Add typechecking

reid/examples/reid/fibonacci.reid

@@ -1,5 +1,5 @@
 // Main
-fn main() {
+fn main() -> i32 {
     return fibonacci(3);
 }
 

reid/examples/testcodegen.rs

@@ -7,6 +7,7 @@ fn main() {
 
     let fibonacci = FunctionDefinition {
         name: fibonacci_name.clone(),
+        return_type: TypeKind::I32,
         parameters: vec![(fibonacci_n.clone(), TypeKind::I32)],
         kind: FunctionDefinitionKind::Local(
             Block {
@@ -126,6 +127,7 @@ fn main() {
 
     let main = FunctionDefinition {
         name: "main".to_owned(),
+        return_type: TypeKind::I32,
         parameters: vec![],
         kind: FunctionDefinitionKind::Local(
             Block {

reid/src/ast/process.rs

@@ -12,56 +12,34 @@ pub enum InferredType {
     Static(mir::TypeKind),
     OneOf(Vec<InferredType>),
     Void,
+    Unknown,
 }
 
 impl InferredType {
-    fn collapse(&self, scope: &VirtualScope) -> mir::TypeKind {
+    fn collapse(&self) -> mir::TypeKind {
         match self {
-            InferredType::FromVariable(name) => {
-                if let Some(inferred) = scope.get_var(name) {
-                    inferred.collapse(scope)
-                } else {
-                    mir::TypeKind::Vague(mir::VagueType::Unknown)
-                }
-            }
-            InferredType::FunctionReturn(name) => {
-                if let Some(type_kind) = scope.get_return_type(name) {
-                    type_kind.clone()
-                } else {
-                    mir::TypeKind::Vague(mir::VagueType::Unknown)
-                }
-            }
+            InferredType::FromVariable(_) => mir::TypeKind::Vague(mir::VagueType::Unknown),
+            InferredType::FunctionReturn(_) => mir::TypeKind::Vague(mir::VagueType::Unknown),
             InferredType::Static(type_kind) => type_kind.clone(),
             InferredType::OneOf(inferred_types) => {
                 let list: Vec<mir::TypeKind> =
-                    inferred_types.iter().map(|t| t.collapse(scope)).collect();
+                    inferred_types.iter().map(|t| t.collapse()).collect();
                 if let Some(first) = list.first() {
                     if list.iter().all(|i| i == first) {
                         first.clone().into()
                     } else {
-                        // IntoMIRError::ConflictingType(self.get_range())
-                        mir::TypeKind::Void
+                        mir::TypeKind::Vague(mir::VagueType::Unknown)
                     }
                 } else {
                     mir::TypeKind::Void
                 }
             }
             InferredType::Void => mir::TypeKind::Void,
+            InferredType::Unknown => mir::TypeKind::Vague(mir::VagueType::Unknown),
         }
     }
 }
 
-pub struct VirtualVariable {
-    name: String,
-    inferred: InferredType,
-}
-
-pub struct VirtualFunctionSignature {
-    name: String,
-    return_type: mir::TypeKind,
-    parameter_types: Vec<mir::TypeKind>,
-}
-
 pub struct VirtualStorage<T> {
     storage: HashMap<String, Vec<T>>,
 }
@@ -88,73 +66,8 @@ impl<T> Default for VirtualStorage<T> {
     }
 }
 
-pub struct VirtualScope {
-    variables: VirtualStorage<VirtualVariable>,
-    functions: VirtualStorage<VirtualFunctionSignature>,
-}
-
-impl VirtualScope {
-    pub fn set_var(&mut self, variable: VirtualVariable) {
-        self.variables.set(variable.name.clone(), variable);
-    }
-
-    pub fn set_fun(&mut self, function: VirtualFunctionSignature) {
-        self.functions.set(function.name.clone(), function)
-    }
-
-    pub fn get_var(&self, name: &String) -> Option<InferredType> {
-        self.variables.get(name).and_then(|v| {
-            if v.len() > 1 {
-                Some(InferredType::OneOf(
-                    v.iter().map(|v| v.inferred.clone()).collect(),
-                ))
-            } else if let Some(v) = v.first() {
-                Some(v.inferred.clone())
-            } else {
-                None
-            }
-        })
-    }
-
-    pub fn get_return_type(&self, name: &String) -> Option<mir::TypeKind> {
-        self.functions.get(name).and_then(|v| {
-            if v.len() > 1 {
-                Some(mir::TypeKind::Vague(mir::VagueType::Unknown))
-            } else if let Some(v) = v.first() {
-                Some(v.return_type.clone())
-            } else {
-                None
-            }
-        })
-    }
-}
-
-impl Default for VirtualScope {
-    fn default() -> Self {
-        Self {
-            variables: Default::default(),
-            functions: Default::default(),
-        }
-    }
-}
-
 impl ast::Module {
     pub fn process(&self) -> mir::Module {
-        let mut scope = VirtualScope::default();
-
-        for stmt in &self.top_level_statements {
-            match stmt {
-                FunctionDefinition(ast::FunctionDefinition(signature, _, _)) => {
-                    scope.set_fun(VirtualFunctionSignature {
-                        name: signature.name.clone(),
-                        return_type: signature.return_type.into(),
-                        parameter_types: signature.args.iter().map(|p| p.1.into()).collect(),
-                    });
-                }
-                _ => {}
-            }
-        }
-
         let mut imports = Vec::new();
         let mut functions = Vec::new();
 
@@ -167,13 +80,6 @@ impl ast::Module {
                     }
                 }
                 FunctionDefinition(ast::FunctionDefinition(signature, block, range)) => {
-                    for (name, ptype) in &signature.args {
-                        scope.set_var(VirtualVariable {
-                            name: name.clone(),
-                            inferred: InferredType::Static((*ptype).into()),
-                        });
-                    }
-
                     let def = mir::FunctionDefinition {
                         name: signature.name.clone(),
                         return_type: signature
@@ -186,10 +92,7 @@ impl ast::Module {
                             .cloned()
                             .map(|p| (p.0, p.1.into()))
                             .collect(),
-                        kind: mir::FunctionDefinitionKind::Local(
-                            block.into_mir(&mut scope),
-                            (*range).into(),
-                        ),
+                        kind: mir::FunctionDefinitionKind::Local(block.into_mir(), (*range).into()),
                     };
                     functions.push(def);
                 }
@@ -207,41 +110,33 @@ impl ast::Module {
 }
 
 impl ast::Block {
-    pub fn into_mir(&self, scope: &mut VirtualScope) -> mir::Block {
+    pub fn into_mir(&self) -> mir::Block {
         let mut mir_statements = Vec::new();
 
         for statement in &self.0 {
             let (kind, range) = match statement {
                 ast::BlockLevelStatement::Let(s_let) => {
-                    let t = s_let.1.infer_return_type().collapse(scope);
+                    let t = s_let.1.infer_return_type().collapse();
                     let inferred = InferredType::Static(t.clone());
-                    scope.set_var(VirtualVariable {
-                        name: s_let.0.clone(),
-                        inferred,
-                    });
 
                     (
                         mir::StmtKind::Let(
                             mir::VariableReference(t, s_let.0.clone(), s_let.2.into()),
-                            s_let.1.process(scope),
+                            s_let.1.process(),
                         ),
                         s_let.2,
                     )
                 }
                 ast::BlockLevelStatement::Import(_) => todo!(),
-                ast::BlockLevelStatement::Expression(e) => {
-                    (StmtKind::Expression(e.process(scope)), e.1)
-                }
-                ast::BlockLevelStatement::Return(_, e) => {
-                    (StmtKind::Expression(e.process(scope)), e.1)
-                }
+                ast::BlockLevelStatement::Expression(e) => (StmtKind::Expression(e.process()), e.1),
+                ast::BlockLevelStatement::Return(_, e) => (StmtKind::Expression(e.process()), e.1),
             };
 
             mir_statements.push(mir::Statement(kind, range.into()));
         }
 
         let return_expression = if let Some(r) = &self.1 {
-            Some((r.0.into(), Box::new(r.1.process(scope))))
+            Some((r.0.into(), Box::new(r.1.process())))
         } else {
             None
         };
@@ -271,40 +166,32 @@ impl From<ast::ReturnType> for mir::ReturnKind {
 }
 
 impl ast::Expression {
-    fn process(&self, scope: &mut VirtualScope) -> mir::Expression {
+    fn process(&self) -> mir::Expression {
         let kind = match &self.0 {
             ast::ExpressionKind::VariableName(name) => mir::ExprKind::Variable(VariableReference(
-                if let Some(ty) = scope.get_var(name) {
-                    ty.collapse(scope)
-                } else {
-                    mir::TypeKind::Vague(mir::VagueType::Unknown)
-                },
+                mir::TypeKind::Vague(mir::VagueType::Unknown),
                 name.clone(),
                 self.1.into(),
             )),
             ast::ExpressionKind::Literal(literal) => mir::ExprKind::Literal(literal.mir()),
             ast::ExpressionKind::Binop(binary_operator, lhs, rhs) => mir::ExprKind::BinOp(
                 binary_operator.mir(),
-                Box::new(lhs.process(scope)),
-                Box::new(rhs.process(scope)),
+                Box::new(lhs.process()),
+                Box::new(rhs.process()),
             ),
             ast::ExpressionKind::FunctionCall(fn_call_expr) => {
                 mir::ExprKind::FunctionCall(mir::FunctionCall {
                     name: fn_call_expr.0.clone(),
-                    return_type: if let Some(r_type) = scope.get_return_type(&fn_call_expr.0) {
-                        r_type
-                    } else {
-                        mir::TypeKind::Vague(mir::VagueType::Unknown)
-                    },
-                    parameters: fn_call_expr.1.iter().map(|e| e.process(scope)).collect(),
+                    return_type: mir::TypeKind::Vague(mir::VagueType::Unknown),
+                    parameters: fn_call_expr.1.iter().map(|e| e.process()).collect(),
                 })
             }
-            ast::ExpressionKind::BlockExpr(block) => mir::ExprKind::Block(block.into_mir(scope)),
+            ast::ExpressionKind::BlockExpr(block) => mir::ExprKind::Block(block.into_mir()),
             ast::ExpressionKind::IfExpr(if_expression) => {
-                let cond = if_expression.0.process(scope);
-                let then_block = if_expression.1.into_mir(scope);
+                let cond = if_expression.0.process();
+                let then_block = if_expression.1.into_mir();
                 let else_block = if let Some(el) = &if_expression.2 {
-                    Some(el.into_mir(scope))
+                    Some(el.into_mir())
                 } else {
                     None
                 };
@@ -371,12 +258,3 @@ impl From<ast::Type> for mir::TypeKind {
         value.0.into()
     }
 }
-
-impl From<Option<ast::Type>> for mir::TypeKind {
-    fn from(value: Option<ast::Type>) -> Self {
-        match value {
-            Some(v) => v.into(),
-            None => mir::TypeKind::Void,
-        }
-    }
-}

reid/src/lib.rs

@@ -7,6 +7,7 @@ mod codegen;
 mod lexer;
 pub mod mir;
 mod token_stream;
+mod util;
 
 // TODO:
 // 1. Make it so that TopLevelStatement can only be import or function def
@@ -20,6 +21,8 @@ pub enum ReidError {
     LexerError(#[from] lexer::Error),
     #[error(transparent)]
     ParserError(#[from] token_stream::Error),
+    #[error("Errors during typecheck: {0:?}")]
+    TypeCheckErrors(Vec<mir::typecheck::Error>),
     // #[error(transparent)]
     // CodegenError(#[from] codegen::Error),
 }
@@ -49,6 +52,14 @@ pub fn compile(source: &str) -> Result<String, ReidError> {
 
     dbg!(&mir_module);
 
+    let state = mir_module.typecheck();
+    dbg!(&state);
+    if !state.errors.is_empty() {
+        return Err(ReidError::TypeCheckErrors(state.errors));
+    }
+
+    dbg!(&mir_module);
+
     let mut context = Context::new();
     let codegen_module = mir_module.codegen(&mut context);
 

reid/src/mir/mod.rs

@@ -3,37 +3,51 @@
 /// type-checked beforehand.
 use crate::token_stream::TokenRange;
 
+pub mod typecheck;
 pub mod types;
 
-#[derive(Debug, Clone, Copy)]
+#[derive(Default, Debug, Clone, Copy)]
 pub struct Metadata {
     pub range: TokenRange,
 }
 
+impl std::fmt::Display for Metadata {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{:?}", self.range)
+    }
+}
+
+impl std::ops::Add for Metadata {
+    type Output = Metadata;
+
+    fn add(self, rhs: Self) -> Self::Output {
+        Metadata {
+            range: self.range + rhs.range,
+        }
+    }
+}
+
 impl From<TokenRange> for Metadata {
     fn from(value: TokenRange) -> Self {
         Metadata { range: value }
     }
 }
 
-impl Default for Metadata {
-    fn default() -> Self {
-        Metadata {
-            range: Default::default(),
-        }
-    }
-}
-
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, thiserror::Error)]
 pub enum TypeKind {
+    #[error("i32")]
     I32,
+    #[error("i16")]
     I16,
+    #[error("void")]
     Void,
-    Vague(VagueType),
+    #[error(transparent)]
+    Vague(#[from] VagueType),
 }
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, thiserror::Error)]
 pub enum VagueType {
+    #[error("Unknown")]
     Unknown,
 }
 
@@ -126,6 +140,22 @@ pub enum FunctionDefinitionKind {
     Extern,
 }
 
+impl FunctionDefinition {
+    fn block_meta(&self) -> Metadata {
+        match &self.kind {
+            FunctionDefinitionKind::Local(block, _) => block.meta,
+            FunctionDefinitionKind::Extern => Metadata::default(),
+        }
+    }
+
+    fn signature(&self) -> Metadata {
+        match &self.kind {
+            FunctionDefinitionKind::Local(_, metadata) => *metadata,
+            FunctionDefinitionKind::Extern => Metadata::default(),
+        }
+    }
+}
+
 #[derive(Debug)]
 pub struct Block {
     /// List of non-returning statements

reid/src/mir/typecheck.rs

@@ -0,0 +1,362 @@
+use std::{collections::HashMap, convert::Infallible, iter};
+
+/// This module contains code relevant to doing a type checking pass on the MIR.
+use crate::{mir::*, util::try_all};
+use TypeKind::*;
+use VagueType::*;
+
+#[derive(Debug, Clone)]
+pub struct Error {
+    metadata: Metadata,
+    kind: ErrorKind,
+}
+
+impl std::fmt::Display for Error {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "Error at {}: {}", self.metadata, self.kind)
+    }
+}
+
+impl std::error::Error for Error {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        self.kind.source()
+    }
+}
+
+#[derive(thiserror::Error, Debug, Clone)]
+pub enum ErrorKind {
+    #[error("NULL error, should never occur!")]
+    Null,
+    #[error("Type is vague: {0}")]
+    TypeIsVague(VagueType),
+    #[error("Types {0} and {1} are incompatible")]
+    TypesIncompatible(TypeKind, TypeKind),
+    #[error("Variable not defined: {0}")]
+    VariableNotDefined(String),
+    #[error("Function not defined: {0}")]
+    FunctionNotDefined(String),
+    #[error("Type is vague: {0}")]
+    ReturnTypeMismatch(TypeKind, TypeKind),
+}
+
+#[derive(Clone)]
+pub struct TypeStorage<T>(HashMap<String, T>);
+
+impl<T> Default for TypeStorage<T> {
+    fn default() -> Self {
+        Self(Default::default())
+    }
+}
+
+impl<T: Collapsable> TypeStorage<T> {
+    fn set(&mut self, key: String, value: T) -> Result<T, ErrorKind> {
+        if let Some(inner) = self.0.get(&key) {
+            match value.collapse_into(inner) {
+                Ok(collapsed) => {
+                    self.0.insert(key, collapsed.clone());
+                    Ok(collapsed)
+                }
+                Err(e) => Err(e),
+            }
+        } else {
+            self.0.insert(key, value.clone());
+            Ok(value)
+        }
+    }
+
+    fn get(&self, key: &String) -> Option<&T> {
+        self.0.get(key)
+    }
+}
+
+#[derive(Debug)]
+pub struct State {
+    pub errors: Vec<Error>,
+}
+
+impl State {
+    fn new() -> State {
+        State {
+            errors: Default::default(),
+        }
+    }
+
+    fn or_else<T: Into<Metadata> + Clone + Copy>(
+        &mut self,
+        result: Result<TypeKind, ErrorKind>,
+        default: TypeKind,
+        meta: T,
+    ) -> TypeKind {
+        match result {
+            Ok(t) => t,
+            Err(e) => {
+                self.errors.push(Error {
+                    metadata: meta.into(),
+                    kind: e,
+                });
+                default
+            }
+        }
+    }
+
+    fn ok<T: Into<Metadata> + Clone + Copy, U>(&mut self, result: Result<U, ErrorKind>, meta: T) {
+        if let Err(e) = result {
+            self.errors.push(Error {
+                metadata: meta.into(),
+                kind: e,
+            });
+        }
+    }
+}
+
+#[derive(Clone, Default)]
+pub struct Scope {
+    function_returns: TypeStorage<ScopeFunction>,
+    variables: TypeStorage<TypeKind>,
+}
+
+#[derive(Clone)]
+pub struct ScopeFunction {
+    ret: TypeKind,
+    params: Vec<TypeKind>,
+}
+
+impl Scope {
+    fn inner(&self) -> Scope {
+        Scope {
+            function_returns: self.function_returns.clone(),
+            variables: self.variables.clone(),
+        }
+    }
+}
+
+#[derive(Clone)]
+pub enum Inferred {
+    Type(TypeKind),
+    Unresolved(u32),
+}
+
+impl Module {
+    pub fn typecheck(&self) -> State {
+        let mut state = State::new();
+        let mut scope = Scope::default();
+
+        for function in &self.functions {
+            let r = scope.function_returns.set(
+                function.name.clone(),
+                ScopeFunction {
+                    ret: function.return_type,
+                    params: function.parameters.iter().map(|v| v.1).collect(),
+                },
+            );
+        }
+
+        for function in &self.functions {
+            let res = function.typecheck(&mut state, &mut scope);
+            state.ok(res, function.block_meta());
+        }
+
+        state
+    }
+}
+
+impl FunctionDefinition {
+    fn typecheck(&self, state: &mut State, scope: &mut Scope) -> Result<TypeKind, ErrorKind> {
+        for param in &self.parameters {
+            let param_t = state.or_else(param.1.assert_known(), Vague(Unknown), self.signature());
+            state.ok(
+                scope.variables.set(param.0.clone(), param_t),
+                self.signature(),
+            );
+        }
+
+        let return_type = self.return_type.clone();
+        dbg!(&return_type);
+        let inferred = match &self.kind {
+            FunctionDefinitionKind::Local(block, _) => block.typecheck(state, scope),
+            FunctionDefinitionKind::Extern => Ok(Vague(Unknown)),
+        };
+        dbg!(&inferred);
+
+        match inferred {
+            Ok(t) => try_collapse(&return_type, &t)
+                .or(Err(ErrorKind::ReturnTypeMismatch(return_type, t))),
+            Err(e) => Ok(state.or_else(Err(e), return_type, self.block_meta())),
+        }
+    }
+}
+
+impl Block {
+    fn typecheck(&self, state: &mut State, scope: &mut Scope) -> Result<TypeKind, ErrorKind> {
+        let mut scope = scope.inner();
+
+        for statement in &self.statements {
+            match &statement.0 {
+                StmtKind::Let(variable_reference, expression) => {
+                    let res = expression.typecheck(state, &mut scope);
+
+                    // If expression resolution itself was erronous, resolve as
+                    // Unknown.
+                    let res = state.or_else(res, Vague(Unknown), expression.1);
+
+                    // Make sure the expression and variable type really is the same
+                    state.ok(
+                        res.collapse_into(&variable_reference.0),
+                        variable_reference.2 + expression.1,
+                    );
+
+                    // TODO make sure expression/variable type is NOT vague anymore
+
+                    // Variable might already be defined, note error
+                    state.ok(
+                        scope
+                            .variables
+                            .set(variable_reference.1.clone(), variable_reference.0),
+                        variable_reference.2,
+                    );
+                }
+                StmtKind::Import(_) => todo!(),
+                StmtKind::Expression(expression) => {
+                    let res = expression.typecheck(state, &mut scope);
+                    state.ok(res, expression.1);
+                }
+            }
+        }
+
+        if let Some((_, expr)) = &self.return_expression {
+            let res = expr.typecheck(state, &mut scope);
+            Ok(state.or_else(res, Vague(Unknown), expr.1))
+        } else {
+            Ok(Void)
+        }
+    }
+}
+
+impl Expression {
+    fn typecheck(&self, state: &mut State, scope: &mut Scope) -> Result<TypeKind, ErrorKind> {
+        match &self.0 {
+            ExprKind::Variable(var_ref) => {
+                let existing = state.or_else(
+                    scope
+                        .variables
+                        .get(&var_ref.1)
+                        .copied()
+                        .ok_or(ErrorKind::VariableNotDefined(var_ref.1.clone())),
+                    Vague(Unknown),
+                    var_ref.2,
+                );
+
+                Ok(state.or_else(
+                    var_ref.0.collapse_into(&existing),
+                    Vague(Unknown),
+                    var_ref.2,
+                ))
+            }
+            ExprKind::Literal(literal) => Ok(literal.as_type()),
+            ExprKind::BinOp(_, lhs, rhs) => {
+                // TODO make sure lhs and rhs can actually do this binary
+                // operation once relevant
+                let lhs_res = lhs.typecheck(state, scope);
+                let rhs_res = rhs.typecheck(state, scope);
+                let lhs_type = state.or_else(lhs_res, Vague(Unknown), lhs.1);
+                let rhs_type = state.or_else(rhs_res, Vague(Unknown), rhs.1);
+                lhs_type.collapse_into(&rhs_type)
+            }
+            ExprKind::FunctionCall(function_call) => {
+                let true_function = scope
+                    .function_returns
+                    .get(&function_call.name)
+                    .cloned()
+                    .ok_or(ErrorKind::FunctionNotDefined(function_call.name.clone()));
+
+                if let Ok(f) = true_function {
+                    if function_call.parameters.len() != f.params.len() {
+                        state.ok::<_, Infallible>(Err(ErrorKind::Null), self.1);
+                    }
+
+                    let true_params_iter = f.params.into_iter().chain(iter::repeat(Vague(Unknown)));
+
+                    for (param, true_param_t) in
+                        function_call.parameters.iter().zip(true_params_iter)
+                    {
+                        let param_res = param.typecheck(state, scope);
+                        let param_t = state.or_else(param_res, Vague(Unknown), param.1);
+                        state.ok(param_t.collapse_into(&true_param_t), param.1);
+                    }
+
+                    // Make sure function return type is the same as the claimed
+                    // return type
+                    // TODO: Set return type here actually
+                    try_collapse(&f.ret, &function_call.return_type)
+                } else {
+                    Ok(function_call.return_type)
+                }
+            }
+            ExprKind::If(IfExpression(cond, lhs, rhs)) => {
+                // TODO make sure cond_res is Boolean here
+                let cond_res = cond.typecheck(state, scope);
+                state.ok(cond_res, cond.1);
+
+                let lhs_res = lhs.typecheck(state, scope);
+                let lhs_type = state.or_else(lhs_res, Vague(Unknown), lhs.meta);
+                let rhs_type = if let Some(rhs) = rhs {
+                    let res = rhs.typecheck(state, scope);
+                    state.or_else(res, Vague(Unknown), rhs.meta)
+                } else {
+                    Vague(Unknown)
+                };
+                lhs_type.collapse_into(&rhs_type)
+            }
+            ExprKind::Block(block) => block.typecheck(state, scope),
+        }
+    }
+}
+
+impl TypeKind {
+    fn assert_known(&self) -> Result<TypeKind, ErrorKind> {
+        if let Vague(vague) = self {
+            Err(ErrorKind::TypeIsVague(*vague))
+        } else {
+            Ok(*self)
+        }
+    }
+}
+
+fn try_collapse(lhs: &TypeKind, rhs: &TypeKind) -> Result<TypeKind, ErrorKind> {
+    lhs.collapse_into(rhs)
+        .or(rhs.collapse_into(lhs))
+        .or(Err(ErrorKind::TypesIncompatible(*lhs, *rhs)))
+}
+
+trait Collapsable: Sized + Clone {
+    fn collapse_into(&self, other: &Self) -> Result<Self, ErrorKind>;
+}
+
+impl Collapsable for TypeKind {
+    fn collapse_into(&self, other: &TypeKind) -> Result<TypeKind, ErrorKind> {
+        if self == other {
+            return Ok(self.clone());
+        }
+
+        match (self, other) {
+            (Vague(Unknown), other) | (other, Vague(Unknown)) => Ok(other.clone()),
+            _ => Err(ErrorKind::TypesIncompatible(*self, *other)),
+        }
+    }
+}
+
+impl Collapsable for ScopeFunction {
+    fn collapse_into(&self, other: &ScopeFunction) -> Result<ScopeFunction, ErrorKind> {
+        Ok(ScopeFunction {
+            ret: self.ret.collapse_into(&other.ret)?,
+            params: try_all(
+                self.params
+                    .iter()
+                    .zip(&other.params)
+                    .map(|(p1, p2)| p1.collapse_into(&p2))
+                    .collect(),
+            )
+            .map_err(|e| e.first().unwrap().clone())?,
+        })
+    }
+}

reid/src/token_stream.rs

@@ -156,7 +156,7 @@ impl Drop for TokenStream<'_, '_> {
     }
 }
 
-#[derive(Clone, Copy)]
+#[derive(Default, Clone, Copy)]
 pub struct TokenRange {
     pub start: usize,
     pub end: usize,
@@ -168,15 +168,6 @@ impl std::fmt::Debug for TokenRange {
     }
 }
 
-impl Default for TokenRange {
-    fn default() -> Self {
-        Self {
-            start: Default::default(),
-            end: Default::default(),
-        }
-    }
-}
-
 impl std::ops::Add for TokenRange {
     type Output = TokenRange;
 

reid/src/util.rs

@@ -0,0 +1,17 @@
+pub fn try_all<U, E>(list: Vec<Result<U, E>>) -> Result<Vec<U>, Vec<E>> {
+    let mut successes = Vec::with_capacity(list.len());
+    let mut failures = Vec::with_capacity(list.len());
+
+    for item in list {
+        match item {
+            Ok(s) => successes.push(s),
+            Err(e) => failures.push(e),
+        }
+    }
+
+    if failures.len() > 0 {
+        Err(failures)
+    } else {
+        Ok(successes)
+    }
+}