CSY/reowolf Changeset - f79a98e9e2d9 · Centrum Wiskunde & Informatica (CWI)

Changeset - f79a98e9e2d9

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mh - 3 years ago 2022-02-22 16:32:29
contact@maxhenger.nl

WIP: Replaced old expr-based with new rule-based inferencing code

1 file changed with 481 insertions and 68 deletions:

src/protocol/parser/pass_typing.rs

481

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src/protocol/parser/pass_typing.rs

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@@ @@ -801,24 +801,25 @@ impl DualInferenceResult { @@
 enum SingleInferenceResult {
     Unmodified,
     Modified,
     Incompatible
+}
 // -----------------------------------------------------------------------------
 // PassTyping - Public Interface
 // -----------------------------------------------------------------------------
 type InferNodeIndex = usize;
 type PolyDataIndex = usize;
 type VarDataIndex = usize;
 enum DefinitionType{
     Component(ComponentDefinitionId),
     Function(FunctionDefinitionId),
+}
 impl DefinitionType {
     fn definition_id(&self) -> DefinitionId {
         match self {
             DefinitionType::Component(v) => v.upcast(),
             DefinitionType::Function(v) => v.upcast(),
+        }
@@ @@ -876,24 +877,27 @@ impl InferenceRule { @@
     union_cast_method_impl!(as_bi_equal, InferenceRuleBiEqual, InferenceRule::BiEqual);
     union_cast_method_impl!(as_tri_equal_args, InferenceRuleTriEqualArgs, InferenceRule::TriEqualArgs);
     union_cast_method_impl!(as_tri_equal_all, InferenceRuleTriEqualAll, InferenceRule::TriEqualAll);
     union_cast_method_impl!(as_concatenate, InferenceRuleTwoArgs, InferenceRule::Concatenate);
     union_cast_method_impl!(as_indexing_expr, InferenceRuleIndexingExpr, InferenceRule::IndexingExpr);
     union_cast_method_impl!(as_slicing_expr, InferenceRuleSlicingExpr, InferenceRule::SlicingExpr);
     union_cast_method_impl!(as_select_struct_field, InferenceRuleSelectStructField, InferenceRule::SelectStructField);
     union_cast_method_impl!(as_select_tuple_member, InferenceRuleSelectTupleMember, InferenceRule::SelectTupleMember);
     union_cast_method_impl!(as_literal_struct, InferenceRuleLiteralStruct, InferenceRule::LiteralStruct);
     union_cast_method_impl!(as_literal_union, InferenceRuleLiteralUnion, InferenceRule::LiteralUnion);
     union_cast_method_impl!(as_literal_array, InferenceRuleLiteralArray, InferenceRule::LiteralArray);
     union_cast_method_impl!(as_literal_tuple, InferenceRuleLiteralTuple, InferenceRule::LiteralTuple);
     union_cast_method_impl!(as_cast_expr, InferenceRuleCastExpr, InferenceRule::CastExpr);
     union_cast_method_impl!(as_call_expr, InferenceRuleCallExpr, InferenceRule::CallExpr);
     union_cast_method_impl!(as_variable_expr, InferenceRuleVariableExpr, InferenceRule::VariableExpr);
+}
 struct InferenceRuleTemplate {
     template: &'static [InferenceTypePart],
     application: InferenceRuleTemplateApplication,
+}
 impl InferenceRuleTemplate {
     fn new_none() -> Self {
         return Self{
             template: &[],
             application: InferenceRuleTemplateApplication::None,
@@ @@ -993,62 +997,59 @@ struct InferenceRuleLiteralTuple { @@
 struct InferenceRuleCastExpr {
     subject_index: InferNodeIndex,
+}
 struct InferenceRuleCallExpr {
     argument_indices: Vec<InferNodeIndex>
+}
 /// Data associated with a variable expression: an expression that reads the
 /// value from a variable.
 struct InferenceRuleVariableExpr {
     variable_index: InferNodeIndex,
+}
 /// Data associated with a variable: keeping track of all the variable
 /// expressions in which it is used.
 struct InferenceRuleVariable {
     used_at_indices: Vec<InferNodeIndex>,
     var_data_index: VarDataIndex, // shared variable information
+}
 /// 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>,
     // Temporary variables during construction of inference rulesr
     parent_index: Option<InferNodeIndex>,
     // Buffers for iteration over various types
     var_buffer: ScopedBuffer<VariableId>,
     expr_buffer: ScopedBuffer<ExpressionId>,
     stmt_buffer: ScopedBuffer<StatementId>,
     bool_buffer: ScopedBuffer<bool>,
     index_buffer: ScopedBuffer<usize>,
     poly_progress_buffer: ScopedBuffer<u32>,
     temp_type_parts: Vec<InferenceTypePart>,
     // 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
+    var_types: HashMap<VariableId, VarDataDeprecated>,            // types of variables
     infer_nodes: Vec<InferenceNode>,                     // will be transferred to type table at end
     poly_data: Vec<PolyData>,       // data for polymorph inference
     var_data: Vec<VarData>,
     // 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>,
+}
 /// Generic struct that is used to store inferred types associated with
 /// polymorphic types.
 struct PolyData {
     first_rule_application: bool,
     definition_id: DefinitionId, // the definition, only used for user feedback
     /// Inferred types of the polymorphic variables as they are written down
     /// at the type's definition.
     poly_vars: Vec<InferenceType>,
     /// Inferred types of associated types (e.g. struct fields, tuple members,
     /// function arguments). These types may depend on the polymorphic variables
     /// defined above.
     associated: Vec<InferenceType>,
     /// Inferred "returned" type (e.g. if a struct field is selected, then this
     /// contains the type of the selected field, for a function call it contains
     /// the return type). May depend on the polymorphic variables defined above.
     returned: InferenceType,
@@ @@ -1078,43 +1079,50 @@ impl PolyData { @@
             PolyDataTypeIndex::Returned => return &self.returned,
+        }
+    }
     fn get_type_mut(&mut self, index: PolyDataTypeIndex) -> &mut InferenceType {
         match index {
             PolyDataTypeIndex::Associated(index) => return &mut self.associated[index],
             PolyDataTypeIndex::Returned => return &mut self.returned,
+        }
+    }
+}
-struct VarData {
+struct VarDataDeprecated {
     /// Type of the variable
     var_type: InferenceType,
     /// VariableExpressions that use the variable
     used_at: Vec<ExpressionId>,
     /// For channel statements we link to the other variable such that when one
     /// channel's interior type is resolved, we can also resolve the other one.
     linked_var: Option<VariableId>,
+}
-impl VarData {
+impl VarDataDeprecated {
     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 }
+    }
+}
 struct VarData {
     var_id: VariableId,
     var_type: InferenceType,
     used_at: Vec<InferNodeIndex>, // of variable expressions
     linked_var: Option<VarDataIndex>,
+}
 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(),
             parent_index: None,
             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),
             poly_progress_buffer: ScopedBuffer::with_capacity(BUFFER_INIT_CAP_SMALL),
@@ @@ -1227,25 +1235,25 @@ impl PassTyping { @@
         debug_log!("{}", "-".repeat(50));
         // Reserve data for expression types
         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));
+            self.var_types.insert(param_id, VarDataDeprecated::new_local(var_type));
+        }
         section.forget();
         // Visit the body and all of its expressions
         let body_stmt_id = ctx.heap[id].body;
         self.parent_index = None;
         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);
@@ @@ -1268,25 +1276,25 @@ impl PassTyping { @@
         debug_log!("{}", "-".repeat(50));
         // Reserve data for expression types
         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));
+            self.var_types.insert(param_id, VarDataDeprecated::new_local(var_type));
+        }
         section.forget();
         // Visit all of the expressions within the body
         let body_stmt_id = ctx.heap[id].body;
         self.parent_index = None;
         self.visit_block_stmt(ctx, body_stmt_id)
+    }
     // Statements
     fn visit_stmt(&mut self, ctx: &mut Ctx, id: StatementId) -> VisitorResult {
@@ @@ -1305,45 +1313,62 @@ impl PassTyping { @@
         Ok(())
+    }
     fn visit_local_stmt(&mut self, ctx: &mut Ctx, id: LocalStatementId) -> VisitorResult {
         return visitor_recursive_local_impl!(self, &ctx.heap[id], ctx);
+    }
     fn visit_local_memory_stmt(&mut self, ctx: &mut Ctx, id: MemoryStatementId) -> VisitorResult {
         let memory_stmt = &ctx.heap[id];
         let initial_expr_id = memory_stmt.initial_expr;
         // Setup memory statement inference
         let local = &ctx.heap[memory_stmt.variable];
         let var_type = self.determine_inference_type_from_parser_type_elements(&local.parser_type.elements, true);
         self.var_types.insert(memory_stmt.variable, VarData::new_local(var_type));
         self.var_data.push(VarData{
             var_id: memory_stmt.variable,
             var_type,
             used_at: Vec::new(),
             linked_var: None,
         });
         // Process the initial value
         self.visit_assignment_expr(ctx, initial_expr_id)?;
         Ok(())
+    }
     fn visit_local_channel_stmt(&mut self, ctx: &mut Ctx, id: ChannelStatementId) -> VisitorResult {
         let channel_stmt = &ctx.heap[id];
         let from_var_index = self.var_data.len() as VarDataIndex;
         let to_var_index = from_var_index + 1;
         let from_local = &ctx.heap[channel_stmt.from];
         let from_var_type = self.determine_inference_type_from_parser_type_elements(&from_local.parser_type.elements, true);
         self.var_types.insert(from_local.this, VarData::new_channel(from_var_type, channel_stmt.to));
         self.var_data.push(VarData{
             var_id: channel_stmt.from,
             var_type: from_var_type,
             used_at: Vec::new(),
             linked_var: Some(to_var_index),
         });
         let to_local = &ctx.heap[channel_stmt.to];
         let to_var_type = self.determine_inference_type_from_parser_type_elements(&to_local.parser_type.elements, true);
         self.var_types.insert(to_local.this, VarData::new_channel(to_var_type, channel_stmt.from));
         self.var_data.push(VarData{
             var_id: channel_stmt.to,
             var_type: to_var_type,
             used_at: Vec::new(),
             linked_var: Some(from_var_index),
         });
         Ok(())
+    }
     fn visit_labeled_stmt(&mut self, ctx: &mut Ctx, id: LabeledStatementId) -> VisitorResult {
         let labeled_stmt = &ctx.heap[id];
         let substmt_id = labeled_stmt.body;
         self.visit_stmt(ctx, substmt_id)
+    }
     fn visit_if_stmt(&mut self, ctx: &mut Ctx, id: IfStatementId) -> VisitorResult {
         let if_stmt = &ctx.heap[id];
@@ @@ -1480,49 +1505,51 @@ impl PassTyping { @@
             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.parent_index = old_parent;
         self.progress_assignment_expr(ctx, id)
         self.progress_inference_rule_tri_equal_args(ctx, self_index)?;
         return Ok(self_index);
+    }
     fn visit_binding_expr(&mut self, ctx: &mut Ctx, id: BindingExpressionId) -> VisitExprResult {
         let upcast_id = id.upcast();
         let self_index = self.insert_initial_inference_node(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;
         let old_parent = self.parent_index.replace(self_index);
         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.parent_index = old_parent;
         self.progress_binding_expr(ctx, id)
         self.progress_inference_rule_tri_equal_args(ctx, self_index)?;
         return Ok(self_index);
+    }
     fn visit_conditional_expr(&mut self, ctx: &mut Ctx, id: ConditionalExpressionId) -> VisitExprResult {
         let upcast_id = id.upcast();
         let self_index = self.insert_initial_inference_node(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;
         let old_parent = self.parent_index.replace(self_index);
@@ @@ -1533,39 +1560,40 @@ impl PassTyping { @@
         // 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.parent_index = old_parent;
         self.progress_conditional_expr(ctx, id)
         self.progress_inference_rule_tri_equal_all(ctx, self_index)?;
         return Ok(self_index);
+    }
     fn visit_binary_expr(&mut self, ctx: &mut Ctx, id: BinaryExpressionId) -> VisitExprResult {
         use BinaryOperator as BO;
         let upcast_id = id.upcast();
         let self_index = self.insert_initial_inference_node(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;
-        let parent_index = self.parent_index.replace(self_index);
+        let old_parent = self.parent_index.replace(self_index);
         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),
@@ @@ -1595,25 +1623,26 @@ impl PassTyping { @@
             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.parent_index = old_parent;
         self.progress_binary_expr(ctx, id)
         self.progress_inference_rule(ctx, self_index)?;
         return Ok(self_index);
+    }
     fn visit_unary_expr(&mut self, ctx: &mut Ctx, id: UnaryExpressionId) -> VisitExprResult {
         use UnaryOperator as UO;
         let upcast_id = id.upcast();
         let self_index = self.insert_initial_inference_node(ctx, upcast_id)?;
         let unary_expr = &ctx.heap[id];
         let operation = unary_expr.operation;
         let arg_expr_id = unary_expr.expression;
@@ @@ -1626,88 +1655,102 @@ impl PassTyping { @@
             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.parent_index = old_parent;
         self.progress_unary_expr(ctx, id)
         self.progress_inference_rule_bi_equal(ctx, self_index)?;
         return Ok(self_index);
+    }
     fn visit_indexing_expr(&mut self, ctx: &mut Ctx, id: IndexingExpressionId) -> VisitExprResult {
         let upcast_id = id.upcast();
         let self_index = self.insert_initial_inference_node(ctx, upcast_id)?;
         let indexing_expr = &ctx.heap[id];
         let subject_expr_id = indexing_expr.subject;
         let index_expr_id = indexing_expr.index;
         let old_parent = self.parent_index.replace(self_index);
         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.parent_index = old_parent;
         self.progress_indexing_expr(ctx, id)
         self.progress_inference_rule_indexing_expr(ctx, self_index)?;
         return Ok(self_index);
+    }
     fn visit_slicing_expr(&mut self, ctx: &mut Ctx, id: SlicingExpressionId) -> VisitExprResult {
         let upcast_id = id.upcast();
         let self_index = self.insert_initial_inference_node(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;
         let old_parent = self.parent_index.replace(self_index);
         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.parent_index = old_parent;
         self.progress_slicing_expr(ctx, id)
         self.progress_inference_rule_slicing_expr(ctx, self_index)?;
         return Ok(self_index);
+    }
     fn visit_select_expr(&mut self, ctx: &mut Ctx, id: SelectExpressionId) -> VisitExprResult {
         let upcast_id = id.upcast();
         let self_index = self.insert_initial_inference_node(ctx, upcast_id)?;
         let select_expr = &ctx.heap[id];
         let subject_expr_id = select_expr.subject;
         let old_parent = self.parent_index.replace(self_index);
         let subject_index = self.visit_expr(ctx, subject_expr_id)?;
         let node = &mut self.infer_nodes[self_index];
         node.inference_rule = InferenceRule::SelectExpr(InferenceRuleSelectExpr{
         let inference_rule = match &ctx.heap[id].kind {
             SelectKind::StructField(field_identifier) =>
                 InferenceRule::SelectStructField(InferenceRuleSelectStructField{
                     subject_index,
         });
                     selected_field: field_identifier.clone(),
                 }),
             SelectKind::TupleMember(member_index) =>
                 InferenceRule::SelectTupleMember(InferenceRuleSelectTupleMember{
                     subject_index,
                     selected_index: *member_index,
                 }),
         };
         node.inference_rule = inference_rule;
         self.parent_index = old_parent;
         self.progress_select_expr(ctx, id)
         self.progress_inference_rule(ctx, self_index)?;
         return Ok(self_index);
+    }
     fn visit_literal_expr(&mut self, ctx: &mut Ctx, id: LiteralExpressionId) -> VisitExprResult {
         let upcast_id = id.upcast();
         let self_index = self.insert_initial_inference_node(ctx, upcast_id)?;
         let old_parent = self.parent_index.replace(self_index);
         let literal_expr = &ctx.heap[id];
         match &literal_expr.value {
             Literal::Null => {
                 let node = &mut self.infer_nodes[self_index];
@@ @@ -1751,27 +1794,25 @@ impl PassTyping { @@
                 node.inference_rule = InferenceRule::LiteralStruct(InferenceRuleLiteralStruct{
                     element_indices,
                 });
             },
             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
                 let extra_index = self.insert_initial_enum_polymorph_data(ctx, id);
                 let node = &mut self.infer_nodes[self_index];
                 node.poly_data_index = extra_index;
                 node.inference_rule = InferenceRule::LiteralEnum(InferenceRuleLiteralEnum{
                 });
                 node.inference_rule = InferenceRule::LiteralEnum;
             },
             Literal::Union(literal) => {
                 // May carry subexpressions and polymorphic arguments
                 let expr_ids = self.expr_buffer.start_section_initialized(literal.values.as_slice());
                 let extra_index = self.insert_initial_union_polymorph_data(ctx, id);
                 let mut expr_indices = self.index_buffer.start_section();
                 for expr_id in expr_ids.iter_copied() {
                     let expr_index = self.visit_expr(ctx, expr_id)?;
                     expr_indices.push(expr_index);
+                }
                 expr_ids.forget();
@@ @@ -1794,44 +1835,56 @@ impl PassTyping { @@
                 expr_ids.forget();
                 let element_indices = expr_indices.into_vec();
                 let node = &mut self.infer_nodes[self_index];
                 node.poly_data_index = extra_index;
                 node.inference_rule = InferenceRule::LiteralArray(InferenceRuleLiteralArray{
                     element_indices,
                 })
+            }
+        }
         self.parent_index = old_parent;
         self.progress_literal_expr(ctx, id)
         self.progress_inference_rule(ctx, self_index)?;
         return Ok(self_index);
+    }
     fn visit_cast_expr(&mut self, ctx: &mut Ctx, id: CastExpressionId) -> VisitExprResult {
         let upcast_id = id.upcast();
         let self_index = self.insert_initial_inference_node(ctx, upcast_id)?;
         let cast_expr = &ctx.heap[id];
         let subject_expr_id = cast_expr.subject;
         let old_parent = self.parent_index.replace(self_index);
         let subject_index = self.visit_expr(ctx, subject_expr_id)?;
         let node = &mut self.infer_nodes[self_index];
         node.inference_rule = InferenceRule::CastExpr(InferenceRuleCastExpr{
             subject_index,
         });
         self.parent_index = old_parent;
         self.progress_cast_expr(ctx, id)
         // The cast expression is a bit special at this point: the progression
         // function simply makes sure input/output types are compatible. But if
         // the programmer explicitly specified the output type, then we can
         // already perform that inference rule here.
+        {
             let specified_type = self.determine_inference_type_from_parser_type_elements(&cast_expr.to_type.elements, true);
             let _progress = self.apply_template_constraint(ctx, self_index, &specified_type.parts)?;
+        }
         self.progress_inference_rule_cast_expr(ctx, self_index)?;
         return Ok(self_index);
+    }
     fn visit_call_expr(&mut self, ctx: &mut Ctx, id: CallExpressionId) -> VisitExprResult {
         let upcast_id = id.upcast();
         let self_index = self.insert_initial_inference_node(ctx, upcast_id)?;
         let extra_index = self.insert_initial_call_polymorph_data(ctx, id);
         // By default we set the polymorph idx for calls to 0. If the call
         // refers to a non-polymorphic function, then it will be "monomorphed"
         // once, hence we end up pointing to the correct instance.
         self.infer_nodes[self_index].field_or_monomorph_index = 0;
@@ @@ -1847,53 +1900,76 @@ impl PassTyping { @@
             expr_indices.push(expr_index);
+        }
         expr_ids.forget();
         let argument_indices = expr_indices.into_vec();
         let node = &mut self.infer_nodes[self_index];
         node.poly_data_index = extra_index;
         node.inference_rule = InferenceRule::CallExpr(InferenceRuleCallExpr{
             argument_indices,
         });
         self.parent_index = old_parent;
         self.progress_call_expr(ctx, id)
         self.progress_inference_rule_call_expr(ctx, self_index)?;
         return Ok(self_index);
+    }
     fn visit_variable_expr(&mut self, ctx: &mut Ctx, id: VariableExpressionId) -> VisitExprResult {
         let upcast_id = id.upcast();
         self.insert_initial_inference_node(ctx, upcast_id)?;
+        let self_index = self.insert_initial_inference_node(ctx, upcast_id)?;
         let var_expr = &ctx.heap[id];
         debug_assert!(var_expr.declaration.is_some());
         let old_parent = self.parent_index.replace(self_index);
         // 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 mut var_data_index = None;
         for (index, var_data) in self.var_data.iter().enumerate() {
             if var_data.var_id == declaration.this {
                 var_data_index = Some(index);
                 break;
+            }
+        }
         let var_data_index = if let Some(var_data_index) = var_data_index {
             let var_data = &mut self.var_data[var_data_index];
             var_data.used_at.push(self_index);
             var_data_index
         } else {
             // If we're in a binding expression then it might the first time we
             // encounter the variable, so add a `VarData` entry.
             debug_assert_eq!(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{
             let var_data_index = self.var_data.len();
             self.var_data.push(VarData{
                 var_id: declaration.this,
                 var_type,
                 used_at: vec![upcast_id],
                 linked_var: None
                 used_at: vec![self_index],
                 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)
             var_data_index
         };
         let node = &mut self.infer_nodes[self_index];
         node.inference_rule = InferenceRule::VariableExpr(InferenceRuleVariableExpr{
             var_data_index,
         });
         self.parent_index = old_parent;
         self.progress_inference_rule_variable_expr(ctx, self_index)?;
         return Ok(self_index);
+    }
+}
 // -----------------------------------------------------------------------------
 // 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.infer_nodes[expr_idx as usize].expr_type;
@@ @@ -2091,24 +2167,78 @@ impl PassTyping { @@
             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_index,
                 type_id: infer_expr.type_id,
             });
+        }
         Ok(())
+    }
     fn progress_inference_rule(&mut self, ctx: &Ctx, node_index: InferNodeIndex) -> Result<(), ParseError> {
         use InferenceRule as IR;
         let node = &self.infer_nodes[node_index];
         match &node.inference_rule {
             IR::Noop =>
                 return Ok(()),
             IR::MonoTemplate(_) =>
                 self.progress_inference_rule_mono_template(ctx, node_index),
             IR::BiEqual(_) =>
                 self.progress_inference_rule_bi_equal(ctx, node_index),
             IR::TriEqualArgs(_) =>
                 self.progress_inference_rule_tri_equal_args(ctx, node_index),
             IR::TriEqualAll(_) =>
                 self.progress_inference_rule_tri_equal_all(ctx, node_index),
             IR::Concatenate(_) =>
                 self.progress_inference_rule_concatenate(ctx, node_index),
             IR::IndexingExpr(_) =>
                 self.progress_inference_rule_indexing_expr(ctx, node_index),
             IR::SlicingExpr(_) =>
                 self.progress_inference_rule_slicing_expr(ctx, node_index),
             IR::SelectStructField(_) =>
                 self.progress_inference_rule_select_struct_field(ctx, node_index),
             IR::SelectTupleMember(_) =>
                 self.progress_inference_rule_select_tuple_member(ctx, node_index),
             IR::LiteralStruct(_) =>
                 self.progress_inference_rule_literal_struct(ctx, node_index),
             IR::LiteralEnum =>
                 self.progress_inference_rule_literal_enum(ctx, node_index),
             IR::LiteralUnion(_) =>
                 self.progress_inference_rule_literal_union(ctx, node_index),
             IR::LiteralArray(_) =>
                 self.progress_inference_rule_literal_array(ctx, node_index),
             IR::LiteralTuple(_) =>
                 self.progress_inference_rule_literal_tuple(ctx, node_index),
             IR::CastExpr(_) =>
                 self.progress_inference_rule_cast_expr(ctx, node_index),
             IR::CallExpr(_) =>
                 self.progress_inference_rule_call_expr(ctx, node_index),
             IR::VariableExpr(_) =>
                 self.progress_inference_rule_variable_expr(ctx, node_index),
+        }
+    }
     fn progress_inference_rule_mono_template(&mut self, ctx: &Ctx, node_index: InferNodeIndex) -> Result<(), ParseError> {
         let node = &self.infer_nodes[node_index];
         let rule = node.inference_rule.as_mono_template();
         let progress = self.progress_template(ctx, node_index, rule.application, rule.template)?;
         if progress { self.queue_node_parent(node_index); }
         return Ok(());
+    }
     fn progress_inference_rule_bi_equal(&mut self, ctx: &Ctx, node_index: InferNodeIndex) -> Result<(), ParseError> {
         let node = &self.infer_nodes[node_index];
         let rule = node.inference_rule.as_bi_equal();
         let arg_index = rule.argument_index;
         let base_progress = self.progress_template(ctx, node_index, rule.template.application, rule.template.template)?;
         let (node_progress, arg_progress) = self.apply_equal2_constraint(ctx, node_index, node_index, 0, arg_index, 0)?;
         if base_progress || node_progress { self.queue_node_parent(node_index); }
         if arg_progress { self.queue_node(arg_index); }
         return Ok(())
@@ @@ -2139,25 +2269,25 @@ impl PassTyping { @@
         let template_progress = self.progress_template(ctx, node_index, rule.template.application, rule.template.template)?;
         let (node_progress, arg1_progress, arg2_progress) =
             self.apply_equal3_constraint(ctx, node_index, arg1_index, arg2_index, 0)?;
         if template_progress || node_progress { self.queue_node_parent(node_index); }
         if arg1_progress { self.queue_node(arg1_index); }
         if arg2_progress { self.queue_node(arg2_index); }
         return Ok(());
+    }
-    fn progress_inference_rule_concatenate(&mut self, ctx: &mut Ctx, node_index: InferNodeIndex) -> Result<(), ParseError> {
     fn progress_inference_rule_concatenate(&mut self, ctx: &Ctx, node_index: InferNodeIndex) -> Result<(), ParseError> {
         let node = &self.infer_nodes[node_index];
         let rule = node.inference_rule.as_concatenate();
         let arg1_index = rule.argument1_index;
         let arg2_index = rule.argument2_index;
         // Two cases: one of the arguments is a string (then all must be), or
         // one of the arguments is an array (and all must be arrays).
         let (expr_is_str, expr_is_not_str) = self.type_is_certainly_or_certainly_not_string(node_index);
         let (arg1_is_str, arg1_is_not_str) = self.type_is_certainly_or_certainly_not_string(arg1_index);
         let (arg2_is_str, arg2_is_not_str) = self.type_is_certainly_or_certainly_not_string(arg2_index);
         let someone_is_str = expr_is_str || arg1_is_str || arg2_is_str;
@@ @@ -2261,25 +2391,25 @@ impl PassTyping { @@
                 subject_progress
+            )
         };
         if node_progress { self.queue_node_parent(node_index); }
         if subject_template_progress || subject_progress { self.queue_node(subject_index); }
         if from_template_progress || from_index_progress { self.queue_node(from_index_index); }
         if to_template_progress || to_index_progress { self.queue_node(to_index_index); }
         return Ok(());
+    }
-    fn progress_inference_rule_select_struct_field(&mut self, ctx: &mut Ctx, node_index: InferNodeIndex) -> Result<(), ParseError> {
     fn progress_inference_rule_select_struct_field(&mut self, ctx: &Ctx, node_index: InferNodeIndex) -> Result<(), ParseError> {
         let node = &self.infer_nodes[node_index];
         let rule = node.inference_rule.as_select_struct_field();
         let subject_index = rule.subject_index;
         fn get_definition_id_from_inference_type(inference_type: &InferenceType) -> Result<Option<DefinitionId>, ()> {
             for part in inference_type.parts.iter() {
                 if part.is_marker() { continue; }
                 if !part.is_concrete() { break; }
                 if let InferenceTypePart::Instance(definition_id, _) = part {
                     return Ok(Some(*definition_id));
@@ @@ -2374,49 +2504,34 @@ impl PassTyping { @@
         // Maybe make progress on types due to inferred polymorphic variables
         let progress_subject_2 = self.apply_polydata_polyvar_constraint(
             ctx, node_index, PolyDataTypeIndex::Associated(0), subject_index, &poly_progress_section
         );
         let progress_field_2 = self.apply_polydata_polyvar_constraint(
             ctx, node_index, PolyDataTypeIndex::Returned, node_index, &poly_progress_section
         );
         if progress_subject_1 || progress_subject_2 { self.queue_node(subject_index); }
         if progress_field_1 || progress_field_2 { self.queue_node_parent(node_index); }
         poly_progress_section.forget();
+        self.finish_polydata_constraint(node_index);
         return Ok(())
+    }
-    fn progress_inference_rule_select_tuple_member(&mut self, ctx: &mut Ctx, node_index: InferNodeIndex) -> Result<(), ParseError> {
     fn progress_inference_rule_select_tuple_member(&mut self, ctx: &Ctx, node_index: InferNodeIndex) -> Result<(), ParseError> {
         let node = &self.infer_nodes[node_index];
         let rule = node.inference_rule.as_select_tuple_member();
         let subject_index = rule.subject_index;
         let tuple_member_index = rule.selected_index;
         fn get_tuple_size_from_inference_type(inference_type: &InferenceType) -> Result<Option<u32>, ()> {
             for part in &inference_type.parts {
                 if part.is_marker() { continue; }
                 if !part.is_concrete() { break; }
                 if let InferenceTypePart::Tuple(size) = part {
                     return Ok(Some(*size));
                 } else {
                     return Err(()); // not a tuple!
+                }
+            }
             return Ok(None);
+        }
         if node.field_or_monomorph_index < 0 {
             let subject_type = &self.infer_nodes[subject_index].expr_type;
             let tuple_size = get_tuple_size_from_inference_type(subject_type);
             let tuple_size = match tuple_size {
                 Ok(Some(tuple_size)) => {
                     tuple_size
                 },
                 Ok(None) => {
                     // We can't infer anything yet
                     return Ok(())
                 },
                 Err(()) => {
@@ @@ -2503,48 +2618,49 @@ impl PassTyping { @@
             if progress_field { self.queue_node(field_node_index); }
+        }
         let progress_literal_2 = self.apply_polydata_polyvar_constraint(
             ctx, node_index, PolyDataTypeIndex::Returned,
             node_index, &poly_progress_section
         );
         if progress_literal_1 || progress_literal_2 { self.queue_node_parent(node_index); }
         poly_progress_section.forget();
+        self.finish_polydata_constraint(node_index);
         return Ok(())
+    }
     fn progress_inference_rule_literal_enum(&mut self, ctx: &Ctx, node_index: InferNodeIndex) -> Result<(), ParseError> {
         let node = &self.infer_nodes[node_index];
         let rule = node.inference_rule.as_literal_enum();
         let mut poly_progress_section = self.poly_progress_buffer.start_section();
         // An enum literal type is simply, well, the enum's type. However, it
         // might still have polymorphic variables, hence the use of `PolyData`.
         let (_, progress_literal_1) = self.apply_polydata_equal2_constraint(
             ctx, node_index, node.expr_id, "enum literal's",
             PolyDataTypeIndex::Returned, 0, node_index, 0, &mut poly_progress_section
         )?;
         let progress_literal_2 = self.apply_polydata_polyvar_constraint(
             ctx, node_index, PolyDataTypeIndex::Returned, node_index, &poly_progress_section
         );
         if progress_literal_1 || progress_literal_2 { self.queue_node_parent(node_index); }
         poly_progress_section.forget();
         self.finish_polydata_constraint(node_index);
         return Ok(());
+    }
     fn progress_inference_rule_literal_union(&mut self, ctx: &Ctx, node_index: InferNodeIndex) -> Result<(), ParseError> {
         let node = &self.infer_nodes[node_index];
         let rule = node.inference_rule.as_literal_union();
         // Infer type of any embedded values in the union variant. At the same
         // time progress the polymorphic variables associated with the union.
         let mut poly_progress_section = self.poly_progress_buffer.start_section();
         for (embedded_index, embedded_node_index) in rule.element_indices.iter().copied().enumerate() {
@@ @@ -2572,24 +2688,25 @@ impl PassTyping { @@
             );
             if progress_embedded { self.queue_node(embedded_node_index); }
+        }
         let progress_literal_2 = self.apply_polydata_polyvar_constraint(
             ctx, node_index, PolyDataTypeIndex::Returned, node_index, &poly_progress_section
         );
         if progress_literal_1 || progress_literal_2 { self.queue_node_parent(node_index); }
         poly_progress_section.forget();
         self.finish_polydata_constraint(node_index);
         return Ok(());
+    }
     fn progress_inference_rule_literal_array(&mut self, ctx: &Ctx, node_index: InferNodeIndex) -> Result<(), ParseError> {
         let node = &self.infer_nodes[node_index];
         let rule = node.inference_rule.as_literal_array();
         // Apply equality rule to all of the elements that form the array
         let argument_node_indices = self.index_buffer.start_section_initialized(&rule.element_indices);
         let mut argument_progress_section = self.bool_buffer.start_section();
         self.apply_equal_n_constraint(ctx, node_index, &argument_node_indices, &mut argument_progress_section)?;
@@ @@ -2619,24 +2736,267 @@ impl PassTyping { @@
         argument_node_indices.forget();
         argument_progress_section.forget();
         if progress_literal { self.queue_node_parent(node_index); }
         return Ok(());
+    }
     fn progress_inference_rule_literal_tuple(&mut self, ctx: &Ctx, node_index: InferNodeIndex) -> Result<(), ParseError> {
         let node = &self.infer_nodes[node_index];
         let rule = node.inference_rule.as_literal_tuple();
         let element_indices = self.index_buffer.start_section_initialized(&rule.element_indices);
         // Check if we need to apply the initial tuple template type. Note that
         // this is a hacky check.
         let num_tuple_elements = rule.element_indices.len();
         let mut template_type = Vec::with_capacity(num_tuple_elements + 1); // TODO: @performance
         template_type.push(InferenceTypePart::Tuple(num_tuple_elements as u32));
         for _ in 0..num_tuple_elements {
             template_type.push(InferenceTypePart::Unknown);
+        }
         let mut progress_literal = self.apply_template_constraint(ctx, node_index, &template_type)?;
         // Because of the (early returning error) check above, we're certain
         // that the tuple has the correct number of elements. Now match each
         // element expression type to the tuple subtype.
         let mut element_subtree_start_index = 1; // first element is InferenceTypePart::Tuple
         for element_node_index in element_indices.iter_copied() {
             let (progress_literal_element, progress_element) = self.apply_equal2_constraint(
                 ctx, node_index, node_index, element_subtree_start_index, element_node_index, 0
             )?;
             progress_literal = progress_literal || progress_literal_element;
             if progress_element {
                 self.queue_node(element_node_index);
+            }
             // Prepare for next element
             let subtree_end_index = InferenceType::find_subtree_end_idx(&node.expr_type.parts, element_subtree_start_index);
             element_subtree_start_index = subtree_end_index;
+        }
         debug_assert_eq!(element_subtree_end_index, node.expr_type.parts.len());
         if progress_literal { self.queue_node_parent(node_index); }
         element_indices.forget();
         return Ok(());
+    }
     fn progress_inference_rule_cast_expr(&mut self, ctx: &Ctx, node_index: InferNodeIndex) -> Result<(), ParseError> {
         let node = &self.infer_nodes[node_index];
         let rule = node.inference_rule.as_cast_expr();
         let subject_index = rule.subject_index;
         let subject = &self.infer_nodes[subject_index];
         // Make sure that both types are completely done. Note: a cast
         // expression cannot really infer anything between the subject and the
         // output type, we can only make sure that, at the end, the cast is
         // correct.
         if !node.expr_type.is_done || !subject.expr_type.is_done {
             return Ok(());
+        }
         // Both types are known, currently the only valid casts are bool,
         // integer and character casts.
         fn is_bool_int_or_char(parts: &[InferenceTypePart]) -> bool {
             let mut index = 0;
             while index < parts.len() {
                 let part = &parts[index];
                 if !part.is_marker() { break; }
                 index += 1;
+            }
             debug_assert!(index != parts.len());
             let part = &parts[index];
             if (
                 *part == InferenceTypePart::Bool ||
                 *part == InferenceTypePart::Character ||
                 part.is_concrete_integer()
             ) {
                 debug_assert!(index + 1 == parts.len()); // type is done, first part does not have children -> must be at end
                 return true;
             } else {
                 return false;
+            }
+        }
         let is_valid = if is_bool_int_or_char(&node.expr_type.parts) && is_bool_int_or_char(&subject.expr_type.parts) {
             true
         } else if InferenceType::check_subtrees(&node.expr_type.parts, 0, &subject.expr_type.parts, 0) {
             // again: check_subtrees is sufficient since both types are done
             true
         } else {
             false
         };
         if !is_valid {
             let cast_expr = &ctx.heap[node.expr_id];
             let subject_expr = &ctx.heap[subject.expr_id];
             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 type '{}'",
                     subject.expr_type.display_name(&ctx.heap),
                     node.expr_type.display_name(&ctx.heap)
+                )
             ));
+        }
         return Ok(())
+    }
     fn progress_inference_rule_call_expr(&mut self, ctx: &Ctx, node_index: InferNodeIndex) -> Result<(), ParseError> {
         let node = &self.infer_nodes[node_index];
         let rule = node.inference_rule.as_call_expr();
         let mut poly_progress_section = self.poly_progress_buffer.start_section();
         let argument_node_indices = self.index_buffer.start_section_initialized(&rule.argument_indices);
         // Perform inference on arguments to function, while trying to figure
         // out the polymorphic variables
         for (argument_index, argument_node_index) in argument_node_indices.iter_copied().enumerate() {
             let argument_expr_id = self.infer_nodes[argument_node_index].expr_id;
             let (_, progress_argument) = self.apply_polydata_equal2_constraint(
                 ctx, node_index, argument_expr_id, "argument's",
                 PolyDataTypeIndex::Associated(argument_index), 0,
                 argument_node_index, 0, &mut poly_progress_section
             )?;
             if progress_argument { self.queue_node(argument_node_index); }
+        }
         // Same for the return type.
         let call_expr_id = node.expr_id;
         let (_, progress_call_1) = self.apply_polydata_equal2_constraint(
             ctx, node_index, call_expr_id, "return",
             PolyDataTypeIndex::Returned, 0,
             node_index, 0, &mut poly_progress_section
         )?;
         // We will now apply any progression in the polymorphic variable type
         // back to the arguments.
         for (argument_index, argument_node_index) in argument_node_indices.iter_copied().enumerate() {
             let progress_argument = self.apply_polydata_polyvar_constraint(
                 ctx, node_index, PolyDataTypeIndex::Associated(argument_index),
                 argument_node_index, &poly_progress_section
             );
             if progress_argument { self.queue_node(argument_node_index); }
+        }
         // And back to the return type.
         let progress_call_2 = self.apply_polydata_polyvar_constraint(
             ctx, node_index, PolyDataTypeIndex::Returned,
             node_index, &poly_progress_section
         );
         if progress_call_1 || progress_call_2 { self.queue_node_parent(node_index); }
         poly_progress_section.forget();
         argument_node_indices.forget();
         self.finish_polydata_constraint(node_index);
         return Ok(())
+    }
     fn progress_inference_rule_variable_expr(&mut self, ctx: &Ctx, node_index: InferNodeIndex) -> Result<(), ParseError> {
         let node = &mut self.infer_nodes[node_index];
         let rule = node.inference_rule.as_variable_expr();
         let var_data_index = rule.var_data_index;
         let var_data = &mut self.var_data[var_data_index];
         // Apply inference to the shared variable type and the expression type
         let shared_type: *mut _ = &mut var_data.var_type;
         let expr_type: *mut _ = &mut node.expr_type;
         let inference_result = unsafe {
             // safety: vectors exist in different storage vectors, so cannot alias
             InferenceType::infer_subtrees_for_both_types(shared_type, 0, expr_type, 0)
         };
         if inference_result == DualInferenceResult::Incompatible {
             return Err(self.construct_variable_type_error(ctx, node_index));
+        }
         let progress_var_data = inference_result.modified_lhs();
         let progress_expr = inference_result.modified_rhs();
         if progress_var_data {
             // We progressed the type of the shared variable, so propagate this
             // to all associated variable expressions (and relatived variables).
             for other_node_index in var_data.used_at.iter().copied() {
                 if other_node_index != node_index {
                     self.queue_node(other_node_index);
+                }
+            }
             if let Some(linked_var_data_index) = var_data.linked_var {
                 // Only perform one-way inference, progressing the linked
                 // variable.
                 // note: because this "linking" is used only for channels, we
                 // will start inference one level below the top-level in the
                 // type tree (i.e. ensure `T` in `in<T>` and `out<T>` is equal).
                 debug_assert!(
                     var_data.var_type.parts[0] == InferenceTypePart::Input ||
                     var_data.var_type.parts[0] == InferenceTypePart::Output
                 );
                 let this_var_type: *const _ = &var_data.var_type;
                 let linked_var_data = &mut self.var_data[linked_var_data_index];
                 debug_assert!(
                     linked_var_data.var_type.parts[0] == InferenceTypePart::Input ||
                     linked_var_data.var_type.parts[0] == InferenceTypePart::Output
                 );
                 // safety: by construction var_data_index and linked_var_data_index cannot be the
                 // same, hence we're not aliasing here.
                 let inference_result = InferenceType::infer_subtree_for_single_type(
                     &mut linked_var_data.var_type, 1,
                     unsafe{ &(*this_var_type).parts }, 1, false
                 );
                 match inference_result {
                     SingleInferenceResult::Modified => {
                         for used_at in linked_var_data.used_at.iter().copied() {
                             self.queue_node(used_at);
+                        }
                     },
                     SingleInferenceResult::Unmodified => {},
                     SingleInferenceResult::Incompatible => {
                         let var_data_this = &self.var_data[var_data_index];
                         let var_decl_this = &ctx.heap[var_data_this.var_id];
                         let var_data_linked = &self.var_data[linked_var_data_index];
                         let var_decl_linked = &ctx.heap[var_data_linked.var_id];
                         return Err(ParseError::new_error_at_span(
                             &ctx.module().source, var_decl_this.identifier.span, format!(
                                 "conflicting types for this channel, this port has type '{}'",
                                 var_data_this.var_type.display_name(&ctx.heap)
+                            )
                         ).with_info_at_span(
                             &ctx.module().source, var_decl_linked.identifier.span, format!(
                                 "while this port has type '{}'",
                                 var_data_linked.var_type.display_name(&ctx.heap)
+                            )
                         ));
+                    }
+                }
+            }
+        }
         if progress_expr { self.queue_node_parent(node_index); }
         return Ok(());
+    }
     fn progress_template(&mut self, ctx: &Ctx, node_index: InferNodeIndex, application: InferenceRuleTemplateApplication, template: &[InferenceTypePart]) -> Result<bool, ParseError> {
         use InferenceRuleTemplateApplication as TA;
         match application {
             TA::None => Ok(false),
             TA::Template => self.apply_template_constraint(ctx, node_index, template),
             TA::Forced => self.apply_forced_constraint(ctx, node_index, template),
+        }
+    }
@@ @@ -4002,25 +4362,25 @@ impl PassTyping { @@
         ) };
         if infer_res == DualInferenceResult::Incompatible {
             return Err(self.construct_arg_type_error(ctx, node_index, arg1_index, arg2_index));
+        }
         Ok((infer_res.modified_lhs(), infer_res.modified_rhs()))
+    }
     /// Applies an equal2 constraint between a member of the `PolyData` struct,
     /// and another inferred type. If any progress is made in the `PolyData`
     /// struct then the affected polymorphic variables are updated as well.
     ///
-    /// Because a lot of types/expressions are involved in polymorphic type
+    /// Because a lot of types/expressions are involved in polymorphic typFe
     /// inference, some explanation: "outer_node" refers to the main expression
     /// that is the root cause of type inference (e.g. a struct literal
     /// expression, or a tuple member select expression). Associated with that
     /// outer node is `PolyData`, so that is what the "poly_data" variables
     /// are referring to. We are applying equality between a "poly_data" type
     /// and an associated expression (not necessarily the "outer_node", e.g.
     /// the expression that constructs the value of a struct field). Hence the
     /// "associated" variables.
     ///
     /// Finally, when an error occurs we'll first show the outer node's
     /// location. As info, the `error_location_expr_id` span is shown,
     /// indicating that the "`error_type_name` type has been resolved to
@@ @@ -4115,32 +4475,39 @@ impl PassTyping { @@
     /// the appropriate type in the `PolyData` struct. Which will be updated
     /// first using the polymorphic variables. If we happen to have updated that
     /// type, then we should also progress the associated expression, hence the
     /// `associated_node_index`.
     fn apply_polydata_polyvar_constraint(
         &mut self, ctx: &Ctx,
         outer_node_index: InferNodeIndex, poly_data_type_index: PolyDataTypeIndex,
         associated_node_index: InferNodeIndex, poly_progress_section: &ScopedSection<u32>
     ) -> bool {
         let poly_data_index = self.infer_nodes[outer_node_index].poly_data_index;
         let poly_data = &mut self.poly_data[poly_data_index];
         // Early exit, most common case (literals or functions calls which are
         // actually not polymorphic)
         if !poly_data.first_rule_application && poly_progress_section.len() == 0 {
             return false;
+        }
         // safety: we're borrowing from two distinct fields, so should be fine
         let poly_data_type = poly_data.get_type_mut(poly_data_type_index);
         let mut last_start_index = 0;
         let mut modified_poly_type = false;
         while let Some((poly_var_index, poly_var_start_index)) = poly_data_type.find_marker(last_start_index) {
             let poly_var_end_index = InferenceType::find_subtree_end_idx(&poly_data_type.parts, poly_var_start_index);
             if poly_progress_section.contains(&poly_var_index) {
             if poly_data.first_rule_application || poly_progress_section.contains(&poly_var_index) {
                 // We have updated this polymorphic variable, so try updating it
                 // in the PolyData type
                 let modified_in_poly_data = match InferenceType::infer_subtree_for_single_type(
                     poly_data_type, poly_var_start_index, &poly_data.poly_vars[poly_var_index as usize].parts, 0, false
                 ) {
                     SingleInferenceResult::Modified => true,
                     SingleInferenceResult::Unmodified => false,
                     SingleInferenceResult::Incompatible => {
                         // practically impossible: before calling this function we gather all the
                         // data on the polymorphic variables from the associated expressions. So if
                         // the polymorphic variables in those expressions were not mutually
                         // compatible, we must have encountered that error already.
@@ @@ -4160,24 +4527,32 @@ impl PassTyping { @@
                 associated_type, 0, &poly_data_type.parts, 0, true
             ) {
                 SingleInferenceResult::Modified => return true,
                 SingleInferenceResult::Unmodified => return false,
                 SingleInferenceResult::Incompatible => unreachable!(), // same as above
+            }
         } else {
             // Did not update associated type
             return false;
+        }
+    }
     /// Should be called after completing one full round of applying polydata
     /// constraints.
     fn finish_polydata_constraint(&mut self, outer_node_index: InferNodeIndex) {
         let poly_data_index = self.infer_nodes[outer_node_index].poly_data_index;
         let poly_data = &mut self.poly_data[poly_data_index];
         poly_data.first_rule_application = false;
+    }
     /// 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 PolyData, polymorph_progress: &mut HashSet<u32>,
@@ @@ -4951,24 +5326,47 @@ impl PassTyping { @@
         let expr = &ctx.heap[node.expr_id];
         let expr_type = &node.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)
+            )
+        )
+    }
     fn construct_variable_type_error(
         &self, ctx: &Ctx, node_index: InferNodeIndex,
     ) -> ParseError {
         let node = &self.infer_nodes[node_index];
         let rule = node.inference_rule.as_variable_expr();
         let var_data = &self.var_data[rule.var_data_index];
         let var_decl = &ctx.heap[var_data.var_id];
         let var_expr = &ctx.heap[node.expr_id];
         return 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.full_span(), format!(
                 "but inferred to have incompatible type '{}' here",
                 node.expr_type.display_name(&ctx.heap)
+            )
         );
+    }
     /// 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: &PolyData, expr_id: ExpressionId
@@ @@ -5185,24 +5583,39 @@ impl PassTyping { @@
                         "The polymorphic variable has type '{}' (which might have been partially inferred) while the {} inferred it to '{}'",
                         InferenceType::partial_display_name(&ctx.heap, poly_section),
                         expr_return_name,
                         InferenceType::partial_display_name(&ctx.heap, ret_section)
+                    )
+                )
+        }
         unreachable!("construct_poly_arg_error without actual error found?")
+    }
+}
 fn get_tuple_size_from_inference_type(inference_type: &InferenceType) -> Result<Option<u32>, ()> {
     for part in &inference_type.parts {
         if part.is_marker() { continue; }
         if !part.is_concrete() { break; }
         if let InferenceTypePart::Tuple(size) = part {
             return Ok(Some(*size));
         } else {
             return Err(()); // not a tuple!
+        }
+    }
     return Ok(None);
+}
 #[cfg(test)]
 mod tests {
     use super::*;
     use crate::protocol::arena::Id;
     use InferenceTypePart as ITP;
     use InferenceType as IT;
     #[test]
     fn test_single_part_inference() {
         // lhs argument inferred from rhs
         let pairs = [
             (ITP::NumberLike, ITP::UInt8),

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