CSY/reowolf Changeset - fb9fe040916a · Centrum Wiskunde & Informatica (CWI)

Changeset - fb9fe040916a

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MH - 4 years ago 2021-03-21 18:40:02
contact@maxhenger.nl

add helper for constructing polymorph infer errors

1 file changed with 170 insertions and 15 deletions:

src/protocol/parser/type_resolver.rs

170

0 comments (0 inline, 0 general)

src/protocol/parser/type_resolver.rs

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@@ @@ -490,193 +490,193 @@ impl InferenceType { @@
             if let Some(depth_change) = Self::check_part_for_single_type(
                 type_parts_a, &mut idx_a, type_parts_b, &mut idx_b
             ) {
                 depth += depth_change;
                 continue;
+            }
             if let Some(depth_change) = Self::check_part_for_single_type(
                 type_parts_b, &mut idx_b, type_parts_a, &mut idx_a
             ) {
                 depth += depth_change;
                 continue;
+            }
             return false;
+        }
         true
+    }
     /// Returns a human-readable version of the type. Only use for debugging
     /// or returning errors (since it allocates a string).
     fn write_display_name(
         buffer: &mut String, heap: &Heap, parts: &[InferenceTypePart], mut idx: usize
     ) -> usize {
         use InferenceTypePart as ITP;
         match &parts[idx] {
             ITP::Marker(_) => {},
             ITP::Unknown => buffer.push_str("?"),
             ITP::NumberLike => buffer.push_str("num?"),
             ITP::IntegerLike => buffer.push_str("int?"),
             ITP::ArrayLike => {
                 idx = Self::write_display_name(buffer, heap, parts, idx + 1);
                 buffer.push_str("[?]");
             },
             ITP::PortLike => {
                 buffer.push_str("port?<");
                 idx = Self::write_display_name(buffer, heap, parts, idx + 1);
                 buffer.push('>');
+            }
             ITP::Void => buffer.push_str("void"),
             ITP::Message => buffer.push_str("msg"),
             ITP::Bool => buffer.push_str("bool"),
             ITP::Byte => buffer.push_str("byte"),
             ITP::Short => buffer.push_str("short"),
             ITP::Int => buffer.push_str("int"),
             ITP::Long => buffer.push_str("long"),
             ITP::String => buffer.push_str("str"),
             ITP::Array => {
                 idx = Self::write_display_name(buffer, heap, parts, idx + 1);
                 buffer.push_str("[]");
             },
             ITP::Slice => {
                 idx = Self::write_display_name(buffer, heap, parts, idx + 1);
                 buffer.push_str("[..]");
             },
             ITP::Input => {
                 buffer.push_str("in<");
                 idx = Self::write_display_name(buffer, heap, parts, idx + 1);
                 buffer.push('>');
             },
             ITP::Output => {
                 buffer.push_str("out<");
                 idx = Self::write_display_name(buffer, heap, parts, idx + 1);
                 buffer.push('>');
             },
             ITP::Instance(definition_id, num_sub) => {
                 let definition = &heap[*definition_id];
                 buffer.push_str(&String::from_utf8_lossy(&definition.identifier().value));
                 if *num_sub > 0 {
                     buffer.push('<');
                     idx = Self::write_display_name(buffer, heap, parts, idx + 1);
                     for _sub_idx in 1..*num_sub {
                         buffer.push_str(", ");
                         idx = Self::write_display_name(buffer, heap, parts, idx + 1);
+                    }
                     buffer.push('>');
+                }
             },
+        }
         idx
+    }
     fn partial_display_name(heap: &Heap, parts: &[InferenceTypePart]) -> String {
         let mut buffer = String::with_capacity(parts.len() * 6);
         Self::write_display_name(&mut buffer, heap, parts, 0);
         buffer
+    }
     fn display_name(&self, heap: &Heap) -> String {
         Self::partial_display_name(heap, &self.parts)
+    }
+}
 /// Iterator over the subtrees that follow a marker in an `InferenceType`
 /// instance
+/// instance.
 struct InferenceTypeMarkerIter<'a> {
     parts: &'a [InferenceTypePart],
     idx: usize,
+}
 impl<'a> InferenceTypeMarkerIter<'a> {
     fn new(parts: &'a [InferenceTypePart]) -> Self {
         Self{ parts, idx: 0 }
+    }
+}
 impl<'a> Iterator for InferenceTypeMarkerIter<'a> {
     type Item = (usize, &'a [InferenceTypePart]);
     fn next(&mut self) -> Option<Self::Item> {
         // Iterate until we find a marker
         while self.idx < self.parts.len() {
             if let InferenceTypePart::Marker(marker) = self.parts[self.idx] {
                 // Found a marker, find the subtree end
                 let start_idx = self.idx + 1;
                 let end_idx = InferenceType::find_subtree_end_idx(self.parts, start_idx);
                 // Modify internal index, then return items
                 self.idx = end_idx;
                 return Some((marker, &self.parts[start_idx..end_idx]))
+            }
             self.idx += 1;
+        }
         None
+    }
+}
 #[derive(PartialEq, Eq)]
 enum DualInferenceResult {
     Neither,        // neither argument is clarified
     First,          // first argument is clarified using the second one
     Second,         // second argument is clarified using the first one
     Both,           // both arguments are clarified
     Incompatible,   // types are incompatible: programmer error
+}
 impl DualInferenceResult {
     fn modified_any(&self) -> bool {
         match self {
             DualInferenceResult::First | DualInferenceResult::Second | DualInferenceResult::Both => true,
             _ => false
+        }
+    }
     fn modified_lhs(&self) -> bool {
         match self {
             DualInferenceResult::First | DualInferenceResult::Both => true,
             _ => false
+        }
+    }
     fn modified_rhs(&self) -> bool {
         match self {
             DualInferenceResult::Second | DualInferenceResult::Both => true,
             _ => false
+        }
+    }
+}
 #[derive(PartialEq, Eq)]
 enum SingleInferenceResult {
     Unmodified,
     Modified,
     Incompatible
+}
 enum DefinitionType{
     None,
     Component(ComponentId),
     Function(FunctionId),
+}
 /// This particular visitor will recurse depth-first into the AST and ensures
 /// that all expressions have the appropriate types. At the moment this implies:
 ///
 ///     - Type checking arguments to unary and binary operators.
 ///     - Type checking assignment, indexing, slicing and select expressions.
 ///     - Checking arguments to functions and component instantiations.
 ///
 /// This will be achieved by slowly descending into the AST. At any given
 /// expression we may depend on
 pub(crate) struct TypeResolvingVisitor {
     definition_type: DefinitionType,
     // Buffers for iteration over substatements and subexpressions
     stmt_buffer: Vec<StatementId>,
     expr_buffer: Vec<ExpressionId>,
     // If instantiating a monomorph of a polymorphic proctype, then we store the
     // values of the polymorphic values here. There should be as many, and in
     // the same order as, in the definition's polyargs.
@@ @@ -1099,271 +1099,274 @@ impl TypeResolvingVisitor { @@
                     self.apply_equal3_constraint(ctx, upcast_id, arg1_id, arg2_id, 0)?;
                 (progress_base || progress_expr, progress_base || progress_arg1, progress_base || progress_arg2)
             },
         };
         if progress_expr { self.queue_expr_parent(ctx, upcast_id); }
         if progress_arg1 { self.queue_expr(arg1_id); }
         if progress_arg2 { self.queue_expr(arg2_id); }
         Ok(())
+    }
     fn progress_unary_expr(&mut self, ctx: &mut Ctx, id: UnaryExpressionId) -> Result<(), ParseError2> {
         use UnaryOperation as UO;
         let upcast_id = id.upcast();
         let expr = &ctx.heap[id];
         let arg_id = expr.expression;
         let (progress_expr, progress_arg) = match expr.operation {
             UO::Positive | UO::Negative => {
                 // Equal types of numeric class
                 let progress_base = self.apply_forced_constraint(ctx, upcast_id, &NUMBERLIKE_TEMPLATE)?;
                 let (progress_expr, progress_arg) =
                     self.apply_equal2_constraint(ctx, upcast_id, upcast_id, 0, arg_id, 0)?;
                 (progress_base || progress_expr, progress_base || progress_arg)
             },
             UO::BitwiseNot | UO::PreIncrement | UO::PreDecrement | UO::PostIncrement | UO::PostDecrement => {
                 // Equal types of integer class
                 let progress_base = self.apply_forced_constraint(ctx, upcast_id, &INTEGERLIKE_TEMPLATE)?;
                 let (progress_expr, progress_arg) =
                     self.apply_equal2_constraint(ctx, upcast_id, upcast_id, 0, arg_id, 0)?;
                 (progress_base || progress_expr, progress_base || progress_arg)
             },
             UO::LogicalNot => {
                 // Both booleans
                 let progress_expr = self.apply_forced_constraint(ctx, upcast_id, &BOOL_TEMPLATE)?;
                 let progress_arg = self.apply_forced_constraint(ctx, upcast_id, &BOOL_TEMPLATE)?;
                 (progress_expr, progress_arg)
+            }
         };
         if progress_expr { self.queue_expr_parent(ctx, upcast_id); }
         if progress_arg { self.queue_expr(arg_id); }
         Ok(())
+    }
     fn progress_indexing_expr(&mut self, ctx: &mut Ctx, id: IndexingExpressionId) -> Result<(), ParseError2> {
         let upcast_id = id.upcast();
         let expr = &ctx.heap[id];
         let subject_id = expr.subject;
         let index_id = expr.index;
         // Make sure subject is arraylike and index is integerlike
         let progress_subject_base = self.apply_forced_constraint(ctx, subject_id, &ARRAYLIKE_TEMPLATE)?;
         let progress_index = self.apply_forced_constraint(ctx, index_id, &INTEGERLIKE_TEMPLATE)?;
         // Make sure if output is of T then subject is Array<T>
         let (progress_expr, progress_subject) =
             self.apply_equal2_constraint(ctx, upcast_id, upcast_id, 0, subject_id, 1)?;
         if progress_expr { self.queue_expr_parent(ctx, upcast_id); }
         if progress_subject_base || progress_subject { self.queue_expr(subject_id); }
         if progress_index { self.queue_expr(index_id); }
         Ok(())
+    }
     fn progress_slicing_expr(&mut self, ctx: &mut Ctx, id: SlicingExpressionId) -> Result<(), ParseError2> {
         let upcast_id = id.upcast();
         let expr = &ctx.heap[id];
         let subject_id = expr.subject;
         let from_id = expr.from_index;
         let to_id = expr.to_index;
         // Make sure subject is arraylike and indices are of equal integerlike
         let progress_subject_base = self.apply_forced_constraint(ctx, subject_id, &ARRAYLIKE_TEMPLATE)?;
         let progress_idx_base = self.apply_forced_constraint(ctx, from_id, &INTEGERLIKE_TEMPLATE)?;
         let (progress_from, progress_to) = self.apply_equal2_constraint(ctx, upcast_id, from_id, 0, to_id, 0)?;
         // Make sure if output is of T then subject is Array<T>
         let (progress_expr, progress_subject) =
             self.apply_equal2_constraint(ctx, upcast_id, upcast_id, 0, subject_id, 1)?;
         if progress_expr { self.queue_expr_parent(ctx, upcast_id); }
         if progress_subject_base || progress_subject { self.queue_expr(subject_id); }
         if progress_idx_base || progress_from { self.queue_expr(from_id); }
         if progress_idx_base || progress_to { self.queue_expr(to_id); }
         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<(), ParseError2> {
         let upcast_id = id.upcast();
         let expr = &ctx.heap[id];
         let extra = self.extra_data.get_mut(&upcast_id).unwrap();
         // 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());
         let mut poly_infer_error = false;
         for (arg_idx, arg_id) in expr.arguments.clone().into_iter().enumerate() {
             let signature_type = &mut extra.embedded[arg_idx];
             let argument_type: *mut _ = self.expr_types.get_mut(&arg_id).unwrap();
             let (progress_sig, progress_arg) = Self::apply_equal2_constraint_types(
                 ctx, upcast_id, signature_type, 0, argument_type, 0
             )?;
             if progress_sig {
                 // Progressed signature, so also apply inference to the
                 // polymorph types using the markers
                 debug_assert!(signature_type.has_marker, "progress on signature argument type without markers");
                 for (poly_idx, poly_section) in signature_type.marker_iter() {
                     let polymorph_type = &mut extra.poly_vars[poly_idx];
                     match Self::apply_forced_constraint_types(
                         ctx, upcast_id, polymorph_type, 0, poly_section, 0
                     ) {
                         Ok(true) => { poly_progress.insert(poly_idx); },
                         Ok(false) => {},
                         Err(()) => { poly_infer_error = true; }
+                    }
+                }
+            }
             if progress_arg {
                 // Progressed argument expression
                 self.queue_expr(arg_id);
+            }
+        }
         // Do the same for the return type
         let signature_type = &mut extra.returned;
         let expr_type: *mut _ = self.expr_types.get_mut(&upcast_id).unwrap();
         let (progress_sig, progress_expr) = Self::apply_equal2_constraint_types(
             ctx, upcast_id, signature_type, 0, expr_type, 0
         )?;
         if progress_sig {
             // As above: apply inference to polyargs as well
             debug_assert!(signature_type.has_marker, "progress on signature return type without markers");
             for (poly_idx, poly_section) in signature_type.marker_iter() {
                 let polymorph_type = &mut extra.poly_vars[poly_idx];
                 match Self::apply_forced_constraint_types(
                     ctx, upcast_id, polymorph_type, 0, poly_section, 0
                 ) {
                     Ok(true) => { poly_progress.insert(poly_idx); },
                     Ok(false) => {},
                     Err(()) => { poly_infer_error = true; }
+                }
+            }
+        }
         if progress_expr {
             self.queue_expr_parent(ctx, upcast_id);
+        }
         // If we did not have an error in the polymorph progression (in the
         // current inefficient implementation), then this means that all types
         // still agree on the polymorphic variables.
         //
         // If we did have an error, then this means that a pair of (argument,
         // return type) did not agree on the inferred value of a single
         // polymorphic variable. Since this is an error case we do not care
         // about efficiency for now, we loop over all expressions, retrieve the
         // subtrees for the markers and see which ones differ (at least one pair
         // must differ!)
         // If we had an error in the polymorphic variable's inference, then we
         // need to provide a human readable error: find a pair of inference
         // types in the arguments/return type that do not agree on the
         // polymorphic variable's type
         if poly_infer_error { return Err(self.construct_poly_arg_error(ctx, id)) }
         // If we did not have an error, but we did expand the polymorphic
         // variables, then we need to re-expand these by insertion.
         let mut v = Vec::new();
         // 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.
         // 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 valid
         for poly_idx in poly_progress.into_iter() {
+        }
         Ok(())
+    }
     fn queue_expr_parent(&mut self, ctx: &Ctx, expr_id: ExpressionId) {
         if let ExpressionParent::Expression(parent_expr_id, _) = &ctx.heap[expr_id].parent() {
             self.expr_queued.insert(*parent_expr_id);
+        }
+    }
     fn queue_expr(&mut self, expr_id: ExpressionId) {
         self.expr_queued.insert(expr_id);
+    }
     /// Applies a forced type constraint: the type associated with the supplied
     /// expression will be molded into the provided "template". The template may
     /// be fully specified (e.g. a bool) or contain "inference" variables (e.g.
     /// an array of T)
     fn apply_forced_constraint(
         &mut self, ctx: &mut Ctx, expr_id: ExpressionId, template: &[InferenceTypePart]
     ) -> Result<bool, ParseError2> {
         debug_assert_expr_ids_unique_and_known!(self, expr_id);
         let expr_type = self.expr_types.get_mut(&expr_id).unwrap();
         match InferenceType::infer_subtree_for_single_type(expr_type, 0, template, 0) {
             SingleInferenceResult::Modified => Ok(true),
             SingleInferenceResult::Unmodified => Ok(false),
             SingleInferenceResult::Incompatible => Err(
                 self.construct_template_type_error(ctx, expr_id, template)
+            )
+        }
+    }
     fn apply_forced_constraint_types(
         ctx: &Ctx, expr_id: ExpressionId,
         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
         ) {
             SingleInferenceResult::Modified => Ok(true),
             SingleInferenceResult::Unmodified => Ok(false),
             SingleInferenceResult::Incompatible => Err(()),
+        }
+    }
     /// 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), ParseError2> {
         debug_assert_expr_ids_unique_and_known!(self, arg1_id, arg2_id);
         let arg1_type: *mut _ = self.expr_types.get_mut(&arg1_id).unwrap();
         let arg2_type: *mut _ = self.expr_types.get_mut(&arg2_id).unwrap();
         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()))
+    }
     fn apply_equal2_constraint_types(
         ctx: &Ctx, expr_id: ExpressionId,
         type1: *mut InferenceType, type1_start_idx: usize,
         type2: *mut InferenceType, type2_start_idx: usize
     ) -> Result<(bool, bool), ParseError2> {
         debug_assert_ptrs_distinct!(type1, type2);
         let infer_res = unsafe {
             InferenceType::infer_subtrees_for_both_types(
                 type1, type1_start_idx,
                 type2, type2_start_idx
+            )
         };
         if infer_res == DualInferenceResult::Incompatible {
             return Err(ParseError2::new_error(
                 &ctx.module.source, ctx.heap[expr_id].position(),
                 "TODO: Write me, apply_equal2_constraint_types"
             ));
+        }
         Ok((infer_res.modified_lhs(), infer_res.modified_rhs()))
+    }
     /// 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
@@ @@ -1447,193 +1450,193 @@ impl TypeResolvingVisitor { @@
                 },
             EP::New(_) =>
                 // Must be a component call, which we assign a "Void" return
                 // type
                 InferenceType::new(false, true, vec![ITP::Void]),
             EP::Put(_, 0) =>
                 // TODO: Change put to be a builtin function
                 // port of "put" call
                 InferenceType::new(false, false, vec![ITP::Output, ITP::Unknown]),
             EP::Put(_, 1) =>
                 // TODO: Change put to be a builtin function
                 // message of "put" call
                 InferenceType::new(false, true, vec![ITP::Message]),
             EP::Put(_, _) =>
                 unreachable!()
         };
         match self.expr_types.entry(expr_id) {
             Entry::Vacant(vacant) => {
                 vacant.insert(inference_type);
             },
             Entry::Occupied(mut preexisting) => {
                 // We already have an entry, this happens if our parent fixed
                 // our type (e.g. we're used in a conditional expression's test)
                 // but we have a different type.
                 // TODO: Is this ever called? Seems like it can't
                 debug_assert!(false, "I am actually called, my ID is {}", expr_id.index);
                 let old_type = preexisting.get_mut();
                 if let SingleInferenceResult::Incompatible = InferenceType::infer_subtree_for_single_type(
                     old_type, 0, &inference_type.parts, 0
                 ) {
                     return Err(self.construct_expr_type_error(ctx, expr_id, expr_id))
+                }
+            }
+        }
         Ok(())
+    }
     fn insert_initial_call_polymorph_data(
         &mut self, ctx: &mut Ctx, call_id: CallExpressionId
     ) {
         use InferenceTypePart as ITP;
         // 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];
         debug_assert!(!call.poly_args.is_empty());
         // Handle the polymorphic variables themselves
         let mut poly_vars = Vec::with_capacity(call.poly_args.len());
         for poly_arg_type_id in call.poly_args.clone() { // TODO: @performance
             poly_vars.push(self.determine_inference_type_from_parser_type(ctx, poly_arg_type_id, true));
+        }
         // Handle the arguments
         // TODO: @cleanup: Maybe factor this out for reuse in the validator/linker, should also
         //  make the code slightly more robust.
         let (embedded_types, return_type) = match &call.method {
             Method::Create => {
                 // Not polymorphic
                 unreachable!("insert initial polymorph data for builtin 'create()' call")
             },
             Method::Fires => {
                 // bool fires<T>(PortLike<T> arg)
+                (
                     vec![InferenceType::new(true, false, vec![ITP::PortLike, ITP::Marker(0), ITP::Unknown])],
                     InferenceType::new(false, true, vec![ITP::Bool])
+                )
             },
             Method::Get => {
                 // T get<T>(input<T> arg)
+                (
                     vec![InferenceType::new(true, false, vec![ITP::Input, ITP::Marker(0), ITP::Unknown])],
                     InferenceType::new(true, false, vec![ITP::Marker(0), ITP::Unknown])
+                )
             },
             Method::Symbolic(symbolic) => {
                 let definition = &ctx.heap[symbolic.definition.unwrap()];
                 match definition {
                     Definition::Component(definition) => {
                         let mut parameter_types = Vec::with_capacity(definition.parameters.len());
                         for param_id in definition.parameters.clone() {
                             let param = &ctx.heap[param_id];
                             let param_parser_type_id = param.parser_type;
                             parameter_types.push(self.determine_inference_type_from_parser_type(ctx, param_parser_type_id, false));
+                        }
-                        (parameter_types, InferenceType::new(false, true, vec![InferenceTypePart::Unknown]))
+                        (parameter_types, InferenceType::new(false, true, vec![InferenceTypePart::Void]))
                     },
                     Definition::Function(definition) => {
                         let mut parameter_types = Vec::with_capacity(definition.parameters.len());
                         for param_id in definition.parameters.clone() {
                             let param = &ctx.heap[param_id];
                             let param_parser_type_id = param.parser_type;
                             parameter_types.push(self.determine_inference_type_from_parser_type(ctx, param_parser_type_id, false));
+                        }
                         let return_type = self.determine_inference_type_from_parser_type(ctx, definition.return_type, false);
                         (parameter_types, return_type)
                     },
                     Definition::Struct(_) | Definition::Enum(_) => {
                         unreachable!("insert initial polymorph data for struct/enum");
+                    }
+                }
+            }
         };
         self.extra_data.insert(call_id.upcast(), ExtraData {
             poly_vars,
             embedded: embedded_types,
             returned: return_type
         });
+    }
     /// 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(
         &mut self, ctx: &Ctx, parser_type_id: ParserTypeId,
         parser_type_in_body: bool
     ) -> InferenceType {
         use ParserTypeVariant as PTV;
         use InferenceTypePart as ITP;
         let mut to_consider = VecDeque::with_capacity(16);
         to_consider.push_back(parser_type_id);
         let mut infer_type = Vec::new();
         let mut has_inferred = false;
         let mut has_markers = false;
         while !to_consider.is_empty() {
             let parser_type_id = to_consider.pop_front().unwrap();
             let parser_type = &ctx.heap[parser_type_id];
             match &parser_type.variant {
                 PTV::Message => { infer_type.push(ITP::Message); },
                 PTV::Bool => { infer_type.push(ITP::Bool); },
                 PTV::Byte => { infer_type.push(ITP::Byte); },
                 PTV::Short => { infer_type.push(ITP::Short); },
                 PTV::Int => { infer_type.push(ITP::Int); },
                 PTV::Long => { infer_type.push(ITP::Long); },
                 PTV::String => { infer_type.push(ITP::String); },
                 PTV::IntegerLiteral => { unreachable!("integer literal type on variable type"); },
                 PTV::Inferred => {
                     infer_type.push(ITP::Unknown);
                     has_inferred = true;
                 },
                 PTV::Array(subtype_id) => {
                     infer_type.push(ITP::Array);
                     to_consider.push_front(*subtype_id);
                 },
                 PTV::Input(subtype_id) => {
                     infer_type.push(ITP::Input);
                     to_consider.push_front(*subtype_id);
                 },
                 PTV::Output(subtype_id) => {
                     infer_type.push(ITP::Output);
                     to_consider.push_front(*subtype_id);
                 },
                 PTV::Symbolic(symbolic) => {
                     debug_assert!(symbolic.variant.is_some(), "symbolic variant not yet determined");
                     match symbolic.variant.unwrap() {
                         SymbolicParserTypeVariant::PolyArg(_, arg_idx) => {
                             // Retrieve concrete type of argument and add it to
                             // the inference type.
                             debug_assert!(symbolic.poly_args.is_empty()); // TODO: @hkt
                             if parser_type_in_body {
                                 debug_assert!(arg_idx < self.polyvars.len());
                                 for concrete_part in &self.polyvars[arg_idx].v {
                                     infer_type.push(ITP::from(*concrete_part));
+                                }
                             } else {
                                 has_markers = true;
                                 infer_type.push(ITP::Marker(arg_idx));
@@ @@ -1648,97 +1651,249 @@ impl TypeResolvingVisitor { @@
                                 let num_poly = match definition {
                                     Definition::Struct(v) => v.poly_vars.len(),
                                     Definition::Enum(v) => v.poly_vars.len(),
                                     _ => unreachable!(),
                                 };
                                 debug_assert_eq!(symbolic.poly_args.len(), num_poly);
+                            }
                             infer_type.push(ITP::Instance(definition_id, symbolic.poly_args.len()));
                             let mut poly_arg_idx = symbolic.poly_args.len();
                             while poly_arg_idx > 0 {
                                 poly_arg_idx -= 1;
                                 to_consider.push_front(symbolic.poly_args[poly_arg_idx]);
+                            }
+                        }
+                    }
+                }
+            }
+        }
         InferenceType::new(has_markers, !has_inferred, infer_type)
+    }
     /// 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
     ) -> ParseError2 {
         // TODO: Expand and provide more meaningful information for humans
         let expr = &ctx.heap[expr_id];
         let arg_expr = &ctx.heap[arg_id];
         let expr_type = self.expr_types.get(&expr_id).unwrap();
         let arg_type = self.expr_types.get(&arg_id).unwrap();
         return ParseError2::new_error(
             &ctx.module.source, expr.position(),
             &format!(
                 "Incompatible types: this expression expected a '{}'",
                 expr_type.display_name(&ctx.heap)
+            )
         ).with_postfixed_info(
             &ctx.module.source, arg_expr.position(),
             &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
     ) -> ParseError2 {
         let expr = &ctx.heap[expr_id];
         let arg1 = &ctx.heap[arg1_id];
         let arg2 = &ctx.heap[arg2_id];
         let arg1_type = self.expr_types.get(&arg1_id).unwrap();
         let arg2_type = self.expr_types.get(&arg2_id).unwrap();
         return ParseError2::new_error(
             &ctx.module.source, expr.position(),
             "Incompatible types: cannot apply this expression"
         ).with_postfixed_info(
             &ctx.module.source, arg1.position(),
             &format!(
                 "Because this expression has type '{}'",
                 arg1_type.display_name(&ctx.heap)
+            )
         ).with_postfixed_info(
             &ctx.module.source, arg2.position(),
             &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]
     ) -> ParseError2 {
         let expr = &ctx.heap[expr_id];
         let expr_type = self.expr_types.get(&expr_id).unwrap();
         return ParseError2::new_error(
             &ctx.module.source, expr.position(),
             &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 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 (which may be a argument type or return type
     /// conflicting with itself) and construct the error using it.
     fn construct_poly_arg_error(
         &self, ctx: &Ctx, call_id: CallExpressionId
     ) -> ParseError2 {
         // Helper function to check for polymorph mismatch between two inference
         // types.
         fn has_poly_mismatch<'a>(type_a: &'a InferenceType, type_b: &'a InferenceType) -> Option<(usize, &'a [InferenceTypePart], &'a [InferenceTypePart])> {
             if !type_a.has_marker || !type_b.has_marker {
                 return None
+            }
             for (marker_a, section_a) in type_a.marker_iter() {
                 for (marker_b, section_b) in type_b.marker_iter() {
                     if marker_a != marker_b {
                         // Not the same polymorphic variable
                         continue;
+                    }
                     if !InferenceType::check_subtrees(section_a, 0, section_b, 0) {
                         // Not compatible
                         return Some((marker_a, section_a, section_b))
+                    }
+                }
+            }
             None
+        }
         // Helpers function to retrieve polyvar name and function name
         fn get_poly_var_and_func_name(ctx: &Ctx, poly_var_idx: usize, expr: &CallExpression) -> (String, String) {
             let expr = &ctx.heap[call_id];
             match &expr.method {
                 Method::Create => unreachable!(),
                 Method::Fires => (String::from('T'), String::from("fires")),
                 Method::Get => (String::from('T'), String::from("get")),
                 Method::Symbolic(symbolic) => {
                     let definition = &ctx.heap[symbolic.definition.unwrap()];
                     let poly_var = match definition {
                         Definition::Struct(_) | Definition::Enum(_) => unreachable!(),
                         Definition::Function(definition) => {
                             String::from_utf8_lossy(&definition.poly_vars[poly_var_idx].value).to_string()
                         },
                         Definition::Component(definition) => {
                             String::from_utf8_lossy(&definition.poly_vars[poly_var_idx].value).to_string()
+                        }
                     };
                     let func_name = String::from_utf8_lossy(&symbolic.identifier.value).to_string();
                     (poly_var, func_name)
+                }
+            }
+        }
         // Helper function to construct initial error
         fn construct_main_error(ctx: &Ctx, poly_var_idx: usize, expr: &CallExpression) -> ParseError2 {
             let (poly_var, func_name) = get_poly_var_and_func_name(ctx, poly_var_idx, expr);
             return ParseError2::new_error(
                 &ctx.module.source, expr.position(),
                 &format!(
                     "Conflicting type for polymorphic variable '{}' of '{}'",
                     poly_var, func_name
+                )
+            )
+        }
         // Actual checking
         let extra = self.extra_data.get(&call_id.upcast()).unwrap();
         let expr = &ctx.heap[call_id];
         // - check return type with itself
         if let Some((poly_idx, section_a, section_b)) = has_poly_mismatch(&extra.returned, &extra.returned) {
             return construct_main_error(ctx, poly_idx, expr)
                 .with_postfixed_info(
                     &ctx.module.source, expr.position(),
                     &format!(
                         "The return type inferred the conflicting types '{}' and '{}'",
                         InferenceType::partial_display_name(heap, section_a),
                         InferenceType::partial_display_name(heap, section_b)
+                    )
+                )
+        }
         // - check arguments with each other argument and with return type
         for (arg_a_idx, arg_a) in extra.embedded.iter().enumerate() {
             for (arg_b_idx, arg_b) in extra.embedded.iter().enumerate() {
                 if arg_b_idx > arg_a_idx {
                     break;
+                }
                 if let Some((poly_idx, section_a, section_b)) = has_poly_mismatch(&arg_a, &arg_b) {
                     let error = construct_main_error(ctx, poly_idx, expr);
                     if arg_a_idx == arg_b_idx {
                         // Same argument
                         let arg = &ctx.heap[expr.arguments[arg_a_idx]];
                         return error.with_postfixed_info(
                             &ctx.module.source, arg.position(),
                             &format!(
                                 "This argument inferred the conflicting types '{}' and '{}'",
                                 InferenceType::partial_display_name(heap, section_a),
                                 InferenceType::partial_display_name(heap, section_b)
+                            )
+                        )
                     } else {
                         let arg_a = &ctx.heap[expr.arguments[arg_a_idx]];
                         let arg_b = &ctx.heap[expr.arguments[arg_b_idx]];
                         return error.with_postfixed_info(
                             &ctx.module.source, arg_a.position(),
                             &format!(
                                 "This argument inferred it to '{}'",
                                 InferenceType::partial_display_name(heap, section_a)
+                            )
                         ).with_postfixed_info(
                             &ctx.module.source, arg_b.position(),
                             &format!(
                                 "While this argument inferred it to '{}'",
                                 InferenceType::partial_display_name(heap, section_b)
+                            )
+                        )
+                    }
+                }
+            }
             // Check with return type
             if let Some((poly_idx, section_arg, section_ret)) = has_poly_mismatch(arg_a, &extra.returned) {
                 let arg = &ctx.heap[expr.arguments[arg_a_idx]];
                 return construct_main_error(ctx, poly_idx, expr)
                     .with_postfixed_info(
                         &ctx.module.source, arg.position(),
                         &format!(
                             "This argument inferred it to '{}'",
                             InferenceType::partial_display_name(heap, section_arg)
+                        )
+                    )
                     .with_postfixed_info(
                         &ctx.module.source, expr.position,
                         &format!(
                             "While the return type inferred it to '{}'",
                             InferenceType::partial_display_name(heap, section_ret)
+                        )
+                    )
+            }
+        }
         unreachable!("construct_poly_arg_error without actual error found?")
+    }
+}
@@ \ No newline at end of file @@

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