint(
                         ctx, upcast_id, Some(field_expr_id), extra, &mut poly_progress,
                         signature_type, 0, field_type, 0
                     )?;
                     debug_log!(
                         "   - Field {} type | sig: {}, field: {}", field_idx,
                         unsafe{&*signature_type}.display_name(&ctx.heap),
                         unsafe{&*field_type}.display_name(&ctx.heap)
                     );
                     if progress_arg {
                         self.expr_queued.push_back(field_expr_idx);
+                    }
+                }
                 debug_log!("   - Field poly progress | {:?}", poly_progress);
                 // Same for the type of the struct itself
                 let signature_type: *mut _ = &mut extra.returned;
-                let expr_type: *mut _ = &mut self.expr_types[expr_idx as usize].expr_type;
+                let expr_type: *mut _ = &mut self.infer_nodes[expr_idx as usize].expr_type;
                 let (_, progress_expr) = Self::apply_equal2_signature_constraint(
                     ctx, upcast_id, None, extra, &mut poly_progress,
                     signature_type, 0, expr_type, 0
                 )?;
                 debug_log!(
                     "   - Ret type | sig: {}, expr: {}",
                     unsafe{&*signature_type}.display_name(&ctx.heap),
                     unsafe{&*expr_type}.display_name(&ctx.heap)
                 );
                 debug_log!("   - Ret poly progress | {:?}", poly_progress);
                 if progress_expr {
                     // TODO: @cleanup, cannot call utility self.queue_parent thingo
                     if let Some(parent_id) = ctx.heap[upcast_id].parent_expr_id() {
                         let parent_idx = ctx.heap[parent_id].get_unique_id_in_definition();
                         self.expr_queued.push_back(parent_idx);
+                    }
+                }
                 // Check which expressions use the polymorphic arguments. If the
                 // polymorphic variables have been progressed then we try to
                 // progress them inside the expression as well.
                 debug_log!(" * During (reinferring from progressed polyvars):");
                 // For all field expressions
                 for field_idx in 0..extra.embedded.len() {
                     // Note: fields in extra.embedded are in the same order as
                     // they are specified in the literal. Whereas
                     // `data.fields[...].field_idx` points to the field in the
                     // struct definition.
                     let signature_type: *mut _ = &mut extra.embedded[field_idx];
                     let field_expr_id = data.fields[field_idx].value;
                     let field_expr_idx = ctx.heap[field_expr_id].get_unique_id_in_definition();
-                    let field_type: *mut _ = &mut self.expr_types[field_expr_idx as usize].expr_type;
+                    let field_type: *mut _ = &mut self.infer_nodes[field_expr_idx as usize].expr_type;
                     let progress_arg = Self::apply_equal2_polyvar_constraint(
                         extra, &poly_progress, signature_type, field_type
                     );
                     debug_log!(
                         "   - Field {} type | sig: {}, field: {}", field_idx,
                         unsafe{&*signature_type}.display_name(&ctx.heap),
                         unsafe{&*field_type}.display_name(&ctx.heap)
                     );
                     if progress_arg {
                         self.expr_queued.push_back(field_expr_idx);
+                    }
+                }
                 // For the return type
                 let signature_type: *mut _ = &mut extra.returned;
-                let expr_type: *mut _ = &mut self.expr_types[expr_idx as usize].expr_type;
+                let expr_type: *mut _ = &mut self.infer_nodes[expr_idx as usize].expr_type;
                 let progress_expr = Self::apply_equal2_polyvar_constraint(
                     extra, &poly_progress, signature_type, expr_type
                 );
                 progress_expr
             },
             Literal::Enum(_) => {
                 let extra = &mut self.extra_data[extra_idx as usize];
                 for _poly in &extra.poly_vars {
                     debug_log!(" * Poly: {}", _poly.display_name(&ctx.heap));
+                }
                 let mut poly_progress = HashSet::new();
                 debug_log!(" * During (inferring types from return type)");
                 let signature_type: *mut _ = &mut extra.returned;
-                let expr_type: *mut _ = &mut self.expr_types[expr_idx as usize].expr_type;
+                let expr_type: *mut _ = &mut self.infer_nodes[expr_idx as usize].expr_type;
                 let (_, progress_expr) = Self::apply_equal2_signature_constraint(
                     ctx, upcast_id, None, extra, &mut poly_progress,
                     signature_type, 0, expr_type, 0
                 )?;
                 debug_log!(
                     "   - Ret type | sig: {}, expr: {}",
                     unsafe{&*signature_type}.display_name(&ctx.heap),
                     unsafe{&*expr_type}.display_name(&ctx.heap)
                 );
                 if progress_expr {
                     // TODO: @cleanup
                     if let Some(parent_id) = ctx.heap[upcast_id].parent_expr_id() {
                         let parent_idx = ctx.heap[parent_id].get_unique_id_in_definition();
                         self.expr_queued.push_back(parent_idx);
+                    }
+                }
                 debug_log!(" * During (reinferring from progress polyvars):");
                 let progress_expr = Self::apply_equal2_polyvar_constraint(
                     extra, &poly_progress, signature_type, expr_type
                 );
                 progress_expr
             },
             Literal::Union(data) => {
                 let extra = &mut self.extra_data[extra_idx as usize];
                 for _poly in &extra.poly_vars {
                     debug_log!(" * Poly: {}", _poly.display_name(&ctx.heap));
+                }
                 let mut poly_progress = HashSet::new();
                 debug_assert_eq!(extra.embedded.len(), data.values.len());
                 debug_log!(" * During (inferring types from variant values and union type):");
                 // Mutually infer union variant values
                 for (value_idx, value_expr_id) in data.values.iter().enumerate() {
                     let value_expr_id = *value_expr_id;
                     let value_expr_idx = ctx.heap[value_expr_id].get_unique_id_in_definition();
                     let signature_type: *mut _ = &mut extra.embedded[value_idx];
-                    let value_type: *mut _ = &mut self.expr_types[value_expr_idx as usize].expr_type;
+                    let value_type: *mut _ = &mut self.infer_nodes[value_expr_idx as usize].expr_type;
                     let (_, progress_arg) = Self::apply_equal2_signature_constraint(
                         ctx, upcast_id, Some(value_expr_id), extra, &mut poly_progress,
                         signature_type, 0, value_type, 0
                     )?;
                     debug_log!(
                         "   - Value {} type | sig: {}, field: {}", value_idx,
                         unsafe{&*signature_type}.display_name(&ctx.heap),
                         unsafe{&*value_type}.display_name(&ctx.heap)
                     );
                     if progress_arg {
                         self.expr_queued.push_back(value_expr_idx);
+                    }
+                }
                 debug_log!("   - Field poly progress | {:?}", poly_progress);
                 // Infer type of union itself
                 let signature_type: *mut _ = &mut extra.returned;
-                let expr_type: *mut _ = &mut self.expr_types[expr_idx as usize].expr_type;
+                let expr_type: *mut _ = &mut self.infer_nodes[expr_idx as usize].expr_type;
                 let (_, progress_expr) = Self::apply_equal2_signature_constraint(
                     ctx, upcast_id, None, extra, &mut poly_progress,
                     signature_type, 0, expr_type, 0
                 )?;
                 debug_log!(
                     "   - Ret type | sig: {}, expr: {}",
                     unsafe{&*signature_type}.display_name(&ctx.heap),
                     unsafe{&*expr_type}.display_name(&ctx.heap)
                 );
                 debug_log!("   - Ret poly progress | {:?}", poly_progress);
                 if progress_expr {
                     // TODO: @cleanup, borrowing rules
                     if let Some(parent_id) = ctx.heap[upcast_id].parent_expr_id() {
                         let parent_idx = ctx.heap[parent_id].get_unique_id_in_definition();
                         self.expr_queued.push_back(parent_idx);
+                    }
+                }
                 debug_log!(" * During (reinferring from progress polyvars):");
                 // For all embedded values of the union variant
                 for value_idx in 0..extra.embedded.len() {
                     let signature_type: *mut _ = &mut extra.embedded[value_idx];
                     let value_expr_id = data.values[value_idx];
                     let value_expr_idx = ctx.heap[value_expr_id].get_unique_id_in_definition();
-                    let value_type: *mut _ = &mut self.expr_types[value_expr_idx as usize].expr_type;
+                    let value_type: *mut _ = &mut self.infer_nodes[value_expr_idx as usize].expr_type;
                     let progress_arg = Self::apply_equal2_polyvar_constraint(
                         extra, &poly_progress, signature_type, value_type
                     );
                     debug_log!(
                         "   - Value {} type | sig: {}, value: {}", value_idx,
                         unsafe{&*signature_type}.display_name(&ctx.heap),
                         unsafe{&*value_type}.display_name(&ctx.heap)
                     );
                     if progress_arg {
                         self.expr_queued.push_back(value_expr_idx);
+                    }
+                }
                 // And for the union type itself
                 let signature_type: *mut _ = &mut extra.returned;
-                let expr_type: *mut _ = &mut self.expr_types[expr_idx as usize].expr_type;
+                let expr_type: *mut _ = &mut self.infer_nodes[expr_idx as usize].expr_type;
                 let progress_expr = Self::apply_equal2_polyvar_constraint(
                     extra, &poly_progress, signature_type, expr_type
                 );
                 progress_expr
             },
             Literal::Array(data) => {
                 let expr_elements = self.expr_buffer.start_section_initialized(data.as_slice());
                 debug_log!("Array expr ({} elements): {}", expr_elements.len(), upcast_id.index);
                 debug_log!(" * Before:");
                 debug_log!("   - Expr type: {}", self.debug_get_display_name(ctx, upcast_id));
                 // All elements should have an equal type
                 let mut bool_buffer = self.bool_buffer.start_section();
                 self.apply_equal_n_constraint(ctx, upcast_id, &expr_elements, &mut bool_buffer)?;
                 for (progress_arg, arg_id) in bool_buffer.iter_copied().zip(expr_elements.iter_copied()) {
                     if progress_arg {
                         self.queue_expr(ctx, arg_id);
+                    }
+                }
                 // And the output should be an array of the element types
                 let mut progress_expr = self.apply_template_constraint(ctx, upcast_id, &ARRAY_TEMPLATE)?;
@@ @@ -2635,49 +2863,49 @@ impl PassTyping { @@
             Literal::Tuple(data) => {
                 let expr_elements = self.expr_buffer.start_section_initialized(data.as_slice());
                 debug_log!("Tuple expr ({} elements): {}", expr_elements.len(), upcast_id.index);
                 debug_log!(" * Before:");
                 debug_log!("   - Expr type: {}", self.debug_get_display_name(ctx, upcast_id));
                 // Initial tuple constraint
                 let num_members = expr_elements.len();
                 let mut initial_type = Vec::with_capacity(num_members + 1); // TODO: @performance
                 initial_type.push(InferenceTypePart::Tuple(num_members as u32));
                 for _ in 0..num_members {
                     initial_type.push(InferenceTypePart::Unknown);
+                }
                 let mut progress_expr = self.apply_template_constraint(ctx, upcast_id, &initial_type)?;
                 // The elements of the tuple can have any type, but they must
                 // end up as arguments to the output tuple type.
                 debug_log!(" * During (checking expressions constituting tuple):");
                 for (member_expr_index, member_expr_id) in expr_elements.iter_copied().enumerate() {
                     // For the current expression index, (re)compute the
                     // position in the tuple type where the types should match.
                     let mut start_index = 1; // first element is Tuple type, second is the first child
                     for _ in 0..member_expr_index {
                         let tuple_expr_index = ctx.heap[id].unique_id_in_definition;
-                        let tuple_type = &self.expr_types[tuple_expr_index as usize].expr_type;
+                        let tuple_type = &self.infer_nodes[tuple_expr_index as usize].expr_type;
                         start_index = InferenceType::find_subtree_end_idx(&tuple_type.parts, start_index);
                         debug_assert_ne!(start_index, tuple_type.parts.len()); // would imply less tuple type children than member expressions
+                    }
                     // Apply the constraint
                     let (member_progress_expr, member_progress) = self.apply_equal2_constraint(
                         ctx, upcast_id, upcast_id, start_index, member_expr_id, 0
                     )?;
                     debug_log!("   - Member {} type | {}", member_expr_index, self.debug_get_display_name(ctx, *member_expr_id));
                     progress_expr = progress_expr || member_progress_expr;
                     if member_progress {
                         self.queue_expr(ctx, member_expr_id);
+                    }
+                }
                 expr_elements.forget();
                 progress_expr
+            }
         };
         debug_log!(" * After:");
         debug_log!("   - Expr type [{}]: {}", progress_expr, self.debug_get_display_name(ctx, upcast_id));
@@ @@ -2695,50 +2923,50 @@ impl PassTyping { @@
         debug_log!(" * Before:");
         debug_log!("   - Expr type:    {}", self.debug_get_display_name(ctx, upcast_id));
         debug_log!("   - Subject type: {}", self.debug_get_display_name(ctx, expr.subject));
         // The cast expression might have its output type fixed by the
         // programmer, so apply that type to the output. Apart from that casting
         // acts like a blocker for two-way inference. So we'll just have to wait
         // until we know if the cast is valid.
         // TODO: Another thing that has to be updated the moment the type
         //  inferencer is fully index/job-based
         let infer_type = self.determine_inference_type_from_parser_type_elements(&expr.to_type.elements, true);
         let expr_progress = self.apply_template_constraint(ctx, upcast_id, &infer_type.parts)?;
         if expr_progress {
             self.queue_expr_parent(ctx, upcast_id);
+        }
         // Check if the two types are compatible
         debug_log!(" * After:");
         debug_log!("   - Expr type [{}]: {}", expr_progress, self.debug_get_display_name(ctx, upcast_id));
         debug_log!("   - Note that the subject type can never be inferred");
         debug_log!(" * Decision:");
         let subject_idx = ctx.heap[expr.subject].get_unique_id_in_definition();
         let expr_type = &self.expr_types[expr_idx as usize].expr_type;
         let subject_type = &self.expr_types[subject_idx as usize].expr_type;
         let expr_type = &self.infer_nodes[expr_idx as usize].expr_type;
         let subject_type = &self.infer_nodes[subject_idx as usize].expr_type;
         if !expr_type.is_done || !subject_type.is_done {
             // Not yet done
             debug_log!("   - Casting is valid: unknown as the types are not yet complete");
             return Ok(())
+        }
         // Valid casts: (bool, integer, character) can always be cast to one
         // another. A cast from a type to itself is also valid.
         fn is_bool_int_or_char(parts: &[InferenceTypePart]) -> bool {
             return parts.len() == 1 && (
                 parts[0] == InferenceTypePart::Bool ||
                 parts[0] == InferenceTypePart::Character ||
                 parts[0].is_concrete_integer()
             );
+        }
         let is_valid = if is_bool_int_or_char(&expr_type.parts) && is_bool_int_or_char(&subject_type.parts) {
             true
         } else if expr_type.parts == subject_type.parts {
             true
         } else {
             false
         };
@@ @@ -2747,171 +2975,171 @@ impl PassTyping { @@
         if !is_valid {
             let cast_expr = &ctx.heap[id];
             let subject_expr = &ctx.heap[cast_expr.subject];
             return Err(ParseError::new_error_str_at_span(
                 &ctx.module().source, cast_expr.full_span, "invalid casting operation"
             ).with_info_at_span(
                 &ctx.module().source, subject_expr.full_span(), format!(
                     "cannot cast the argument type '{}' to the cast type '{}'",
                     subject_type.display_name(&ctx.heap),
                     expr_type.display_name(&ctx.heap)
+                )
             ));
+        }
         Ok(())
+    }
     // TODO: @cleanup, see how this can be cleaned up once I implement
     //  polymorphic struct/enum/union literals. These likely follow the same
     //  pattern as here.
     fn progress_call_expr(&mut self, ctx: &mut Ctx, id: CallExpressionId) -> Result<(), ParseError> {
         let upcast_id = id.upcast();
         let expr = &ctx.heap[id];
         let expr_idx = expr.unique_id_in_definition;
-        let extra_idx = self.expr_types[expr_idx as usize].extra_data_idx;
+        let extra_idx = self.infer_nodes[expr_idx as usize].extra_data_idx;
         debug_log!("Call expr '{}': {}", ctx.heap[expr.definition].identifier().value.as_str(), upcast_id.index);
         debug_log!(" * Before:");
         debug_log!("   - Expr type: {}", self.debug_get_display_name(ctx, upcast_id));
         debug_log!(" * During (inferring types from arguments and return type):");
         let extra = &mut self.extra_data[extra_idx as usize];
         // Check if we can make progress using the arguments and/or return types
         // while keeping track of the polyvars we've extended
         let mut poly_progress = HashSet::new();
         debug_assert_eq!(extra.embedded.len(), expr.arguments.len());
         for (call_arg_idx, arg_id) in expr.arguments.clone().into_iter().enumerate() {
             let arg_expr_idx = ctx.heap[arg_id].get_unique_id_in_definition();
             let signature_type: *mut _ = &mut extra.embedded[call_arg_idx];
-            let argument_type: *mut _ = &mut self.expr_types[arg_expr_idx as usize].expr_type;
+            let argument_type: *mut _ = &mut self.infer_nodes[arg_expr_idx as usize].expr_type;
             let (_, progress_arg) = Self::apply_equal2_signature_constraint(
                 ctx, upcast_id, Some(arg_id), extra, &mut poly_progress,
                 signature_type, 0, argument_type, 0
             )?;
             debug_log!(
                 "   - Arg {} type | sig: {}, arg: {}", call_arg_idx,
                 unsafe{&*signature_type}.display_name(&ctx.heap),
                 unsafe{&*argument_type}.display_name(&ctx.heap));
             if progress_arg {
                 // Progressed argument expression
                 self.expr_queued.push_back(arg_expr_idx);
+            }
+        }
         // Do the same for the return type
         let signature_type: *mut _ = &mut extra.returned;
-        let expr_type: *mut _ = &mut self.expr_types[expr_idx as usize].expr_type;
+        let expr_type: *mut _ = &mut self.infer_nodes[expr_idx as usize].expr_type;
         let (_, progress_expr) = Self::apply_equal2_signature_constraint(
             ctx, upcast_id, None, extra, &mut poly_progress,
             signature_type, 0, expr_type, 0
         )?;
         debug_log!(
             "   - Ret type | sig: {}, expr: {}",
             unsafe{&*signature_type}.display_name(&ctx.heap),
             unsafe{&*expr_type}.display_name(&ctx.heap)
         );
         if progress_expr {
             // TODO: @cleanup, cannot call utility self.queue_parent thingo
             if let Some(parent_id) = ctx.heap[upcast_id].parent_expr_id() {
                 let parent_idx = ctx.heap[parent_id].get_unique_id_in_definition();
                 self.expr_queued.push_back(parent_idx);
+            }
+        }
         // If we did not have an error in the polymorph inference above, then
         // reapplying the polymorph type to each argument type and the return
         // type should always succeed.
         debug_log!(" * During (reinferring from progressed polyvars):");
         for (_poly_idx, _poly_var) in extra.poly_vars.iter().enumerate() {
             debug_log!("   - Poly {} | sig: {}", _poly_idx, _poly_var.display_name(&ctx.heap));
+        }
         // TODO: @performance If the algorithm is changed to be more "on demand
         //  argument re-evaluation", instead of "all-argument re-evaluation",
         //  then this is no longer true
         for arg_idx in 0..extra.embedded.len() {
             let signature_type: *mut _ = &mut extra.embedded[arg_idx];
             let arg_expr_id = expr.arguments[arg_idx];
             let arg_expr_idx = ctx.heap[arg_expr_id].get_unique_id_in_definition();
-            let arg_type: *mut _ = &mut self.expr_types[arg_expr_idx as usize].expr_type;
+            let arg_type: *mut _ = &mut self.infer_nodes[arg_expr_idx as usize].expr_type;
             let progress_arg = Self::apply_equal2_polyvar_constraint(
                 extra, &poly_progress,
                 signature_type, arg_type
             );
             debug_log!(
                 "   - Arg {} type | sig: {}, arg: {}", arg_idx,
                 unsafe{&*signature_type}.display_name(&ctx.heap),
                 unsafe{&*arg_type}.display_name(&ctx.heap)
             );
             if progress_arg {
                 self.expr_queued.push_back(arg_expr_idx);
+            }
+        }
         // Once more for the return type
         let signature_type: *mut _ = &mut extra.returned;
-        let ret_type: *mut _ = &mut self.expr_types[expr_idx as usize].expr_type;
+        let ret_type: *mut _ = &mut self.infer_nodes[expr_idx as usize].expr_type;
         let progress_ret = Self::apply_equal2_polyvar_constraint(
             extra, &poly_progress, signature_type, ret_type
         );
         debug_log!(
             "   - Ret type | sig: {}, arg: {}",
             unsafe{&*signature_type}.display_name(&ctx.heap),
             unsafe{&*ret_type}.display_name(&ctx.heap)
         );
         if progress_ret {
             self.queue_expr_parent(ctx, upcast_id);
+        }
         debug_log!(" * After:");
         debug_log!("   - Expr type: {}", self.debug_get_display_name(ctx, upcast_id));
         Ok(())
+    }
     fn progress_variable_expr(&mut self, ctx: &mut Ctx, id: VariableExpressionId) -> Result<(), ParseError> {
         let upcast_id = id.upcast();
         let var_expr = &ctx.heap[id];
         let var_expr_idx = var_expr.unique_id_in_definition;
         let var_id = var_expr.declaration.unwrap();
         debug_log!("Variable expr '{}': {}", ctx.heap[var_id].identifier.value.as_str(), upcast_id.index);
         debug_log!(" * Before:");
         debug_log!("   - Var  type: {}", self.var_types.get(&var_id).unwrap().var_type.display_name(&ctx.heap));
         debug_log!("   - Expr type: {}", self.debug_get_display_name(ctx, upcast_id));
         // Retrieve shared variable type and expression type and apply inference
         let var_data = self.var_types.get_mut(&var_id).unwrap();
-        let expr_type = &mut self.expr_types[var_expr_idx as usize].expr_type;
+        let expr_type = &mut self.infer_nodes[var_expr_idx as usize].expr_type;
         let infer_res = unsafe{ InferenceType::infer_subtrees_for_both_types(
             &mut var_data.var_type as *mut _, 0, expr_type, 0
         ) };
         if infer_res == DualInferenceResult::Incompatible {
             let var_decl = &ctx.heap[var_id];
             return Err(ParseError::new_error_at_span(
                 &ctx.module().source, var_decl.identifier.span, format!(
                     "Conflicting types for this variable, previously assigned the type '{}'",
                     var_data.var_type.display_name(&ctx.heap)
+                )
             ).with_info_at_span(
                 &ctx.module().source, var_expr.identifier.span, format!(
                     "But inferred to have incompatible type '{}' here",
                     expr_type.display_name(&ctx.heap)
+                )
             ))
+        }
         let progress_var = infer_res.modified_lhs();
         let progress_expr = infer_res.modified_rhs();
         if progress_var {
             // Let other variable expressions using this type progress as well
@@ @@ -2972,122 +3200,122 @@ impl PassTyping { @@
         debug_log!(" * After:");
         debug_log!("   - Var  type [{}]: {}", progress_var, self.var_types.get(&var_id).unwrap().var_type.display_name(&ctx.heap));
         debug_log!("   - Expr type [{}]: {}", progress_expr, self.debug_get_display_name(ctx, upcast_id));
         Ok(())
+    }
     fn queue_expr_parent(&mut self, ctx: &Ctx, expr_id: ExpressionId) {
         if let ExpressionParent::Expression(parent_expr_id, _) = &ctx.heap[expr_id].parent() {
             let expr_idx = ctx.heap[*parent_expr_id].get_unique_id_in_definition();
             self.expr_queued.push_back(expr_idx);
+        }
+    }
     fn queue_expr(&mut self, ctx: &Ctx, expr_id: ExpressionId) {
         let expr_idx = ctx.heap[expr_id].get_unique_id_in_definition();
         self.expr_queued.push_back(expr_idx);
+    }
     // first returned is certainly string, second is certainly not
     fn type_is_certainly_or_certainly_not_string(&self, ctx: &Ctx, expr_id: ExpressionId) -> (bool, bool) {
         let expr_idx = ctx.heap[expr_id].get_unique_id_in_definition();
-        let expr_type = &self.expr_types[expr_idx as usize].expr_type;
+        let expr_type = &self.infer_nodes[expr_idx as usize].expr_type;
         if expr_type.is_done {
             if expr_type.parts[0] == InferenceTypePart::String {
                 return (true, false);
             } else {
                 return (false, true);
+            }
+        }
         (false, false)
+    }
     /// Applies a template type constraint: the type associated with the
     /// supplied expression will be molded into the provided `template`. But
     /// will be considered valid if the template could've been molded into the
     /// expression type as well. Hence the template may be fully specified (e.g.
     /// a bool) or contain "inference" variables (e.g. an array of T)
     fn apply_template_constraint(
         &mut self, ctx: &Ctx, expr_id: ExpressionId, template: &[InferenceTypePart]
     ) -> Result<bool, ParseError> {
         let expr_idx = ctx.heap[expr_id].get_unique_id_in_definition(); // TODO: @Temp
-        let expr_type = &mut self.expr_types[expr_idx as usize].expr_type;
+        let expr_type = &mut self.infer_nodes[expr_idx as usize].expr_type;
         match InferenceType::infer_subtree_for_single_type(expr_type, 0, template, 0, false) {
             SingleInferenceResult::Modified => Ok(true),
             SingleInferenceResult::Unmodified => Ok(false),
             SingleInferenceResult::Incompatible => Err(
                 self.construct_template_type_error(ctx, expr_id, template)
+            )
+        }
+    }
     fn apply_template_constraint_to_types(
         to_infer: *mut InferenceType, to_infer_start_idx: usize,
         template: &[InferenceTypePart], template_start_idx: usize
     ) -> Result<bool, ()> {
         match InferenceType::infer_subtree_for_single_type(
             unsafe{ &mut *to_infer }, to_infer_start_idx,
             template, template_start_idx, false
         ) {
             SingleInferenceResult::Modified => Ok(true),
             SingleInferenceResult::Unmodified => Ok(false),
             SingleInferenceResult::Incompatible => Err(()),
+        }
+    }
     /// Applies a forced constraint: the supplied expression's type MUST be
     /// inferred from the template, the other way around is considered invalid.
     fn apply_forced_constraint(
         &mut self, ctx: &Ctx, expr_id: ExpressionId, template: &[InferenceTypePart]
     ) -> Result<bool, ParseError> {
         let expr_idx = ctx.heap[expr_id].get_unique_id_in_definition();
-        let expr_type = &mut self.expr_types[expr_idx as usize].expr_type;
+        let expr_type = &mut self.infer_nodes[expr_idx as usize].expr_type;
         match InferenceType::infer_subtree_for_single_type(expr_type, 0, template, 0, true) {
             SingleInferenceResult::Modified => Ok(true),
             SingleInferenceResult::Unmodified => Ok(false),
             SingleInferenceResult::Incompatible => Err(
                 self.construct_template_type_error(ctx, expr_id, template)
+            )
+        }
+    }
     /// Applies a type constraint that expects the two provided types to be
     /// equal. We attempt to make progress in inferring the types. If the call
     /// is successful then the composition of all types are made equal.
     /// The "parent" `expr_id` is provided to construct errors.
     fn apply_equal2_constraint(
         &mut self, ctx: &Ctx, expr_id: ExpressionId,
         arg1_id: ExpressionId, arg1_start_idx: usize,
         arg2_id: ExpressionId, arg2_start_idx: usize
     ) -> Result<(bool, bool), ParseError> {
         let arg1_expr_idx = ctx.heap[arg1_id].get_unique_id_in_definition(); // TODO: @Temp
         let arg2_expr_idx = ctx.heap[arg2_id].get_unique_id_in_definition();
         let arg1_type: *mut _ = &mut self.expr_types[arg1_expr_idx as usize].expr_type;
         let arg2_type: *mut _ = &mut self.expr_types[arg2_expr_idx as usize].expr_type;
         let arg1_type: *mut _ = &mut self.infer_nodes[arg1_expr_idx as usize].expr_type;
         let arg2_type: *mut _ = &mut self.infer_nodes[arg2_expr_idx as usize].expr_type;
         let infer_res = unsafe{ InferenceType::infer_subtrees_for_both_types(
             arg1_type, arg1_start_idx,
             arg2_type, arg2_start_idx
         ) };
         if infer_res == DualInferenceResult::Incompatible {
             return Err(self.construct_arg_type_error(ctx, expr_id, arg1_id, arg2_id));
+        }
         Ok((infer_res.modified_lhs(), infer_res.modified_rhs()))
+    }
     /// Applies an equal2 constraint between a signature type (e.g. a function
     /// argument or struct field) and an expression whose type should match that
     /// expression. If we make progress on the signature, then we try to see if
     /// any of the embedded polymorphic types can be progressed.
     ///
     /// `outer_expr_id` is the main expression we're progressing (e.g. a
     /// function call), while `expr_id` is the embedded expression we're
     /// matching against the signature. `expression_type` and
     /// `expression_start_idx` belong to `expr_id`.
     fn apply_equal2_signature_constraint(
         ctx: &Ctx, outer_expr_id: ExpressionId, expr_id: Option<ExpressionId>,
         polymorph_data: &mut ExtraData, polymorph_progress: &mut HashSet<u32>,
@@ @@ -3201,51 +3429,51 @@ impl PassTyping { @@
                 SingleInferenceResult::Unmodified => false,
                 SingleInferenceResult::Incompatible =>
                     unreachable!("encountered failure while reapplying modified signature to expression after polyvar inference")
+            }
         } else {
             false
+        }
+    }
     /// Applies a type constraint that expects all three provided types to be
     /// equal. In case we can make progress in inferring the types then we
     /// attempt to do so. If the call is successful then the composition of all
     /// types is made equal.
     fn apply_equal3_constraint(
         &mut self, ctx: &Ctx, expr_id: ExpressionId,
         arg1_id: ExpressionId, arg2_id: ExpressionId,
         start_idx: usize
     ) -> Result<(bool, bool, bool), ParseError> {
         // Safety: all points are unique
         //         containers may not be modified
         let expr_expr_idx = ctx.heap[expr_id].get_unique_id_in_definition(); // TODO: @Temp
         let arg1_expr_idx = ctx.heap[arg1_id].get_unique_id_in_definition();
         let arg2_expr_idx = ctx.heap[arg2_id].get_unique_id_in_definition();
         let expr_type: *mut _ = &mut self.expr_types[expr_expr_idx as usize].expr_type;
         let arg1_type: *mut _ = &mut self.expr_types[arg1_expr_idx as usize].expr_type;
         let arg2_type: *mut _ = &mut self.expr_types[arg2_expr_idx as usize].expr_type;
         let expr_type: *mut _ = &mut self.infer_nodes[expr_expr_idx as usize].expr_type;
         let arg1_type: *mut _ = &mut self.infer_nodes[arg1_expr_idx as usize].expr_type;
         let arg2_type: *mut _ = &mut self.infer_nodes[arg2_expr_idx as usize].expr_type;
         let expr_res = unsafe{
             InferenceType::infer_subtrees_for_both_types(expr_type, start_idx, arg1_type, start_idx)
         };
         if expr_res == DualInferenceResult::Incompatible {
             return Err(self.construct_expr_type_error(ctx, expr_id, arg1_id));
+        }
         let args_res = unsafe{
             InferenceType::infer_subtrees_for_both_types(arg1_type, start_idx, arg2_type, start_idx) };
         if args_res == DualInferenceResult::Incompatible {
             return Err(self.construct_arg_type_error(ctx, expr_id, arg1_id, arg2_id));
+        }
         // If all types are compatible, but the second call caused the arg1_type
         // to be expanded, then we must also assign this to expr_type.
         let mut progress_expr = expr_res.modified_lhs();
         let mut progress_arg1 = expr_res.modified_rhs();
         let progress_arg2 = args_res.modified_rhs();
         if args_res.modified_lhs() {
             unsafe {
                 let end_idx = InferenceType::find_subtree_end_idx(&(*arg2_type).parts, start_idx);
                 let subtree = &((*arg2_type).parts[start_idx..end_idx]);
@@ @@ -3274,454 +3502,429 @@ impl PassTyping { @@
                 return Ok(())
             },
 => {
                 // only one type, so nothing to infer
                 progress.push(false);
                 return Ok(())
             },
             n => {
                 for _ in 0..n {
                     progress.push(false);
+                }
+            }
+        }
         // Do pairwise inference, keep track of the last entry we made progress
         // on. Once done we need to update everything to the most-inferred type.
         let mut arg_iter = args.iter_copied();
         let mut last_arg_id = arg_iter.next().unwrap();
         let mut last_lhs_progressed = 0;
         let mut lhs_arg_idx = 0;
         while let Some(next_arg_id) = arg_iter.next() {
             let last_expr_idx = ctx.heap[last_arg_id].get_unique_id_in_definition(); // TODO: @Temp
             let next_expr_idx = ctx.heap[next_arg_id].get_unique_id_in_definition();
             let last_type: *mut _ = &mut self.expr_types[last_expr_idx as usize].expr_type;
             let next_type: *mut _ = &mut self.expr_types[next_expr_idx as usize].expr_type;
             let last_type: *mut _ = &mut self.infer_nodes[last_expr_idx as usize].expr_type;
             let next_type: *mut _ = &mut self.infer_nodes[next_expr_idx as usize].expr_type;
             let res = unsafe {
                 InferenceType::infer_subtrees_for_both_types(last_type, 0, next_type, 0)
             };
             if res == DualInferenceResult::Incompatible {
                 return Err(self.construct_arg_type_error(ctx, expr_id, last_arg_id, next_arg_id));
+            }
             if res.modified_lhs() {
                 // We re-inferred something on the left hand side, so everything
                 // up until now should be re-inferred.
                 progress[lhs_arg_idx] = true;
                 last_lhs_progressed = lhs_arg_idx;
+            }
             progress[lhs_arg_idx + 1] = res.modified_rhs();
             last_arg_id = next_arg_id;
             lhs_arg_idx += 1;
+        }
         // Re-infer everything. Note that we do not need to re-infer the type
         // exactly at `last_lhs_progressed`, but only everything up to it.
         let last_arg_expr_idx = ctx.heap[last_arg_id].get_unique_id_in_definition();
-        let last_type: *mut _ = &mut self.expr_types[last_arg_expr_idx as usize].expr_type;
+        let last_type: *mut _ = &mut self.infer_nodes[last_arg_expr_idx as usize].expr_type;
         for arg_idx in 0..last_lhs_progressed {
             let other_arg_expr_idx = ctx.heap[args[arg_idx]].get_unique_id_in_definition();
-            let arg_type: *mut _ = &mut self.expr_types[other_arg_expr_idx as usize].expr_type;
+            let arg_type: *mut _ = &mut self.infer_nodes[other_arg_expr_idx as usize].expr_type;
             unsafe{
                 (*arg_type).replace_subtree(0, &(*last_type).parts);
+            }
             progress[arg_idx] = true;
+        }
         return Ok(());
+    }
     /// Determines the `InferenceType` for the expression based on the
     /// expression parent. Note that if the parent is another expression, we do
     /// not take special action, instead we let parent expressions fix the type
     /// of subexpressions before they have a chance to call this function.
     fn insert_initial_expr_inference_type(
         &mut self, ctx: &mut Ctx, expr_id: ExpressionId
-    ) -> Result<(), ParseError> {
+    ) -> Result<InferIndex, ParseError> {
         use ExpressionParent as EP;
         use InferenceTypePart as ITP;
         // Set the initial inference type based on the expression parent.
         let expr = &ctx.heap[expr_id];
         let inference_type = match expr.parent() {
             EP::None =>
                 // Should have been set by linker
                 unreachable!(),
             EP::Memory(_) | EP::ExpressionStmt(_) =>
                 // Determined during type inference
                 InferenceType::new(false, false, vec![ITP::Unknown]),
             EP::Expression(parent_id, idx_in_parent) => {
                 // If we are the test expression of a conditional expression,
                 // then we must resolve to a boolean
                 let is_conditional = if let Expression::Conditional(_) = &ctx.heap[*parent_id] {
                     true
                 } else {
                     false
                 };
                 if is_conditional && *idx_in_parent == 0 {
                     InferenceType::new(false, true, vec![ITP::Bool])
                 } else {
                     InferenceType::new(false, false, vec![ITP::Unknown])
+                }
             },
             EP::If(_) | EP::While(_) =>
                 // Must be a boolean
                 InferenceType::new(false, true, vec![ITP::Bool]),
             EP::Return(_) =>
                 // Must match the return type of the function
                 if let DefinitionType::Function(func_id) = self.definition_type {
                     let returned = &ctx.heap[func_id].return_type;
                     self.determine_inference_type_from_parser_type_elements(&returned.elements, true)
                 } else {
                     // Cannot happen: definition always set upon body traversal
                     // and "return" calls in components are illegal.
                     unreachable!();
                 },
             EP::New(_) =>
                 // Must be a component call, which we assign a "Void" return
                 // type
                 InferenceType::new(false, true, vec![ITP::Void]),
         };
         let infer_expr = &mut self.expr_types[expr.get_unique_id_in_definition() as usize];
         let needs_extra_data = match expr {
             Expression::Call(_) => true,
             Expression::Literal(expr) => match expr.value {
                 Literal::Enum(_) | Literal::Union(_) | Literal::Struct(_) => true,
                 _ => false,
             },
             Expression::Select(expr) => match expr.kind {
                 SelectKind::StructField(_) => true,
                 SelectKind::TupleMember(_) => false,
             },
             _ => false,
         };
         if infer_expr.expr_id.is_invalid() {
             // Nothing is set yet
             infer_expr.expr_type = inference_type;
             infer_expr.expr_id = expr_id;
             if needs_extra_data {
                 let extra_idx = self.extra_data.len() as i32;
                 self.extra_data.push(ExtraData::default());
                 infer_expr.extra_data_idx = extra_idx;
+            }
         } else {
             // We already have an entry
             debug_assert!(false, "does this ever happen?");
             if let SingleInferenceResult::Incompatible = InferenceType::infer_subtree_for_single_type(
                 &mut infer_expr.expr_type, 0, &inference_type.parts, 0, false
             ) {
                 return Err(self.construct_expr_type_error(ctx, expr_id, expr_id));
+            }
             debug_assert!((infer_expr.extra_data_idx != -1) == needs_extra_data);
+        }
         let infer_index = self.infer_nodes.len() as InferIndex;
         self.infer_nodes.push(InferenceNode {
             expr_type: inference_type,
             expr_id,
             field_or_monomorph_idx: -1,
             extra_data_idx: -1,
             type_id: TypeId::new_invalid(),
         });
-        Ok(())
+        return Ok(infer_index);
+    }
     fn insert_initial_call_polymorph_data(
         &mut self, ctx: &mut Ctx, call_id: CallExpressionId
     ) {
+    ) -> ExtraIndex {
         // Note: the polymorph variables may be partially specified and may
         // contain references to the wrapping definition's (i.e. the proctype
         // we are currently visiting) polymorphic arguments.
         //
         // The arguments of the call may refer to polymorphic variables in the
         // definition of the function we're calling, not of the wrapping
         // definition. We insert markers in these inferred types to be able to
         // map them back and forth to the polymorphic arguments of the function
         // we are calling.
         let call = &ctx.heap[call_id];
         let extra_data_idx = self.expr_types[call.unique_id_in_definition as usize].extra_data_idx; // TODO: @Temp
         debug_assert!(extra_data_idx != -1, "insert initial call polymorph data, no preallocated ExtraData");
         // Handle the polymorphic arguments (if there are any)
         let num_poly_args = call.parser_type.elements[0].variant.num_embedded();
         let mut poly_args = Vec::with_capacity(num_poly_args);
         for embedded_elements in call.parser_type.iter_embedded(0) {
             poly_args.push(self.determine_inference_type_from_parser_type_elements(embedded_elements, true));
+        }
         // Handle the arguments and return types
         let definition = &ctx.heap[call.definition];
         let (parameters, returned) = match definition {
             Definition::Component(definition) => {
                 debug_assert_eq!(poly_args.len(), definition.poly_vars.len());
                 (&definition.parameters, None)
             },
             Definition::Function(definition) => {
                 debug_assert_eq!(poly_args.len(), definition.poly_vars.len());
                 (&definition.parameters, Some(&definition.return_type))
             },
             Definition::Struct(_) | Definition::Enum(_) | Definition::Union(_) => {
                 unreachable!("insert_initial_call_polymorph data for non-procedure type");
             },
         };
         let mut parameter_types = Vec::with_capacity(parameters.len());
         for parameter_id in parameters.clone().into_iter() { // TODO: @Performance @Now
             let param = &ctx.heap[parameter_id];
             parameter_types.push(self.determine_inference_type_from_parser_type_elements(&param.parser_type.elements, false));
+        }
         let return_type = match returned {
             None => {
                 // Component, so returns a "Void"
                 InferenceType::new(false, true, vec![InferenceTypePart::Void])
             },
             Some(returned) => {
                 self.determine_inference_type_from_parser_type_elements(&returned.elements, false)
+            }
         };
         self.extra_data[extra_data_idx as usize] = ExtraData{
         let extra_data_idx = self.extra_data.len() as ExtraIndex;
         self.extra_data.push(ExtraData{
             expr_id: call_id.upcast(),
             definition_id: call.definition,
             poly_vars: poly_args,
             embedded: parameter_types,
             returned: return_type
         };
         });
         return extra_data_idx
+    }
     fn insert_initial_struct_polymorph_data(
         &mut self, ctx: &mut Ctx, lit_id: LiteralExpressionId,
     ) {
+    ) -> ExtraIndex {
         use InferenceTypePart as ITP;
         let literal = &ctx.heap[lit_id];
         let extra_data_idx = self.expr_types[literal.unique_id_in_definition as usize].extra_data_idx; // TODO: @Temp
         debug_assert!(extra_data_idx != -1, "initial struct polymorph data, but no preallocated ExtraData");
         let literal = ctx.heap[lit_id].value.as_struct();
         // Handle polymorphic arguments
         let num_embedded = literal.parser_type.elements[0].variant.num_embedded();
         let mut total_num_poly_parts = 0;
         let mut poly_args = Vec::with_capacity(num_embedded);
         for embedded_elements in literal.parser_type.iter_embedded(0) {
             let poly_type = self.determine_inference_type_from_parser_type_elements(embedded_elements, true);
             total_num_poly_parts += poly_type.parts.len();
             poly_args.push(poly_type);
+        }
         // Handle parser types on struct definition
         let defined_type = ctx.types.get_base_definition(&literal.definition).unwrap();
         let struct_type = defined_type.definition.as_struct();
         debug_assert_eq!(poly_args.len(), defined_type.poly_vars.len());
         // Note: programmer is capable of specifying fields in a struct literal
         // in a different order than on the definition. We take the literal-
         // specified order to be leading.
         let mut embedded_types = Vec::with_capacity(struct_type.fields.len());
         for lit_field in literal.fields.iter() {
             let def_field = &struct_type.fields[lit_field.field_idx];
             let inference_type = self.determine_inference_type_from_parser_type_elements(&def_field.parser_type.elements, false);
             embedded_types.push(inference_type);
+        }
         // Return type is the struct type itself, with the appropriate
         // polymorphic variables. So:
         // - 1 part for definition
         // - N_poly_arg marker parts for each polymorphic argument
         // - all the parts for the currently known polymorphic arguments
         let parts_reserved = 1 + poly_args.len() + total_num_poly_parts;
         let mut parts = Vec::with_capacity(parts_reserved);
         parts.push(ITP::Instance(literal.definition, poly_args.len() as u32));
         let mut return_type_done = true;
         for (poly_var_idx, poly_var) in poly_args.iter().enumerate() {
             if !poly_var.is_done { return_type_done = false; }
             parts.push(ITP::Marker(poly_var_idx as u32));
             parts.extend(poly_var.parts.iter().cloned());
+        }
         debug_assert_eq!(parts.len(), parts_reserved);
         let return_type = InferenceType::new(!poly_args.is_empty(), return_type_done, parts);
         self.extra_data[extra_data_idx as usize] = ExtraData{
         let extra_data_index = self.extra_data.len() as ExtraIndex;
         self.extra_data.push(ExtraData{
             expr_id: lit_id.upcast(),
             definition_id: literal.definition,
             poly_vars: poly_args,
             embedded: embedded_types,
             returned: return_type,
         };
         });
         return extra_data_index
+    }
     /// Inserts the extra polymorphic data struct for enum expressions. These
     /// can never be determined from the enum itself, but may be inferred from
     /// the use of the enum.
     fn insert_initial_enum_polymorph_data(
         &mut self, ctx: &Ctx, lit_id: LiteralExpressionId
     ) {
+    ) -> ExtraIndex {
         use InferenceTypePart as ITP;
         let literal = &ctx.heap[lit_id];
         let extra_data_idx = self.expr_types[literal.unique_id_in_definition as usize].extra_data_idx; // TODO: @Temp
         debug_assert!(extra_data_idx != -1, "initial enum polymorph data, but no preallocated ExtraData");
         let literal = ctx.heap[lit_id].value.as_enum();
         // Handle polymorphic arguments to the enum
         let num_poly_args = literal.parser_type.elements[0].variant.num_embedded();
         let mut total_num_poly_parts = 0;
         let mut poly_args = Vec::with_capacity(num_poly_args);
         for embedded_elements in literal.parser_type.iter_embedded(0) {
             let poly_type = self.determine_inference_type_from_parser_type_elements(embedded_elements, true);
             total_num_poly_parts += poly_type.parts.len();
             poly_args.push(poly_type);
+        }
         // Handle enum type itself
         let parts_reserved = 1 + poly_args.len() + total_num_poly_parts;
         let mut parts = Vec::with_capacity(parts_reserved);
         parts.push(ITP::Instance(literal.definition, poly_args.len() as u32));
         let mut enum_type_done = true;
         for (poly_var_idx, poly_var) in poly_args.iter().enumerate() {
             if !poly_var.is_done { enum_type_done = false; }
             parts.push(ITP::Marker(poly_var_idx as u32));
             parts.extend(poly_var.parts.iter().cloned());
+        }
         debug_assert_eq!(parts.len(), parts_reserved);
         let enum_type = InferenceType::new(!poly_args.is_empty(), enum_type_done, parts);
         self.extra_data[extra_data_idx as usize] = ExtraData{
         let extra_data_index = self.extra_data.len() as ExtraIndex;
         self.extra_data.push(ExtraData{
             expr_id: lit_id.upcast(),
             definition_id: literal.definition,
             poly_vars: poly_args,
             embedded: Vec::new(),
             returned: enum_type,
         };
         });
         return extra_data_index;
+    }
     /// Inserts the extra polymorphic data struct for unions. The polymorphic
     /// arguments may be partially determined from embedded values in the union.
     fn insert_initial_union_polymorph_data(
         &mut self, ctx: &Ctx, lit_id: LiteralExpressionId
     ) {
         use InferenceTypePart as ITP;
         let literal = &ctx.heap[lit_id];
         let extra_data_idx = self.expr_types[literal.unique_id_in_definition as usize].extra_data_idx; // TODO: @Temp
         debug_assert!(extra_data_idx != -1, "initial union polymorph data, but no preallocated ExtraData");
         let literal = ctx.heap[lit_id].value.as_union();
         // Construct the polymorphic variables
         let num_poly_args = literal.parser_type.elements[0].variant.num_embedded();
         let mut total_num_poly_parts = 0;
         let mut poly_args = Vec::with_capacity(num_poly_args);
         for embedded_elements in literal.parser_type.iter_embedded(0) {
             let poly_type = self.determine_inference_type_from_parser_type_elements(embedded_elements, true);
             total_num_poly_parts += poly_type.parts.len();
             poly_args.push(poly_type);
+        }
         // Handle any of the embedded values in the variant, if specified
         let definition_id = literal.definition;
         let type_definition = ctx.types.get_base_definition(&definition_id).unwrap();
         let union_definition = type_definition.definition.as_union();
         debug_assert_eq!(poly_args.len(), type_definition.poly_vars.len());
         let variant_definition = &union_definition.variants[literal.variant_idx];
         debug_assert_eq!(variant_definition.embedded.len(), literal.values.len());
         let mut embedded = Vec::with_capacity(variant_definition.embedded.len());
         for embedded_parser_type in &variant_definition.embedded {
             let inference_type = self.determine_inference_type_from_parser_type_elements(&embedded_parser_type.elements, false);
             embedded.push(inference_type);
+        }
         // Handle the type of the union itself
         let parts_reserved = 1 + poly_args.len() + total_num_poly_parts;
         let mut parts = Vec::with_capacity(parts_reserved);
         parts.push(ITP::Instance(definition_id, poly_args.len() as u32));
         let mut union_type_done = true;
         for (poly_var_idx, poly_var) in poly_args.iter().enumerate() {
             if !poly_var.is_done { union_type_done = false; }
             parts.push(ITP::Marker(poly_var_idx as u32));
             parts.extend(poly_var.parts.iter().cloned());
+        }
         debug_assert_eq!(parts_reserved, parts.len());
         let union_type = InferenceType::new(!poly_args.is_empty(), union_type_done, parts);
         self.extra_data[extra_data_idx as usize] = ExtraData{
         let extra_data_index = self.extra_data.len();
         self.extra_data.push(ExtraData{
             expr_id: lit_id.upcast(),
             definition_id: literal.definition,
             poly_vars: poly_args,
             embedded,
             returned: union_type
         };
+        });
+    }
     /// Inserts the extra polymorphic data struct. Assumes that the select
     /// expression's referenced (definition_id, field_idx) has been resolved.
     fn insert_initial_select_polymorph_data(
         &mut self, ctx: &Ctx, select_id: SelectExpressionId, struct_def_id: DefinitionId
     ) {
+    ) -> ExtraIndex {
         use InferenceTypePart as ITP;
         // Retrieve relevant data
         let expr = &ctx.heap[select_id];
-        let expr_type = &self.expr_types[expr.unique_id_in_definition as usize];
+        let expr_type = &self.infer_nodes[expr.unique_id_in_definition as usize];
         let field_idx = expr_type.field_or_monomorph_idx as usize;
         let extra_data_idx = expr_type.extra_data_idx; // TODO: @Temp
         debug_assert!(extra_data_idx != -1, "initial select polymorph data, but no preallocated ExtraData");
         let definition = ctx.heap[struct_def_id].as_struct();
         // Generate initial polyvar types and struct type
         // TODO: @Performance: we can immediately set the polyvars of the subject's struct type
         let num_poly_vars = definition.poly_vars.len();
         let mut poly_vars = Vec::with_capacity(num_poly_vars);
         let struct_parts_reserved = 1 + 2 * num_poly_vars;
         let mut struct_parts = Vec::with_capacity(struct_parts_reserved);
         struct_parts.push(ITP::Instance(struct_def_id, num_poly_vars as u32));
         for poly_idx in 0..num_poly_vars {
             poly_vars.push(InferenceType::new(true, false, vec![
                 ITP::Marker(poly_idx as u32), ITP::Unknown,
             ]));
             struct_parts.push(ITP::Marker(poly_idx as u32));
             struct_parts.push(ITP::Unknown);
+        }
         debug_assert_eq!(struct_parts.len(), struct_parts_reserved);
         // Generate initial field type
         let field_type = self.determine_inference_type_from_parser_type_elements(&definition.fields[field_idx].parser_type.elements, false);
         self.extra_data[extra_data_idx as usize] = ExtraData{
         let extra_data_index = self.extra_data.len() as ExtraIndex;
         self.extra_data.push(ExtraData{
             expr_id: select_id.upcast(),
             definition_id: struct_def_id,
             poly_vars,
             embedded: vec![InferenceType::new(num_poly_vars != 0, num_poly_vars == 0, struct_parts)],
             returned: field_type
         };
         });
         return extra_data_index;
+    }
     /// Determines the initial InferenceType from the provided ParserType. This
     /// may be called with two kinds of intentions:
     /// 1. To resolve a ParserType within the body of a function, or on
     ///     polymorphic arguments to calls/instantiations within that body. This
     ///     means that the polymorphic variables are known and can be replaced
     ///     with the monomorph we're instantiating.
     /// 2. To resolve a ParserType on a called function's definition or on
     ///     an instantiated datatype's members. This means that the polymorphic
     ///     arguments inside those ParserTypes refer to the polymorphic
     ///     variables in the called/instantiated type's definition.
     /// In the second case we place InferenceTypePart::Marker instances such
     /// that we can perform type inference on the polymorphic variables.
     fn determine_inference_type_from_parser_type_elements(
         &mut self, elements: &[ParserTypeElement],
         use_definitions_known_poly_args: bool
     ) -> InferenceType {
         use ParserTypeVariant as PTV;
         use InferenceTypePart as ITP;
         let mut infer_type = Vec::with_capacity(elements.len());
         let mut has_inferred = false;
         let mut has_markers = false;
@@ @@ -3824,99 +4027,99 @@ impl PassTyping { @@
                 CTP::Input => parser_type.push(ITP::Input),
                 CTP::Output => parser_type.push(ITP::Output),
                 CTP::Pointer => unreachable!("pointer type during concrete to inference type conversion"),
                 CTP::Tuple(num) => parser_type.push(ITP::Tuple(*num)),
                 CTP::Instance(id, num) => parser_type.push(ITP::Instance(*id, *num)),
                 CTP::Function(_, _) => unreachable!("function type during concrete to inference type conversion"),
                 CTP::Component(_, _) => unreachable!("component type during concrete to inference type conversion"),
+            }
+        }
+    }
     /// Construct an error when an expression's type does not match. This
     /// happens if we infer the expression type from its arguments (e.g. the
     /// expression type of an addition operator is the type of the arguments)
     /// But the expression type was already set due to our parent (e.g. an
     /// "if statement" or a "logical not" always expecting a boolean)
     fn construct_expr_type_error(
         &self, ctx: &Ctx, expr_id: ExpressionId, arg_id: ExpressionId
     ) -> ParseError {
         // TODO: Expand and provide more meaningful information for humans
         let expr = &ctx.heap[expr_id];
         let arg_expr = &ctx.heap[arg_id];
         let expr_idx = expr.get_unique_id_in_definition();
         let arg_expr_idx = arg_expr.get_unique_id_in_definition();
         let expr_type = &self.expr_types[expr_idx as usize].expr_type;
         let arg_type = &self.expr_types[arg_expr_idx as usize].expr_type;
         let expr_type = &self.infer_nodes[expr_idx as usize].expr_type;
         let arg_type = &self.infer_nodes[arg_expr_idx as usize].expr_type;
         return ParseError::new_error_at_span(
             &ctx.module().source, expr.operation_span(), format!(
                 "incompatible types: this expression expected a '{}'",
                 expr_type.display_name(&ctx.heap)
+            )
         ).with_info_at_span(
             &ctx.module().source, arg_expr.full_span(), format!(
                 "but this expression yields a '{}'",
                 arg_type.display_name(&ctx.heap)
+            )
+        )
+    }
     fn construct_arg_type_error(
         &self, ctx: &Ctx, expr_id: ExpressionId,
         arg1_id: ExpressionId, arg2_id: ExpressionId
     ) -> ParseError {
         let expr = &ctx.heap[expr_id];
         let arg1 = &ctx.heap[arg1_id];
         let arg2 = &ctx.heap[arg2_id];
         let arg1_idx = arg1.get_unique_id_in_definition();
-        let arg1_type = &self.expr_types[arg1_idx as usize].expr_type;
+        let arg1_type = &self.infer_nodes[arg1_idx as usize].expr_type;
         let arg2_idx = arg2.get_unique_id_in_definition();
-        let arg2_type = &self.expr_types[arg2_idx as usize].expr_type;
+        let arg2_type = &self.infer_nodes[arg2_idx as usize].expr_type;
         return ParseError::new_error_str_at_span(
             &ctx.module().source, expr.operation_span(),
             "incompatible types: cannot apply this expression"
         ).with_info_at_span(
             &ctx.module().source, arg1.full_span(), format!(
                 "Because this expression has type '{}'",
                 arg1_type.display_name(&ctx.heap)
+            )
         ).with_info_at_span(
             &ctx.module().source, arg2.full_span(), format!(
                 "But this expression has type '{}'",
                 arg2_type.display_name(&ctx.heap)
+            )
+        )
+    }
     fn construct_template_type_error(
         &self, ctx: &Ctx, expr_id: ExpressionId, template: &[InferenceTypePart]
     ) -> ParseError {
         let expr = &ctx.heap[expr_id];
         let expr_idx = expr.get_unique_id_in_definition();
-        let expr_type = &self.expr_types[expr_idx as usize].expr_type;
+        let expr_type = &self.infer_nodes[expr_idx as usize].expr_type;
         return ParseError::new_error_at_span(
             &ctx.module().source, expr.full_span(), format!(
                 "incompatible types: got a '{}' but expected a '{}'",
                 expr_type.display_name(&ctx.heap),
                 InferenceType::partial_display_name(&ctx.heap, template)
+            )
+        )
+    }
     /// Constructs a human interpretable error in the case that type inference
     /// on a polymorphic variable to a function call or literal construction
     /// failed. This may only be caused by a pair of inference types (which may
     /// come from arguments or the return type) having two different inferred
     /// values for that polymorphic variable.
     ///
     /// So we find this pair and construct the error using it.
     ///
     /// We assume that the expression is a function call or a struct literal,
     /// and that an actual error has occurred.
     fn construct_poly_arg_error(
         ctx: &Ctx, poly_data: &ExtraData, expr_id: ExpressionId
     ) -> ParseError {
         // Helper function to check for polymorph mismatch between two inference

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