Changeset - fcf8c30ed335
[Not reviewed]
0 2 0
mh - 4 years ago 2021-04-30 10:32:36
contact@maxhenger.nl
WIP on fixing type inferencer
2 files changed with 209 insertions and 245 deletions:
0 comments (0 inline, 0 general)
src/protocol/ast.rs
Show inline comments
 
@@ -1522,95 +1522,106 @@ impl Expression {
 
    pub fn as_variable(&self) -> &VariableExpression {
 
        match self {
 
            Expression::Variable(result) => result,
 
            _ => panic!("Unable to cast `Expression` to `VariableExpression`"),
 
        }
 
    }
 
    pub fn as_variable_mut(&mut self) -> &mut VariableExpression {
 
        match self {
 
            Expression::Variable(result) => result,
 
            _ => panic!("Unable to cast `Expression` to `VariableExpression`"),
 
        }
 
    }
 
    pub fn span(&self) -> InputSpan {
 
        match self {
 
            Expression::Assignment(expr) => expr.span,
 
            Expression::Binding(expr) => expr.span,
 
            Expression::Conditional(expr) => expr.span,
 
            Expression::Binary(expr) => expr.span,
 
            Expression::Unary(expr) => expr.span,
 
            Expression::Indexing(expr) => expr.span,
 
            Expression::Slicing(expr) => expr.span,
 
            Expression::Select(expr) => expr.span,
 
            Expression::Literal(expr) => expr.span,
 
            Expression::Call(expr) => expr.span,
 
            Expression::Variable(expr) => expr.identifier.span,
 
        }
 
    }
 
    // TODO: @cleanup
 
    pub fn parent(&self) -> &ExpressionParent {
 
        match self {
 
            Expression::Assignment(expr) => &expr.parent,
 
            Expression::Binding(expr) => &expr.parent,
 
            Expression::Conditional(expr) => &expr.parent,
 
            Expression::Binary(expr) => &expr.parent,
 
            Expression::Unary(expr) => &expr.parent,
 
            Expression::Indexing(expr) => &expr.parent,
 
            Expression::Slicing(expr) => &expr.parent,
 
            Expression::Select(expr) => &expr.parent,
 
            Expression::Array(expr) => &expr.parent,
 
            Expression::Literal(expr) => &expr.parent,
 
            Expression::Call(expr) => &expr.parent,
 
            Expression::Variable(expr) => &expr.parent,
 
        }
 
    }
 
    // TODO: @cleanup
 
    pub fn parent_expr_id(&self) -> Option<ExpressionId> {
 
        if let ExpressionParent::Expression(id, _) = self.parent() {
 
            Some(*id)
 
        } else {
 
            None
 
        }
 
    }
 
    // TODO: @cleanup
 
    pub fn set_parent(&mut self, parent: ExpressionParent) {
 
        match self {
 
            Expression::Assignment(expr) => expr.parent = parent,
 
            Expression::Binding(expr) => expr.parent = parent,
 
            Expression::Conditional(expr) => expr.parent = parent,
 
            Expression::Binary(expr) => expr.parent = parent,
 
            Expression::Unary(expr) => expr.parent = parent,
 
            Expression::Indexing(expr) => expr.parent = parent,
 
            Expression::Slicing(expr) => expr.parent = parent,
 
            Expression::Select(expr) => expr.parent = parent,
 
            Expression::Array(expr) => expr.parent = parent,
 
            Expression::Literal(expr) => expr.parent = parent,
 
            Expression::Call(expr) => expr.parent = parent,
 
            Expression::Variable(expr) => expr.parent = parent,
 
        }
 
    }
 
    pub fn get_type(&self) -> &ConcreteType {
 
        match self {
 
            Expression::Assignment(expr) => &expr.concrete_type,
 
            Expression::Binding(expr) => &expr.concrete_type,
 
            Expression::Conditional(expr) => &expr.concrete_type,
 
            Expression::Binary(expr) => &expr.concrete_type,
 
            Expression::Unary(expr) => &expr.concrete_type,
 
            Expression::Indexing(expr) => &expr.concrete_type,
 
            Expression::Slicing(expr) => &expr.concrete_type,
 
            Expression::Select(expr) => &expr.concrete_type,
 
            Expression::Array(expr) => &expr.concrete_type,
 
            Expression::Literal(expr) => &expr.concrete_type,
 
            Expression::Call(expr) => &expr.concrete_type,
 
            Expression::Variable(expr) => &expr.concrete_type,
 
        }
 
    }
 

	
 
    // TODO: @cleanup
 
    pub fn get_type_mut(&mut self) -> &mut ConcreteType {
 
        match self {
 
            Expression::Assignment(expr) => &mut expr.concrete_type,
 
            Expression::Binding(expr) => &mut expr.concrete_type,
 
            Expression::Conditional(expr) => &mut expr.concrete_type,
 
            Expression::Binary(expr) => &mut expr.concrete_type,
 
            Expression::Unary(expr) => &mut expr.concrete_type,
 
            Expression::Indexing(expr) => &mut expr.concrete_type,
 
            Expression::Slicing(expr) => &mut expr.concrete_type,
 
            Expression::Select(expr) => &mut expr.concrete_type,
 
            Expression::Array(expr) => &mut expr.concrete_type,
 
            Expression::Literal(expr) => &mut expr.concrete_type,
 
            Expression::Call(expr) => &mut expr.concrete_type,
 
            Expression::Variable(expr) => &mut expr.concrete_type,
 
        }
 
    }
 
}
 

	
 
#[derive(Debug, Clone)]
 
pub enum AssignmentOperator {
 
    Set,
 
    Multiplied,
 
    Divided,
src/protocol/parser/type_resolver.rs
Show inline comments
 
@@ -48,37 +48,39 @@
 
macro_rules! debug_log {
 
    ($format:literal) => {
 
        enabled_debug_print!(true, "types", $format);
 
    };
 
    ($format:literal, $($args:expr),*) => {
 
        enabled_debug_print!(true, "types", $format, $($args),*);
 
    };
 
}
 

	
 
use std::collections::{HashMap, HashSet, VecDeque};
 

	
 
use crate::protocol::ast::*;
 
use crate::protocol::inputsource::*;
 
use crate::protocol::input_source2::{InputSource2 as InputSource, ParseError};
 
use crate::protocol::parser::type_table::*;
 
use super::visitor::{
 
    STMT_BUFFER_INIT_CAPACITY,
 
    EXPR_BUFFER_INIT_CAPACITY,
 
    Ctx,
 
    Visitor2,
 
    VisitorResult
 
};
 
use std::collections::hash_map::Entry;
 

	
 
const MESSAGE_TEMPLATE: [InferenceTypePart; 2] = [ InferenceTypePart::Message, InferenceTypePart::Byte ];
 
const BOOL_TEMPLATE: [InferenceTypePart; 1] = [ InferenceTypePart::Bool ];
 
const CHARACTER_TEMPLATE: [InferenceTypePart; 1] = [ InferenceTypePart::Character ];
 
const STRING_TEMPLATE: [InferenceTypePart; 1] = [ InferenceTypePart::String ];
 
const NUMBERLIKE_TEMPLATE: [InferenceTypePart; 1] = [ InferenceTypePart::NumberLike ];
 
const INTEGERLIKE_TEMPLATE: [InferenceTypePart; 1] = [ InferenceTypePart::IntegerLike ];
 
const ARRAY_TEMPLATE: [InferenceTypePart; 2] = [ InferenceTypePart::Array, InferenceTypePart::Unknown ];
 
const ARRAYLIKE_TEMPLATE: [InferenceTypePart; 2] = [ InferenceTypePart::ArrayLike, InferenceTypePart::Unknown ];
 

	
 
/// TODO: @performance Turn into PartialOrd+Ord to simplify checks
 
/// TODO: @types Remove the Message -> Byte hack at some point...
 
#[derive(Debug, Clone, Eq, PartialEq)]
 
pub(crate) enum InferenceTypePart {
 
    // A marker with an identifier which we can use to retrieve the type subtree
 
    // that follows the marker. This is used to perform type inference on
 
    // polymorphs: an expression may determine the polymorphs type, after we
 
@@ -90,28 +92,33 @@ pub(crate) enum InferenceTypePart {
 
    Unknown,
 
    // Partially known type, may be inferred to to be the appropriate related 
 
    // type.
 
    // IndexLike,      // index into array/slice
 
    NumberLike,     // any kind of integer/float
 
    IntegerLike,    // any kind of integer
 
    ArrayLike,      // array or slice. Note that this must have a subtype
 
    PortLike,       // input or output port
 
    // Special types that cannot be instantiated by the user
 
    Void, // For builtin functions that do not return anything
 
    // Concrete types without subtypes
 
    Bool,
 
    Byte,
 
    Short,
 
    Int,
 
    Long,
 
    UInt8,
 
    UInt16,
 
    UInt32,
 
    UInt64,
 
    SInt8,
 
    SInt16,
 
    SInt32,
 
    SInt64,
 
    Character,
 
    String,
 
    // One subtype
 
    Message,
 
    Array,
 
    Slice,
 
    Input,
 
    Output,
 
    // A user-defined type with any number of subtypes
 
    Instance(DefinitionId, usize)
 
}
 

	
 
impl InferenceTypePart {
 
@@ -242,25 +249,25 @@ impl InferenceType {
 
    /// Generates a new InferenceType. The two boolean flags will be checked in
 
    /// debug mode.
 
    fn new(has_body_marker: bool, is_done: bool, parts: Vec<InferenceTypePart>) -> Self {
 
        if cfg!(debug_assertions) {
 
            debug_assert!(!parts.is_empty());
 
            let parts_body_marker = parts.iter().any(|v| {
 
                if let InferenceTypePart::MarkerBody(_) = v { true } else { false }
 
            });
 
            debug_assert_eq!(has_body_marker, parts_body_marker);
 
            let parts_done = parts.iter().all(|v| v.is_concrete());
 
            debug_assert_eq!(is_done, parts_done, "{:?}", parts);
 
        }
 
        Self{ has_body_marker: has_body_marker, is_done, parts }
 
        Self{ has_body_marker, is_done, parts }
 
    }
 

	
 
    /// Replaces a type subtree with the provided subtree. The caller must make
 
    /// sure the the replacement is a well formed type subtree.
 
    fn replace_subtree(&mut self, start_idx: usize, with: &[InferenceTypePart]) {
 
        let end_idx = Self::find_subtree_end_idx(&self.parts, start_idx);
 
        debug_assert_eq!(with.len(), Self::find_subtree_end_idx(with, 0));
 
        self.parts.splice(start_idx..end_idx, with.iter().cloned());
 
        self.recompute_is_done();
 
    }
 

	
 
    // TODO: @performance, might all be done inline in the type inference methods
 
@@ -695,25 +702,25 @@ impl InferenceType {
 
            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));
 
                buffer.push_str(definition.identifier().value.as_str());
 
                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('>');
 
                }
 
            },
 
        }
 

	
 
@@ -751,25 +758,25 @@ 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::MarkerBody(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]))
 
                return Some((marker, &self.parts[start_idx..end_idx]));
 
            }
 

	
 
            self.idx += 1;
 
        }
 

	
 
        None
 
    }
 
}
 

	
 
#[derive(Debug, PartialEq, Eq)]
 
enum DualInferenceResult {
 
    Neither,        // neither argument is clarified
 
@@ -793,27 +800,35 @@ impl DualInferenceResult {
 
        }
 
    }
 
}
 

	
 
#[derive(Debug, PartialEq, Eq)]
 
enum SingleInferenceResult {
 
    Unmodified,
 
    Modified,
 
    Incompatible
 
}
 

	
 
enum DefinitionType{
 
    None, // Token value, never used during actual inference
 
    Component(ComponentId),
 
    Function(FunctionId),
 
    Component(ComponentDefinitionId),
 
    Function(FunctionDefinitionId),
 
}
 

	
 
impl DefinitionType {
 
    fn definition_id(&self) -> DefinitionId {
 
        match self {
 
            DefinitionType::Component(v) => v.upcast(),
 
            DefinitionType::Function(v) => v.upcast(),
 
        }
 
    }
 
}
 

	
 
#[derive(PartialEq, Eq)]
 
pub(crate) struct ResolveQueueElement {
 
    pub(crate) root_id: RootId,
 
    pub(crate) definition_id: DefinitionId,
 
    pub(crate) monomorph_types: Vec<ConcreteType>,
 
}
 

	
 
pub(crate) type ResolveQueue = Vec<ResolveQueueElement>;
 

	
 
/// This particular visitor will recurse depth-first into the AST and ensures
 
@@ -931,156 +946,151 @@ impl TypeResolvingVisitor {
 
        self.stmt_buffer.clear();
 
        self.expr_buffer.clear();
 
        self.var_types.clear();
 
        self.expr_types.clear();
 
        self.extra_data.clear();
 
        self.expr_queued.clear();
 
    }
 
}
 

	
 
impl Visitor2 for TypeResolvingVisitor {
 
    // Definitions
 

	
 
    fn visit_component_definition(&mut self, ctx: &mut Ctx, id: ComponentId) -> VisitorResult {
 
    fn visit_component_definition(&mut self, ctx: &mut Ctx, id: ComponentDefinitionId) -> VisitorResult {
 
        self.definition_type = DefinitionType::Component(id);
 

	
 
        let comp_def = &ctx.heap[id];
 
        debug_assert_eq!(comp_def.poly_vars.len(), self.poly_vars.len(), "component polyvars do not match imposed polyvars");
 

	
 
        debug_log!("{}", "-".repeat(50));
 
        debug_log!("Visiting component '{}': {}", &String::from_utf8_lossy(&comp_def.identifier.value), id.0.index);
 
        debug_log!("{}", "-".repeat(50));
 

	
 
        for param_id in comp_def.parameters.clone() {
 
            let param = &ctx.heap[param_id];
 
            let var_type = self.determine_inference_type_from_parser_type(ctx, param.parser_type, true);
 
            let var_type = self.determine_inference_type_from_parser_type(ctx, &param.parser_type, true);
 
            debug_assert!(var_type.is_done, "expected component arguments to be concrete types");
 
            self.var_types.insert(param_id.upcast(), VarData::new_local(var_type));
 
        }
 

	
 
        let body_stmt_id = ctx.heap[id].body;
 
        self.visit_stmt(ctx, body_stmt_id)
 
        self.visit_block_stmt(ctx, body_stmt_id)
 
    }
 

	
 
    fn visit_function_definition(&mut self, ctx: &mut Ctx, id: FunctionId) -> VisitorResult {
 
    fn visit_function_definition(&mut self, ctx: &mut Ctx, id: FunctionDefinitionId) -> VisitorResult {
 
        self.definition_type = DefinitionType::Function(id);
 

	
 
        let func_def = &ctx.heap[id];
 
        debug_assert_eq!(func_def.poly_vars.len(), self.poly_vars.len(), "function polyvars do not match imposed polyvars");
 

	
 
        debug_log!("{}", "-".repeat(50));
 
        debug_log!("Visiting function '{}': {}", &String::from_utf8_lossy(&func_def.identifier.value), id.0.index);
 
        debug_log!("{}", "-".repeat(50));
 

	
 
        for param_id in func_def.parameters.clone() {
 
            let param = &ctx.heap[param_id];
 
            let var_type = self.determine_inference_type_from_parser_type(ctx, param.parser_type, true);
 
            let var_type = self.determine_inference_type_from_parser_type(ctx, &param.parser_type, true);
 
            debug_assert!(var_type.is_done, "expected function arguments to be concrete types");
 
            self.var_types.insert(param_id.upcast(), VarData::new_local(var_type));
 
        }
 

	
 
        let body_stmt_id = ctx.heap[id].body;
 
        self.visit_stmt(ctx, body_stmt_id)
 
        self.visit_block_stmt(ctx, body_stmt_id)
 
    }
 

	
 
    // Statements
 

	
 
    fn visit_block_stmt(&mut self, ctx: &mut Ctx, id: BlockStatementId) -> VisitorResult {
 
        // Transfer statements for traversal
 
        let block = &ctx.heap[id];
 

	
 
        for stmt_id in block.statements.clone() {
 
            self.visit_stmt(ctx, stmt_id)?;
 
        }
 

	
 
        Ok(())
 
    }
 

	
 
    fn visit_local_memory_stmt(&mut self, ctx: &mut Ctx, id: MemoryStatementId) -> VisitorResult {
 
        let memory_stmt = &ctx.heap[id];
 

	
 
        let local = &ctx.heap[memory_stmt.variable];
 
        let var_type = self.determine_inference_type_from_parser_type(ctx, local.parser_type, true);
 
        let var_type = self.determine_inference_type_from_parser_type(ctx, &local.parser_type, true);
 
        self.var_types.insert(memory_stmt.variable.upcast(), VarData::new_local(var_type));
 

	
 
        Ok(())
 
    }
 

	
 
    fn visit_local_channel_stmt(&mut self, ctx: &mut Ctx, id: ChannelStatementId) -> VisitorResult {
 
        let channel_stmt = &ctx.heap[id];
 

	
 
        let from_local = &ctx.heap[channel_stmt.from];
 
        let from_var_type = self.determine_inference_type_from_parser_type(ctx, from_local.parser_type, true);
 
        let from_var_type = self.determine_inference_type_from_parser_type(ctx, &from_local.parser_type, true);
 
        self.var_types.insert(from_local.this.upcast(), VarData::new_channel(from_var_type, channel_stmt.to.upcast()));
 

	
 
        let to_local = &ctx.heap[channel_stmt.to];
 
        let to_var_type = self.determine_inference_type_from_parser_type(ctx, to_local.parser_type, true);
 
        let to_var_type = self.determine_inference_type_from_parser_type(ctx, &to_local.parser_type, true);
 
        self.var_types.insert(to_local.this.upcast(), VarData::new_channel(to_var_type, channel_stmt.from.upcast()));
 

	
 
        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];
 

	
 
        let true_body_id = if_stmt.true_body;
 
        let false_body_id = if_stmt.false_body;
 
        let test_expr_id = if_stmt.test;
 

	
 
        self.visit_expr(ctx, test_expr_id)?;
 
        self.visit_stmt(ctx, true_body_id)?;
 
        self.visit_stmt(ctx, false_body_id)?;
 
        self.visit_block_stmt(ctx, true_body_id)?;
 
        if let Some(false_body_id) = false_body_id {
 
            self.visit_block_stmt(ctx, false_body_id)?;
 
        }
 

	
 
        Ok(())
 
    }
 

	
 
    fn visit_while_stmt(&mut self, ctx: &mut Ctx, id: WhileStatementId) -> VisitorResult {
 
        let while_stmt = &ctx.heap[id];
 

	
 
        let body_id = while_stmt.body;
 
        let test_expr_id = while_stmt.test;
 

	
 
        self.visit_expr(ctx, test_expr_id)?;
 
        self.visit_stmt(ctx, body_id)?;
 
        self.visit_block_stmt(ctx, body_id)?;
 

	
 
        Ok(())
 
    }
 

	
 
    fn visit_synchronous_stmt(&mut self, ctx: &mut Ctx, id: SynchronousStatementId) -> VisitorResult {
 
        let sync_stmt = &ctx.heap[id];
 
        let body_id = sync_stmt.body;
 

	
 
        self.visit_stmt(ctx, body_id)
 
        self.visit_block_stmt(ctx, body_id)
 
    }
 

	
 
    fn visit_return_stmt(&mut self, ctx: &mut Ctx, id: ReturnStatementId) -> VisitorResult {
 
        let return_stmt = &ctx.heap[id];
 
        let expr_id = return_stmt.expression;
 

	
 
        self.visit_expr(ctx, expr_id)
 
    }
 

	
 
    fn visit_assert_stmt(&mut self, ctx: &mut Ctx, id: AssertStatementId) -> VisitorResult {
 
        let assert_stmt = &ctx.heap[id];
 
        let test_expr_id = assert_stmt.expression;
 

	
 
        self.visit_expr(ctx, test_expr_id)
 
    }
 

	
 
    fn visit_new_stmt(&mut self, ctx: &mut Ctx, id: NewStatementId) -> VisitorResult {
 
        let new_stmt = &ctx.heap[id];
 
        let call_expr_id = new_stmt.expression;
 

	
 
        self.visit_call_expr(ctx, call_expr_id)
 
    }
 

	
 
    fn visit_expr_stmt(&mut self, ctx: &mut Ctx, id: ExpressionStatementId) -> VisitorResult {
 
        let expr_stmt = &ctx.heap[id];
 
        let subexpr_id = expr_stmt.expression;
 

	
 
        self.visit_expr(ctx, subexpr_id)
 
@@ -1178,45 +1188,32 @@ impl Visitor2 for TypeResolvingVisitor {
 
    fn visit_select_expr(&mut self, ctx: &mut Ctx, id: SelectExpressionId) -> VisitorResult {
 
        let upcast_id = id.upcast();
 
        self.insert_initial_expr_inference_type(ctx, upcast_id)?;
 

	
 
        let select_expr = &ctx.heap[id];
 
        let subject_expr_id = select_expr.subject;
 

	
 
        self.visit_expr(ctx, subject_expr_id)?;
 

	
 
        self.progress_select_expr(ctx, id)
 
    }
 

	
 
    fn visit_array_expr(&mut self, ctx: &mut Ctx, id: ArrayExpressionId) -> VisitorResult {
 
        let upcast_id = id.upcast();
 
        self.insert_initial_expr_inference_type(ctx, upcast_id)?;
 

	
 
        let array_expr = &ctx.heap[id];
 
        // TODO: @performance
 
        for element_id in array_expr.elements.clone().into_iter() {
 
            self.visit_expr(ctx, element_id)?;
 
        }
 

	
 
        self.progress_array_expr(ctx, id)
 
    }
 

	
 
    fn visit_literal_expr(&mut self, ctx: &mut Ctx, id: LiteralExpressionId) -> VisitorResult {
 
        let upcast_id = id.upcast();
 
        self.insert_initial_expr_inference_type(ctx, upcast_id)?;
 

	
 
        let literal_expr = &ctx.heap[id];
 
        match &literal_expr.value {
 
            Literal::Null | Literal::False | Literal::True |
 
            Literal::Integer(_) | Literal::Character(_) => {
 
            Literal::Integer(_) | Literal::Character(_) | Literal::String(_) => {
 
                // No subexpressions
 
            },
 
            Literal::Struct(literal) => {
 
                // TODO: @performance
 
                let expr_ids: Vec<_> = literal.fields
 
                    .iter()
 
                    .map(|f| f.value)
 
                    .collect();
 

	
 
                self.insert_initial_struct_polymorph_data(ctx, id);
 

	
 
                for expr_id in expr_ids {
 
@@ -1227,24 +1224,31 @@ impl Visitor2 for TypeResolvingVisitor {
 
                // Enumerations do not carry any subexpressions, but may still
 
                // have a user-defined polymorphic marker variable. For this 
 
                // reason we may still have to apply inference to this 
 
                // polymorphic variable
 
                self.insert_initial_enum_polymorph_data(ctx, id);
 
            },
 
            Literal::Union(literal) => {
 
                // May carry subexpressions and polymorphic arguments
 
                // TODO: @performance
 
                let expr_ids = literal.values.clone();
 
                self.insert_initial_union_polymorph_data(ctx, id);
 

	
 
                for expr_id in expr_ids {
 
                    self.visit_expr(ctx, expr_id)?;
 
                }
 
            },
 
            Literal::Array(expressions) => {
 
                // TODO: @performance
 
                let expr_ids = expressions.clone();
 
                for expr_id in expr_ids {
 
                    self.visit_expr(ctx, expr_id)?;
 
                }
 
            }
 
        }
 

	
 
        self.progress_literal_expr(ctx, id)
 
    }
 

	
 
    fn visit_call_expr(&mut self, ctx: &mut Ctx, id: CallExpressionId) -> VisitorResult {
 
        let upcast_id = id.upcast();
 
        self.insert_initial_expr_inference_type(ctx, upcast_id)?;
 
@@ -1324,31 +1328,30 @@ impl TypeResolvingVisitor {
 
            DefinitionType::Function(id) => id.upcast(),
 
            _ => unreachable!(),
 
        };
 

	
 
        let already_checked = ctx.types.get_base_definition(&definition_id).unwrap().has_any_monomorph();
 
        for (expr_id, expr_type) in self.expr_types.iter_mut() {
 
            if !expr_type.is_done {
 
                // Auto-infer numberlike/integerlike types to a regular int
 
                if expr_type.parts.len() == 1 && expr_type.parts[0] == InferenceTypePart::IntegerLike {
 
                    expr_type.parts[0] = InferenceTypePart::Int;
 
                } else {
 
                    let expr = &ctx.heap[*expr_id];
 
                    return Err(ParseError::new_error(
 
                        &ctx.module.source, expr.position(),
 
                        &format!(
 
                            "Could not fully infer the type of this expression (got '{}')",
 
                    return Err(ParseError::new_error_at_span(
 
                        &ctx.module.source, expr.span(), format!(
 
                            "could not fully infer the type of this expression (got '{}')",
 
                            expr_type.display_name(&ctx.heap)
 
                        )
 
                    ))
 
                    ));
 
                }
 
            }
 

	
 
            if !already_checked {
 
                let concrete_type = ctx.heap[*expr_id].get_type_mut();
 
                expr_type.write_concrete_type(concrete_type);
 
            } else {
 
                if cfg!(debug_assertions) {
 
                    let mut concrete_type = ConcreteType::default();
 
                    expr_type.write_concrete_type(&mut concrete_type);
 
                    debug_assert_eq!(*ctx.heap[*expr_id].get_type(), concrete_type);
 
                }
 
@@ -1372,28 +1375,27 @@ impl TypeResolvingVisitor {
 
                Expression::Call(_) => true,
 
                Expression::Literal(_) => true,
 
                _ => false
 
            };
 

	
 
            if needs_full_inference {
 
                let mut monomorph_types = Vec::with_capacity(extra_data.poly_vars.len());
 
                for (poly_idx, poly_type) in extra_data.poly_vars.iter().enumerate() {
 
                    if !poly_type.is_done {
 
                        // TODO: Single clean function for function signatures and polyvars.
 
                        // TODO: Better error message
 
                        let expr = &ctx.heap[*expr_id];
 
                        return Err(ParseError::new_error(
 
                            &ctx.module.source, expr.position(),
 
                            &format!(
 
                                "Could not fully infer the type of polymorphic variable {} of this expression (got '{}')",
 
                        return Err(ParseError::new_error_at_span(
 
                            &ctx.module.source, expr.span(), format!(
 
                                "could not fully infer the type of polymorphic variable {} of this expression (got '{}')",
 
                                poly_idx, poly_type.display_name(&ctx.heap)
 
                            )
 
                        ))
 
                    }
 

	
 
                    let mut concrete_type = ConcreteType::default();
 
                    poly_type.write_concrete_type(&mut concrete_type);
 
                    monomorph_types.insert(poly_idx, concrete_type);
 
                }
 

	
 
                // Resolve to the appropriate expression and instantiate 
 
                // monomorphs.
 
@@ -1465,28 +1467,24 @@ impl TypeResolvingVisitor {
 
            Expression::Indexing(expr) => {
 
                let id = expr.this;
 
                self.progress_indexing_expr(ctx, id)
 
            },
 
            Expression::Slicing(expr) => {
 
                let id = expr.this;
 
                self.progress_slicing_expr(ctx, id)
 
            },
 
            Expression::Select(expr) => {
 
                let id = expr.this;
 
                self.progress_select_expr(ctx, id)
 
            },
 
            Expression::Array(expr) => {
 
                let id = expr.this;
 
                self.progress_array_expr(ctx, id)
 
            },
 
            Expression::Literal(expr) => {
 
                let id = expr.this;
 
                self.progress_literal_expr(ctx, id)
 
            },
 
            Expression::Call(expr) => {
 
                let id = expr.this;
 
                self.progress_call_expr(ctx, id)
 
            },
 
            Expression::Variable(expr) => {
 
                let id = expr.this;
 
                self.progress_variable_expr(ctx, id)
 
            }
 
@@ -1814,67 +1812,64 @@ impl TypeResolvingVisitor {
 
                if field.definition.is_none() {
 
                    // Not yet known, check if we can determine it
 
                    let subject_type = self.expr_types.get(&subject_id).unwrap();
 
                    let type_def = determine_inference_type_instance(&ctx.types, subject_type);
 

	
 
                    match type_def {
 
                        Ok(Some(type_def)) => {
 
                            // Subject type is known, check if it is a 
 
                            // struct and the field exists on the struct
 
                            let struct_def = if let DefinedTypeVariant::Struct(struct_def) = &type_def.definition {
 
                                struct_def
 
                            } else {
 
                                return Err(ParseError::new_error(
 
                                    &ctx.module.source, field.identifier.position,
 
                                    &format!(
 
                                return Err(ParseError::new_error_at_span(
 
                                    &ctx.module.source, field.identifier.span, format!(
 
                                        "Can only apply field access to structs, got a subject of type '{}'",
 
                                        subject_type.display_name(&ctx.heap)
 
                                    )
 
                                ));
 
                            };
 

	
 
                            for (field_def_idx, field_def) in struct_def.fields.iter().enumerate() {
 
                                if field_def.identifier == field.identifier {
 
                                    // Set field definition and index
 
                                    field.definition = Some(type_def.ast_definition);
 
                                    field.field_idx = field_def_idx;
 
                                    break;
 
                                }
 
                            }
 

	
 
                            if field.definition.is_none() {
 
                                let field_position = field.identifier.position;
 
                                let field_span = field.identifier.span;
 
                                let ast_struct_def = ctx.heap[type_def.ast_definition].as_struct();
 
                                return Err(ParseError::new_error(
 
                                    &ctx.module.source, field_position,
 
                                    &format!(
 
                                        "This field does not exist on the struct '{}'",
 
                                        &String::from_utf8_lossy(&ast_struct_def.identifier.value)
 
                                return Err(ParseError::new_error_at_span(
 
                                    &ctx.module.source, field_span, format!(
 
                                        "this field does not exist on the struct '{}'",
 
                                        ast_struct_def.identifier.value.as_str()
 
                                    )
 
                                ))
 
                            }
 

	
 
                            // Encountered definition and field index for the
 
                            // first time
 
                            self.insert_initial_select_polymorph_data(ctx, id);
 
                        },
 
                        Ok(None) => {
 
                            // Type of subject is not yet known, so we 
 
                            // cannot make any progress yet
 
                            return Ok(())
 
                        },
 
                        Err(()) => {
 
                            return Err(ParseError::new_error(
 
                                &ctx.module.source, field.identifier.position,
 
                                &format!(
 
                            return Err(ParseError::new_error_at_span(
 
                                &ctx.module.source, field.identifier.span, format!(
 
                                    "Can only apply field access to structs, got a subject of type '{}'",
 
                                    subject_type.display_name(&ctx.heap)
 
                                )
 
                            ));
 
                        }
 
                    }
 
                }
 

	
 
                // If here then field definition and index are known, and the
 
                // initial type (based on the struct's definition) has been
 
                // applied.
 
                // Check to see if we can infer anything about the subject's and
 
@@ -1930,84 +1925,50 @@ impl TypeResolvingVisitor {
 
        };
 

	
 
        if progress_subject { self.queue_expr(subject_id); }
 
        if progress_expr { self.queue_expr_parent(ctx, upcast_id); }
 

	
 
        debug_log!(" * After:");
 
        debug_log!("   - Subject type [{}]: {}", progress_subject, self.expr_types.get(&subject_id).unwrap().display_name(&ctx.heap));
 
        debug_log!("   - Expr    type [{}]: {}", progress_expr, self.expr_types.get(&upcast_id).unwrap().display_name(&ctx.heap));
 

	
 
        Ok(())
 
    }
 

	
 
    fn progress_array_expr(&mut self, ctx: &mut Ctx, id: ArrayExpressionId) -> Result<(), ParseError> {
 
        let upcast_id = id.upcast();
 
        let expr = &ctx.heap[id];
 
        let expr_elements = expr.elements.clone(); // TODO: @performance
 

	
 
        debug_log!("Array expr ({} elements): {}", expr_elements.len(), upcast_id.index);
 
        debug_log!(" * Before:");
 
        debug_log!("   - Expr type: {}", self.expr_types.get(&upcast_id).unwrap().display_name(&ctx.heap));
 

	
 
        // All elements should have an equal type
 
        let progress = self.apply_equal_n_constraint(ctx, upcast_id, &expr_elements)?;
 
        for (progress_arg, arg_id) in progress.iter().zip(expr_elements.iter()) {
 
            if *progress_arg {
 
                self.queue_expr(*arg_id);
 
            }
 
        }
 

	
 
        // And the output should be an array of the element types
 
        let mut expr_progress = self.apply_forced_constraint(ctx, upcast_id, &ARRAY_TEMPLATE)?;
 
        if !expr_elements.is_empty() {
 
            let first_arg_id = expr_elements[0];
 
            let (inner_expr_progress, arg_progress) = self.apply_equal2_constraint(
 
                ctx, upcast_id, upcast_id, 1, first_arg_id, 0
 
            )?;
 

	
 
            expr_progress = expr_progress || inner_expr_progress;
 

	
 
            // Note that if the array type progressed the type of the arguments,
 
            // then we should enqueue this progression function again
 
            // TODO: @fix Make apply_equal_n accept a start idx as well
 
            if arg_progress { self.queue_expr(upcast_id); }
 
        }
 

	
 
        debug_log!(" * After:");
 
        debug_log!("   - Expr type [{}]: {}", expr_progress, self.expr_types.get(&upcast_id).unwrap().display_name(&ctx.heap));
 

	
 
        if expr_progress { self.queue_expr_parent(ctx, upcast_id); }
 

	
 
        Ok(())
 
    }
 

	
 
    fn progress_literal_expr(&mut self, ctx: &mut Ctx, id: LiteralExpressionId) -> Result<(), ParseError> {
 
        let upcast_id = id.upcast();
 
        let expr = &ctx.heap[id];
 

	
 
        debug_log!("Literal expr: {}", upcast_id.index);
 
        debug_log!(" * Before:");
 
        debug_log!("   - Expr type: {}", self.expr_types.get(&upcast_id).unwrap().display_name(&ctx.heap));
 

	
 
        let progress_expr = match &expr.value {
 
            Literal::Null => {
 
                self.apply_forced_constraint(ctx, upcast_id, &MESSAGE_TEMPLATE)?
 
            },
 
            Literal::Integer(_) => {
 
                self.apply_forced_constraint(ctx, upcast_id, &INTEGERLIKE_TEMPLATE)?
 
            },
 
            Literal::True | Literal::False => {
 
                self.apply_forced_constraint(ctx, upcast_id, &BOOL_TEMPLATE)?
 
            },
 
            Literal::Character(_) => todo!("character literals"),
 
            Literal::Character(_) => {
 
                todo!("check character literal type inference");
 
                self.apply_forced_constraint(ctx, upcast_id, &CHARACTER_TEMPLATE)?
 
            },
 
            Literal::String(_) => {
 
                todo!("check string literal type inference");
 
                self.apply_forced_constraint(ctx, upcast_id, &STRING_TEMPLATE)?
 
            },
 
            Literal::Struct(data) => {
 
                let extra = self.extra_data.get_mut(&upcast_id).unwrap();
 
                for poly in &extra.poly_vars {
 
                    debug_log!(" * Poly: {}", poly.display_name(&ctx.heap));
 
                }
 
                let mut poly_progress = HashSet::new();
 
                debug_assert_eq!(extra.embedded.len(), data.fields.len());
 

	
 
                debug_log!(" * During (inferring types from fields and struct type):");
 

	
 
                // Mutually infer field signature/expression types
 
                for (field_idx, field) in data.fields.iter().enumerate() {
 
@@ -2203,25 +2164,60 @@ impl TypeResolvingVisitor {
 
                    }
 
                }
 

	
 
                // And for the union type itself
 
                let signature_type: *mut _ = &mut extra.returned;
 
                let expr_type: *mut _ = self.expr_types.get_mut(&upcast_id).unwrap();
 

	
 
                let progress_expr = Self::apply_equal2_polyvar_constraint(
 
                    &ctx.heap, extra, &poly_progress, signature_type, expr_type
 
                );
 

	
 
                progress_expr
 
            }
 
            },
 
            Literal::Array(data) => {
 
                let expr_elements = data.clone(); // TODO: @performance
 
                debug_log!("Array expr ({} elements): {}", expr_elements.len(), upcast_id.index);
 
                debug_log!(" * Before:");
 
                debug_log!("   - Expr type: {}", self.expr_types.get(&upcast_id).unwrap().display_name(&ctx.heap));
 

	
 
                // All elements should have an equal type
 
                let progress = self.apply_equal_n_constraint(ctx, upcast_id, &expr_elements)?;
 
                for (progress_arg, arg_id) in progress.iter().zip(expr_elements.iter()) {
 
                    if *progress_arg {
 
                        self.queue_expr(*arg_id);
 
                    }
 
                }
 

	
 
                // And the output should be an array of the element types
 
                let mut progress_expr = self.apply_forced_constraint(ctx, upcast_id, &ARRAY_TEMPLATE)?;
 
                if !expr_elements.is_empty() {
 
                    let first_arg_id = expr_elements[0];
 
                    let (inner_expr_progress, arg_progress) = self.apply_equal2_constraint(
 
                        ctx, upcast_id, upcast_id, 1, first_arg_id, 0
 
                    )?;
 

	
 
                    progress_expr = progress_expr || inner_expr_progress;
 

	
 
                    // Note that if the array type progressed the type of the arguments,
 
                    // then we should enqueue this progression function again
 
                    // TODO: @fix Make apply_equal_n accept a start idx as well
 
                    if arg_progress { self.queue_expr(upcast_id); }
 
                }
 

	
 
                debug_log!(" * After:");
 
                debug_log!("   - Expr type [{}]: {}", progress_expr, self.expr_types.get(&upcast_id).unwrap().display_name(&ctx.heap));
 

	
 
                progress_expr
 
            },
 
        };
 

	
 
        debug_log!(" * After:");
 
        debug_log!("   - Expr type: {}", self.expr_types.get(&upcast_id).unwrap().display_name(&ctx.heap));
 

	
 
        // TODO: FIX!!!!
 
        if progress_expr { self.queue_expr_parent(ctx, upcast_id); }
 

	
 
        Ok(())
 
    }
 

	
 
    // TODO: @cleanup, see how this can be cleaned up once I implement
 
@@ -2350,33 +2346,31 @@ impl TypeResolvingVisitor {
 
        debug_log!("   - Var  type: {}", self.var_types.get(&var_id).unwrap().var_type.display_name(&ctx.heap));
 
        debug_log!("   - Expr type: {}", self.expr_types.get(&upcast_id).unwrap().display_name(&ctx.heap));
 

	
 
        // Retrieve shared variable type and expression type and apply inference
 
        let var_data = self.var_types.get_mut(&var_id).unwrap();
 
        let expr_type = self.expr_types.get_mut(&upcast_id).unwrap();
 

	
 
        let infer_res = unsafe{ InferenceType::infer_subtrees_for_both_types(
 
            &mut var_data.var_type as *mut _, 0, expr_type, 0
 
        ) };
 
        if infer_res == DualInferenceResult::Incompatible {
 
            let var_decl = &ctx.heap[var_id];
 
            return Err(ParseError::new_error(
 
                &ctx.module.source, var_decl.position(),
 
                &format!(
 
            return Err(ParseError::new_error_at_span(
 
                &ctx.module.source, var_decl.identifier().span, format!(
 
                    "Conflicting types for this variable, previously assigned the type '{}'",
 
                    var_data.var_type.display_name(&ctx.heap)
 
                )
 
            ).with_postfixed_info(
 
                &ctx.module.source, var_expr.position,
 
                &format!(
 
            ).with_info_at_span(
 
                &ctx.module.source, var_expr.identifier.span, format!(
 
                    "But inferred to have incompatible type '{}' here",
 
                    expr_type.display_name(&ctx.heap)
 
                )
 
            ))
 
        }
 

	
 
        let progress_var = infer_res.modified_lhs();
 
        let progress_expr = infer_res.modified_rhs();
 

	
 
        if progress_var {
 
            // Let other variable expressions using this type progress as well
 
            for other_expr in var_data.used_at.iter() {
 
@@ -2404,33 +2398,31 @@ impl TypeResolvingVisitor {
 
                    SingleInferenceResult::Modified => {
 
                        for other_expr in &link_data.used_at {
 
                            self.expr_queued.insert(*other_expr);
 
                        }
 
                    },
 
                    SingleInferenceResult::Unmodified => {},
 
                    SingleInferenceResult::Incompatible => {
 
                        let var_data = self.var_types.get(&var_id).unwrap();
 
                        let link_data = self.var_types.get(&linked_id).unwrap();
 
                        let var_decl = &ctx.heap[var_id];
 
                        let link_decl = &ctx.heap[linked_id];
 

	
 
                        return Err(ParseError::new_error(
 
                            &ctx.module.source, var_decl.position(),
 
                            &format!(
 
                        return Err(ParseError::new_error_at_span(
 
                            &ctx.module.source, var_decl.identifier().span, format!(
 
                                "Conflicting types for this variable, assigned the type '{}'",
 
                                var_data.var_type.display_name(&ctx.heap)
 
                            )
 
                        ).with_postfixed_info(
 
                            &ctx.module.source, link_decl.position(),
 
                            &format!(
 
                        ).with_info_at_span(
 
                            &ctx.module.source, link_decl.identifier().span, format!(
 
                                "Because it is incompatible with this variable, assigned the type '{}'",
 
                                link_data.var_type.display_name(&ctx.heap)
 
                            )
 
                        ));
 
                    }
 
                }
 
            }
 
        }
 
        if progress_expr { self.queue_expr_parent(ctx, upcast_id); }
 

	
 
        debug_log!(" * After:");
 
        debug_log!("   - Var  type [{}]: {}", progress_var, self.var_types.get(&var_id).unwrap().var_type.display_name(&ctx.heap));
 
@@ -2526,42 +2518,41 @@ impl TypeResolvingVisitor {
 
        debug_assert_ptrs_distinct!(signature_type, expression_type);
 

	
 
        // Infer the signature and expression type
 
        let infer_res = unsafe { 
 
            InferenceType::infer_subtrees_for_both_types(
 
                signature_type, signature_start_idx,
 
                expression_type, expression_start_idx
 
            ) 
 
        };
 

	
 
        if infer_res == DualInferenceResult::Incompatible {
 
            // TODO: Check if I still need to use this
 
            let outer_position = ctx.heap[outer_expr_id].position();
 
            let (position_name, position) = match expr_id {
 
                Some(expr_id) => ("argument's", ctx.heap[expr_id].position()),
 
                None => ("type's", outer_position)
 
            let outer_span = ctx.heap[outer_expr_id].span();
 
            let (span_name, span) = match expr_id {
 
                Some(expr_id) => ("argument's", ctx.heap[expr_id].span()),
 
                None => ("type's", outer_span)
 
            };
 
            let (signature_display_type, expression_display_type) = unsafe { (
 
                (&*signature_type).display_name(&ctx.heap),
 
                (&*expression_type).display_name(&ctx.heap)
 
            ) };
 

	
 
            return Err(ParseError::new_error(
 
                &ctx.module.source, outer_position,
 
                "Failed to fully resolve the types of this expression"
 
            ).with_postfixed_info(
 
                &ctx.module.source, position,
 
                &format!(
 
                    "Because the {} signature has been resolved to '{}', but the expression has been resolved to '{}'",
 
                    position_name, signature_display_type, expression_display_type
 
            return Err(ParseError::new_error_str_at_span(
 
                &ctx.module.source, outer_span,
 
                "failed to fully resolve the types of this expression"
 
            ).with_info_at_span(
 
                &ctx.module.source, span, format!(
 
                    "because the {} signature has been resolved to '{}', but the expression has been resolved to '{}'",
 
                    span_name, signature_display_type, expression_display_type
 
                )
 
            ));
 
        }
 

	
 
        // Try to see if we can progress any of the polymorphic variables
 
        let progress_sig = infer_res.modified_lhs();
 
        let progress_expr = infer_res.modified_rhs();
 

	
 
        if progress_sig {
 
            let signature_type = unsafe{&mut *signature_type};
 
            debug_assert!(
 
                signature_type.has_body_marker, 
 
@@ -2864,40 +2855,40 @@ impl TypeResolvingVisitor {
 
                    InferenceType::new(false, true, vec![ITP::Void])
 
                )
 
            }
 
            Method::Symbolic(symbolic) => {
 
                let definition = &ctx.heap[symbolic.definition.unwrap()];
 

	
 
                match definition {
 
                    Definition::Component(definition) => {
 
                        debug_assert_eq!(poly_vars.len(), definition.poly_vars.len());
 
                        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.push(self.determine_inference_type_from_parser_type(ctx, &param.parser_type, false));
 
                        }
 

	
 
                        (parameter_types, InferenceType::new(false, true, vec![InferenceTypePart::Void]))
 
                    },
 
                    Definition::Function(definition) => {
 
                        debug_assert_eq!(poly_vars.len(), definition.poly_vars.len());
 
                        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.push(self.determine_inference_type_from_parser_type(ctx, &param.parser_type, false));
 
                        }
 

	
 
                        let return_type = self.determine_inference_type_from_parser_type(ctx, definition.return_type, false);
 
                        debug_assert_eq!(definition.return_types.len(), 1, "multiple return types not yet implemented");
 

	
 
                        let return_type = self.determine_inference_type_from_parser_type(ctx, &definition.return_types[0], false);
 
                        (parameter_types, return_type)
 
                    },
 
                    Definition::Struct(_) | Definition::Enum(_) | Definition::Union(_) => {
 
                        unreachable!("insert initial polymorph data for struct/enum/union");
 
                    }
 
                }
 
            }
 
        };
 

	
 
        self.extra_data.insert(call_id.upcast(), ExtraData {
 
            poly_vars,
 
            embedded: embedded_types,
 
@@ -2930,25 +2921,25 @@ impl TypeResolvingVisitor {
 
                definition
 
            },
 
            _ => unreachable!("definition for struct literal does not point to struct definition")
 
        };
 

	
 
        // Note: programmer is capable of specifying fields in a struct literal
 
        // in a different order than on the definition. We take the literal-
 
        // specified order to be leading.
 
        let mut embedded_types = Vec::with_capacity(definition.fields.len());
 
        for lit_field in literal.fields.iter() {
 
            let def_field = &definition.fields[lit_field.field_idx];
 
            let inference_type = self.determine_inference_type_from_parser_type(
 
                ctx, def_field.parser_type, false
 
                ctx, &def_field.parser_type, false
 
            );
 
            embedded_types.push(inference_type);
 
        }
 

	
 
        // Return type is the struct type itself, with the appropriate 
 
        // polymorphic variables. So:
 
        // - 1 part for definition
 
        // - N_poly_arg marker parts for each polymorphic argument
 
        // - all the parts for the currently known polymorphic arguments 
 
        let parts_reserved = 1 + poly_vars.len() + total_num_poly_parts;
 
        let mut parts = Vec::with_capacity(parts_reserved);
 
        parts.push(ITP::Instance(definition.this.upcast(), poly_vars.len()));
 
@@ -3094,213 +3085,175 @@ impl TypeResolvingVisitor {
 

	
 
        for poly_idx in 0..num_poly_vars {
 
            poly_vars.push(InferenceType::new(true, false, vec![
 
                ITP::MarkerBody(poly_idx), ITP::Unknown,
 
            ]));
 
            struct_parts.push(ITP::MarkerBody(poly_idx));
 
            struct_parts.push(ITP::Unknown);
 
        }
 
        debug_assert_eq!(struct_parts.len(), struct_parts_reserved);
 

	
 
        // Generate initial field type
 
        let field_type = self.determine_inference_type_from_parser_type(
 
            ctx, definition.fields[field_idx].parser_type, false
 
            ctx, &definition.fields[field_idx].parser_type, false
 
        );
 

	
 
        self.extra_data.insert(select_id.upcast(), ExtraData{
 
            poly_vars,
 
            embedded: vec![InferenceType::new(num_poly_vars != 0, num_poly_vars == 0, struct_parts)],
 
            returned: field_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,
 
        &mut self, ctx: &Ctx, parser_type: &ParserType,
 
        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 infer_type = Vec::with_capacity(parser_type.elements.len());
 
        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 {
 
        for element in &parser_type.elements {
 
            match &element.variant {
 
                PTV::Message => {
 
                    // TODO: @types Remove the Message -> Byte hack at some point...
 
                    infer_type.push(ITP::Message);
 
                    infer_type.push(ITP::Byte);
 
                    infer_type.push(ITP::UInt8);
 
                },
 
                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::UInt8 => { infer_type.push(ITP::UInt8); },
 
                PTV::UInt16 => { infer_type.push(ITP::UInt16); },
 
                PTV::UInt32 => { infer_type.push(ITP::UInt32); },
 
                PTV::UInt64 => { infer_type.push(ITP::UInt64); },
 
                PTV::SInt8 => { infer_type.push(ITP::SInt8); },
 
                PTV::SInt16 => { infer_type.push(ITP::SInt16); },
 
                PTV::SInt32 => { infer_type.push(ITP::SInt32); },
 
                PTV::SInt64 => { infer_type.push(ITP::SInt64); },
 
                PTV::Character => { infer_type.push(ITP::Character); },
 
                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.as_ref().unwrap() {
 
                        SymbolicParserTypeVariant::PolyArg(_, arg_idx) => {
 
                            let arg_idx = *arg_idx;
 
                            debug_assert!(symbolic.poly_args2.is_empty()); // TODO: @hkt
 

	
 
                            if parser_type_in_body {
 
                                // Polymorphic argument refers to definition's
 
                                // polymorphic variables
 
                                debug_assert!(arg_idx < self.poly_vars.len());
 
                                debug_assert!(!self.poly_vars[arg_idx].has_marker());
 
                                infer_type.push(ITP::MarkerDefinition(arg_idx));
 
                                for concrete_part in &self.poly_vars[arg_idx].parts {
 
                                    infer_type.push(ITP::from(*concrete_part));
 
                                }
 
                            } else {
 
                                // Polymorphic argument has to be inferred
 
                                has_markers = true;
 
                                has_inferred = true;
 
                                infer_type.push(ITP::MarkerBody(arg_idx));
 
                                infer_type.push(ITP::Unknown);
 
                            }
 
                        },
 
                        SymbolicParserTypeVariant::Definition(definition_id) => {
 
                            // TODO: @cleanup
 
                            if cfg!(debug_assertions) {
 
                                let definition = &ctx.heap[*definition_id];
 
                                debug_assert!(definition.is_struct() || definition.is_enum() || definition.is_union()); // TODO: @function_ptrs
 
                                let num_poly = match definition {
 
                                    Definition::Struct(v) => v.poly_vars.len(),
 
                                    Definition::Enum(v) => v.poly_vars.len(),
 
                                    Definition::Union(v) => v.poly_vars.len(),
 
                                    _ => unreachable!(),
 
                                };
 
                                debug_assert_eq!(symbolic.poly_args2.len(), num_poly);
 
                            }
 

	
 
                            infer_type.push(ITP::Instance(*definition_id, symbolic.poly_args2.len()));
 
                            let mut poly_arg_idx = symbolic.poly_args2.len();
 
                            while poly_arg_idx > 0 {
 
                                poly_arg_idx -= 1;
 
                                to_consider.push_front(symbolic.poly_args2[poly_arg_idx]);
 
                            }
 
                PTV::Array => { infer_type.push(ITP::Array); },
 
                PTV::Input => { infer_type.push(ITP::Input); },
 
                PTV::Output => { infer_type.push(ITP::Output); },
 
                PTV::PolymorphicArgument(belongs_to_definition, poly_arg_idx) => {
 
                    let poly_arg_idx = *poly_arg_idx;
 
                    if parser_type_in_body {
 
                        // Refers to polymorphic argument on procedure we're currently processing.
 
                        // This argument is already known.
 
                        debug_assert_eq!(belongs_to_definition, self.definition_type.definition_id());
 
                        debug_assert!((poly_arg_idx as usize) < self.poly_vars.len());
 

	
 
                        infer_type.push(ITP::MarkerDefinition(poly_arg_idx as usize));
 
                        for concrete_part in &self.poly_vars[poly_arg_idx].parts {
 
                            infer_types.push(ITP::from(*concrete_part));
 
                        }
 
                    } else {
 
                        // Polymorphic argument has to be inferred
 
                        has_markers = true;
 
                        has_inferred = true;
 
                        infer_type.push(ITP::MarkerBody(poly_arg_idx));
 
                        infer_type.push(ITP::Unknown)
 
                    }
 
                },
 
                PTV::Definition(definition_id, num_embedded) => {
 
                    infer_type.push(ITP::Instance(*definition_id, *num_embedded));
 
                }
 
            }
 
        }
 

	
 
        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
 
    ) -> ParseError {
 
        // TODO: Expand and provide more meaningful information for humans
 
        let expr = &ctx.heap[expr_id];
 
        let arg_expr = &ctx.heap[arg_id];
 
        let expr_type = self.expr_types.get(&expr_id).unwrap();
 
        let arg_type = self.expr_types.get(&arg_id).unwrap();
 

	
 
        return ParseError::new_error(
 
            &ctx.module.source, expr.position(),
 
            &format!(
 
                "Incompatible types: this expression expected a '{}'", 
 
        return ParseError::new_error_at_span(
 
            &ctx.module.source, expr.span(), 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 '{}'",
 
            &ctx.module.source, arg_expr.span(), format!(
 
                "but this expression yields a '{}'",
 
                arg_type.display_name(&ctx.heap)
 
            )
 
        )
 
    }
 

	
 
    fn construct_arg_type_error(
 
        &self, ctx: &Ctx, expr_id: ExpressionId,
 
        arg1_id: ExpressionId, arg2_id: ExpressionId
 
    ) -> ParseError {
 
        let expr = &ctx.heap[expr_id];
 
        let arg1 = &ctx.heap[arg1_id];
 
        let arg2 = &ctx.heap[arg2_id];
 

	
 
        let arg1_type = self.expr_types.get(&arg1_id).unwrap();
 
        let arg2_type = self.expr_types.get(&arg2_id).unwrap();
 

	
 
        return ParseError::new_error(
 
            &ctx.module.source, expr.position(),
 
            "Incompatible types: cannot apply this expression"
 
        ).with_postfixed_info(
 
            &ctx.module.source, arg1.position(),
 
            &format!(
 
        return ParseError::new_error_str_at_span(
 
            &ctx.module.source, expr.span(),
 
            "incompatible types: cannot apply this expression"
 
        ).with_info_at_span(
 
            &ctx.module.source, arg1.span(), format!(
 
                "Because this expression has type '{}'",
 
                arg1_type.display_name(&ctx.heap)
 
            )
 
        ).with_postfixed_info(
 
            &ctx.module.source, arg2.position(),
 
            &format!(
 
        ).with_info_at_span(
 
            &ctx.module.source, arg2.span(), format!(
 
                "But this expression has type '{}'",
 
                arg2_type.display_name(&ctx.heap)
 
            )
 
        )
 
    }
 

	
 
    fn construct_template_type_error(
 
        &self, ctx: &Ctx, expr_id: ExpressionId, template: &[InferenceTypePart]
 
    ) -> ParseError {
 
        let expr = &ctx.heap[expr_id];
 
        let expr_type = self.expr_types.get(&expr_id).unwrap();
 

	
 
        return ParseError::new_error(
 
            &ctx.module.source, expr.position(),
 
            &format!(
 
                "Incompatible types: got a '{}' but expected a '{}'",
 
        return ParseError::new_error_at_span(
 
            &ctx.module.source, expr.span(), format!(
 
                "incompatible types: got a '{}' but expected a '{}'",
 
                expr_type.display_name(&ctx.heap), 
 
                InferenceType::partial_display_name(&ctx.heap, template)
 
            )
 
        )
 
    }
 

	
 
    /// Constructs a human interpretable error in the case that type inference
 
    /// on a polymorphic variable to a function call or literal construction 
 
    /// failed. This may only be caused by a pair of inference types (which may 
 
    /// come from arguments or the return type) having two different inferred 
 
    /// values for that polymorphic variable.
 
    ///
 
@@ -3543,27 +3496,27 @@ impl TypeResolvingVisitor {
 

	
 
#[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::Byte),
 
            (ITP::IntegerLike, ITP::Int),
 
            (ITP::Unknown, ITP::Long),
 
            (ITP::NumberLike, ITP::UInt8),
 
            (ITP::IntegerLike, ITP::SInt32),
 
            (ITP::Unknown, ITP::UInt64),
 
            (ITP::Unknown, ITP::String)
 
        ];
 
        for (lhs, rhs) in pairs.iter() {
 
            // Using infer-both
 
            let mut lhs_type = IT::new(false, false, vec![lhs.clone()]);
 
            let mut rhs_type = IT::new(false, true, vec![rhs.clone()]);
 
            let result = unsafe{ IT::infer_subtrees_for_both_types(
 
                &mut lhs_type, 0, &mut rhs_type, 0
 
            ) };
 
            assert_eq!(DualInferenceResult::First, result);
 
            assert_eq!(lhs_type.parts, rhs_type.parts);
 

	
 
@@ -3572,31 +3525,31 @@ mod tests {
 
            let rhs_type = IT::new(false, true, vec![rhs.clone()]);
 
            let result = IT::infer_subtree_for_single_type(
 
                &mut lhs_type, 0, &rhs_type.parts, 0
 
            );
 
            assert_eq!(SingleInferenceResult::Modified, result);
 
            assert_eq!(lhs_type.parts, rhs_type.parts);
 
        }
 
    }
 

	
 
    #[test]
 
    fn test_multi_part_inference() {
 
        let pairs = [
 
            (vec![ITP::ArrayLike, ITP::NumberLike], vec![ITP::Slice, ITP::Byte]),
 
            (vec![ITP::ArrayLike, ITP::NumberLike], vec![ITP::Slice, ITP::SInt8]),
 
            (vec![ITP::Unknown], vec![ITP::Input, ITP::Array, ITP::String]),
 
            (vec![ITP::PortLike, ITP::Int], vec![ITP::Input, ITP::Int]),
 
            (vec![ITP::Unknown], vec![ITP::Output, ITP::Int]),
 
            (vec![ITP::PortLike, ITP::SInt32], vec![ITP::Input, ITP::SInt32]),
 
            (vec![ITP::Unknown], vec![ITP::Output, ITP::SInt32]),
 
            (
 
                vec![ITP::Instance(Id::new(0), 2), ITP::Input, ITP::Unknown, ITP::Output, ITP::Unknown],
 
                vec![ITP::Instance(Id::new(0), 2), ITP::Input, ITP::Array, ITP::Int, ITP::Output, ITP::Int]
 
                vec![ITP::Instance(Id::new(0), 2), ITP::Input, ITP::Array, ITP::SInt32, ITP::Output, ITP::SInt32]
 
            )
 
        ];
 

	
 
        for (lhs, rhs) in pairs.iter() {
 
            let mut lhs_type = IT::new(false, false, lhs.clone());
 
            let mut rhs_type = IT::new(false, true, rhs.clone());
 
            let result = unsafe{ IT::infer_subtrees_for_both_types(
 
                &mut lhs_type, 0, &mut rhs_type, 0
 
            ) };
 
            assert_eq!(DualInferenceResult::First, result);
 
            assert_eq!(lhs_type.parts, rhs_type.parts);
 

	
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