got type system working

examples/math/main.bl

@@ -1,14 +1,14 @@
 // adds a and b, but also 4 for some reason
-fn add(a: I32, b: I32): I32 {
+fn add(a: I64, b: I64): I64 {
     let foo = 4; // because I feel like it
-    let test_float: F32 = {
+    let test_float: F64 = {
       10.2
     };
     test_float = 5.0;
     a + b + foo
 }
 
-fn subtract(a: I32, b: I32): I32 {
+fn subtract(a: I64, b: I64): I64 {
     a - b
 }
 
@@ -25,10 +25,10 @@ fn i_hate_this(a: F64): F64 {
 }
 
 fn unit_function() {
-  let a: I32 = 4;
+  let a: I64 = 4;
 }
 
-fn main(): I32 {
+fn main(): I64 {
     add(4, subtract(5, 2))
 }
 
@@ -39,28 +39,28 @@ fn returns_user(): User {
     };
 }
 
-fn get_user_id(): U64 {
+fn get_user_id(): I64 {
     let user = returns_user();
     user.id = 5;
     return user.id;
 }
 
-fn use_method(user: User): U64 {
+fn use_method(user: User): I64 {
     return user.get_id();
 }
 
 type User struct {
-    id: U64,
+    id: I64,
 }
 
 impl User {
-    fn new(id: U64): Self {
+    fn new(id: I64): Self {
         return Self{
             id: id,
         };
     }
 
-    fn get_id(self: Self): U64 {
+    fn get_id(self: Self): I64 {
         return self.id;
     }
 }

src/grammar.lalrpop

@@ -37,7 +37,7 @@ pub LiteralInt: String = {
 };
 
 pub SpannedLiteralInt: ast::LiteralInt = {
-    <literal_int:Spanned<LiteralInt>> => ast::LiteralInt{value: literal_int, type_: ast::TypeUsage::new_builtin("i64".to_string())}
+    <literal_int:Spanned<LiteralInt>> => ast::LiteralInt{value: literal_int, type_: ast::TypeUsage::new_builtin("I64".to_string())}
 };
 
 pub LiteralFloat: String = {
@@ -45,7 +45,7 @@ pub LiteralFloat: String = {
 };
 
 pub SpannedLiteralFloat: ast::LiteralFloat = {
-    <literal_float:Spanned<LiteralFloat>> => ast::LiteralFloat{value: literal_float, type_: ast::TypeUsage::new_builtin("f64".to_string())}
+    <literal_float:Spanned<LiteralFloat>> => ast::LiteralFloat{value: literal_float, type_: ast::TypeUsage::new_builtin("F64".to_string())}
 };
 
 pub Identifier: String = {
@@ -149,7 +149,7 @@ pub Statement: ast::Statement = {
 
 pub Block: ast::Block = {
     "{" <v:(<Statement>)*> <e:Expression?> "}" => match e {
-        None => ast::Block{statements: v, type_: ast::new_never()},
+        None => ast::Block{statements: v, type_: ast::TypeUsage::new_unknown(&id_generator)},
         Some(e) => {
             let mut v = v;
             v.push(ast::Statement::Expression(e));
@@ -160,7 +160,7 @@ pub Block: ast::Block = {
 
 pub TypeUsage: ast::TypeUsage = {
     <n:SpannedIdentifier> => ast::TypeUsage::Named(ast::NamedTypeUsage{name: n}),
-    "fn" "(" <args:Comma<TypeUsage>> ")" => ast::TypeUsage::Function(ast::FunctionTypeUsage{arguments: args, return_type: Box::new(ast::TypeUsage::new_unknown(&id_generator))}),
+    "fn" "(" <args:Comma<TypeUsage>> ")" => ast::TypeUsage::Function(ast::FunctionTypeUsage{arguments: args, return_type: Box::new(ast::new_unit())}),
     "fn" "(" <args:Comma<TypeUsage>> ")" ":" <rt:TypeUsage> => ast::TypeUsage::Function(ast::FunctionTypeUsage{arguments: args, return_type: Box::new(rt)}),
 };
 
@@ -169,7 +169,7 @@ pub VariableDeclaration: ast::VariableDeclaration = {
 };
 
 pub FunctionDeclaration: ast::FunctionDeclaration = {
-    "fn" <n:SpannedIdentifier> "(" <args:Comma<VariableDeclaration>> ")" => ast::FunctionDeclaration{name: n, arguments: args, return_type: ast::TypeUsage::new_unknown(&id_generator)},
+    "fn" <n:SpannedIdentifier> "(" <args:Comma<VariableDeclaration>> ")" => ast::FunctionDeclaration{name: n, arguments: args, return_type: ast::new_unit()},
     "fn" <n:SpannedIdentifier> "(" <args:Comma<VariableDeclaration>> ")" ":" <rt:TypeUsage> => ast::FunctionDeclaration{name: n, arguments: args, return_type: rt},
 };
 

src/main.rs

@@ -48,7 +48,7 @@ fn main() {
     println!("resolved ast: {:#?}", &resolved_ast);
     let type_checker = type_checking::TypeChecker{};
     let (checked_ast, subst) = type_checker.with_module(&resolved_ast);
-    println!("checked ast: {:#?}", &resolved_ast);
+    println!("checked ast: {:#?}", &checked_ast);
     println!("substitutions: {:#?}", &subst);
 
     // let context = Context::create();

src/type_alias_resolution.rs

@@ -212,8 +212,13 @@ impl TypeAliasResolver {
                     })
                 },
                 ast::Subexpression::LiteralStruct(literal_struct) => {
+                    let result = resolve_type(ctx, &ast::NamedTypeUsage{name: literal_struct.name.clone()});
+                    let new_name = match &result {
+                        ast::TypeUsage::Named(named) => { named.name.clone() },
+                        _ => panic!("LiteralStruct resolved to non-named-type"),
+                    };
                     ast::Subexpression::LiteralStruct(ast::LiteralStruct{
-                        name: literal_struct.name.clone(),
+                        name: new_name.clone(),
                         fields: literal_struct.fields.iter().map(|field|{
                             (field.0.clone(), self.with_expression(ctx, &field.1))
                         }).collect(),

src/type_checking.rs

@@ -4,34 +4,36 @@ use crate::ast;
 
 pub type SubstitutionMap = HashMap<String, ast::TypeUsage>;
 
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub enum NamedEntity {
     TypeDeclaration(ast::TypeDeclaration),
     Variable(ast::TypeUsage),
 }
 
 
-#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+#[derive(Debug, Clone, PartialEq, Eq)]
 struct Context {
     pub current_function_return: Option<ast::TypeUsage>,
-    pub environment: HashMap<String, ast::NamedEntity>,
+    pub impls: HashMap<String, ast::Impl>,
+    pub environment: HashMap<String, NamedEntity>,
 }
 
 impl Context {
     fn add_variable(&self, name: String, type_usage: &ast::TypeUsage) -> Context {
         let mut ctx = self.clone();
-        ctx.environment[name] = NamedEntity::Variable(type_usage.clone());
+        ctx.environment.insert(name.to_string(), NamedEntity::Variable(type_usage.clone()));
         return ctx;
     }
 
     fn add_type(&self, name: String, type_decl: &ast::TypeDeclaration) -> Context {
         let mut ctx = self.clone();
-        ctx.environment[name] = NamedEntity::TypeDeclaration(type_decl.clone());
+        ctx.environment.insert(name.to_string(), NamedEntity::TypeDeclaration(type_decl.clone()));
         return ctx;
     }
 
-    fn set_current_function_return(&self, function: ast::TypeUsage) -> Context {
+    fn set_current_function_return(&self, function: &ast::TypeUsage) -> Context {
         let mut ctx = self.clone();
-        ctx.current_function_return = Some(function);
+        ctx.current_function_return = Some(function.clone());
         return ctx;
     }
 }
@@ -40,75 +42,90 @@ fn apply_substitution(substitution: &SubstitutionMap, type_: &ast::TypeUsage) ->
     match type_ {
         ast::TypeUsage::Named(named) => ast::TypeUsage::Named(named.clone()),
         ast::TypeUsage::Unknown(unknown) => {
-            if substitution.contains_key(unknown.name) {
-                ast::TypeUsage::Unknown(substitution[unknown.name].clone())
+            if substitution.contains_key(&unknown.name) {
+                substitution[&unknown.name].clone()
             } else {
                 ast::TypeUsage::Unknown(unknown.clone())
             }
         },
         ast::TypeUsage::Function(function) => {
-            ast::TypeUsage::Function(FunctionTypeUsage{
+            ast::TypeUsage::Function(ast::FunctionTypeUsage{
                 arguments: function.arguments.iter().map(|arg| {
                     apply_substitution(substitution, arg)
                 }).collect(),
-                return_type: apply_substitution(substitution, function.return_type),
+                return_type: Box::new(apply_substitution(substitution, &function.return_type)),
             })
         }
     }
 }
 
-fn compose_substitutions(s1: SubstitutionMap, s2: SubstitutionMap) -> SubstitutionMap {
+fn compose_substitutions(s1: &SubstitutionMap, s2: &SubstitutionMap) -> SubstitutionMap {
     let mut result = SubstitutionMap::new();
     for k in s2.keys() {
-        result[k] = apply_substitution(s1, s2[k]);
+        result.insert(k.to_string(), apply_substitution(s1, &s2[k]));
     }
-    return s1.into_iter().chain(result).collect();
+    return s1.into_iter().map(|(k, v)| (k.clone(), v.clone())).chain(result).collect();
 }
 
-fn unify(t1: ast::TypeUsage, t2: ast::TypeUsage) -> SubstitutionMap {
+fn unify(t1: &ast::TypeUsage, t2: &ast::TypeUsage) -> SubstitutionMap {
     match (t1, t2) {
         (ast::TypeUsage::Named(named1), ast::TypeUsage::Named(named2)) => {
+            // if named1.name.name.value == "!" || named2.name.name.value == "!" {
+            //     return SubstitutionMap::new(); // never matches with everything
+            // }
             if named1.name.name.value == named2.name.name.value {
-                return SubstitutionMap::new()
+                return SubstitutionMap::new();
             }
         },
         _ => {},
     }
-    if let ast::TypeUsage::Unknown(unknown) = t1 {
-        return var_bind(unknown.name, t2);
+    match t1 {
+        ast::TypeUsage::Unknown(unknown) => {
+            return var_bind(&unknown.name, t2);
+        },
+        _ => {},
     }
-    if let ast::TypeUsage::Unknown(unknown) = t2 {
-        return var_bind(unknown.name, t1);
+    match t2 {
+        ast::TypeUsage::Unknown(unknown) => {
+            return var_bind(&unknown.name, t1);
+        },
+        _ => {},
     }
     match (t1, t2) {
         (ast::TypeUsage::Function(f1), ast::TypeUsage::Function(f2)) => {
-            let mut result = unify(f1.return_type, f2.return_type);
+            let mut result = unify(&*f1.return_type, &*f2.return_type);
             if f1.arguments.len() != f2.arguments.len() {
                 panic!("Argument lengths don't match");
             }
             for (i, _) in f1.arguments.iter().enumerate() {
-                result = compose_substitutions(result, unify(apply_substitution(result, f1.arguments[i]), apply_substitution(result, f2.arguments[i])));
+                result = compose_substitutions(&result, &unify(&apply_substitution(&result, &f1.arguments[i]), &apply_substitution(&result, &f2.arguments[i])));
             }
             return result;
         },
         _ => {},
     }
+    println!("problem:\n{:?}\n{:?}", t1, t2);
     panic!("Mismatched unification types");
 }
 
-fn var_bind(name: &str, t: ast::TypeUsage) -> SubstitutionMap {
-    if let ast::TypeUsage::Unknown(unknown) = t && name == unknown.name {
-        return SubstitutionMap::new();
+fn var_bind(name: &str, t: &ast::TypeUsage) -> SubstitutionMap {
+    match t {
+        ast::TypeUsage::Unknown(unknown) => {
+            if name == unknown.name {
+                return SubstitutionMap::new();
+            }
+        },
+        _ => {}
     }
     if contains(t, name) {
         panic!("Type contains a reference to itself")
     }
     let mut substitution = SubstitutionMap::new();
-    substitution[name] = t;
+    substitution.insert(name.to_string(), t.clone());
     return substitution;
 }
 
-fn contains(t: ast::TypeUsage, name: &str) -> bool {
+fn contains(t: &ast::TypeUsage, name: &str) -> bool {
     match t {
         ast::TypeUsage::Named(_) => {
             return false
@@ -117,11 +134,11 @@ fn contains(t: ast::TypeUsage, name: &str) -> bool {
             unknown.name == name
         },
         ast::TypeUsage::Function(f) => {
-            if contains(f.return_type, name) {
+            if contains(&*f.return_type, name) {
                 return true;
             }
             for arg in f.arguments.iter() {
-                if contains(arg, name) {
+                if contains(&arg.clone(), name) {
                     return true;
                 }
             }
@@ -137,46 +154,77 @@ impl TypeChecker {
     pub fn with_module(self: &Self, module: &ast::Module) -> (ast::Module, SubstitutionMap) {
         let mut ctx = Context{
             environment: HashMap::new(), //TODO: builtins
+            impls: HashMap::new(),
+            current_function_return: None,
         };
 
         for item in module.items.iter() {
             match item {
                 ast::ModuleItem::TypeDeclaration(ast::TypeDeclaration::Struct(struct_)) => {
-                    ctx.declarations.push(ast::NamedEntity::TypeDeclaration(ast::TypeDeclaration::Struct(struct_.clone())));
+                    ctx.environment.insert(struct_.name.name.value.to_string(), NamedEntity::TypeDeclaration(ast::TypeDeclaration::Struct(struct_.clone())));
                 },
                 ast::ModuleItem::TypeDeclaration(ast::TypeDeclaration::Alias(alias)) => {
-                    ctx.declarations.push(ast::NamedEntity::TypeDeclaration(ast::TypeDeclaration::Alias(alias.clone())));
+                    ctx.environment.insert(alias.name.name.value.to_string(), NamedEntity::TypeDeclaration(ast::TypeDeclaration::Alias(alias.clone())));
+                },
+                ast::ModuleItem::Function(function) => {
+                    let function_type = ast::FunctionTypeUsage{
+                        arguments: function.declaration.arguments.iter().map(|arg|{arg.type_.clone()}).collect(),
+                        return_type: Box::new(function.declaration.return_type.clone()),
+                    };
+                    ctx.environment.insert(function.declaration.name.name.value.to_string(), NamedEntity::Variable(ast::TypeUsage::Function(function_type)));
+                },
+                ast::ModuleItem::Impl(impl_) => {
+                    ctx.impls.insert(impl_.struct_name.name.value.to_string(), impl_.clone());
                 },
                 _ => {},
             }
         }
 
-        return ast::Module{
+        let mut subst = SubstitutionMap::new();
+        let result = ast::Module{
             items: module.items.iter().map(|item|{
                 match item {
                     ast::ModuleItem::Function(function) => {
-                        ast::ModuleItem::Function(self.with_function(&ctx, function))
+                        let (func, fn_subst) = self.with_function(&ctx, &subst, function);
+                        subst = compose_substitutions(&subst, &fn_subst);
+                        ast::ModuleItem::Function(func)
                     },
                     ast::ModuleItem::TypeDeclaration(type_declaration) => {
-                        ast::ModuleItem::TypeDeclaration(self.with_type_declaration(&ctx, type_declaration))
+                        let (ty_decl, ty_subst) = self.with_type_declaration(&ctx, type_declaration);
+                        subst = compose_substitutions(&subst, &ty_subst);
+                        ast::ModuleItem::TypeDeclaration(ty_decl)
                     },
                     ast::ModuleItem::Impl(impl_) => {
-                        ast::ModuleItem::Impl(self.with_impl(&ctx, impl_))
+                        let (impl_result, impl_subst) = self.with_impl(&ctx, &subst, impl_);
+                        subst = compose_substitutions(&subst, &impl_subst);
+                        ast::ModuleItem::Impl(impl_result)
                     },
                 }
             }).collect()
         };
+        return (result, subst);
     }
 
-    fn with_function(self: &Self, ctx: &Context, function: &ast::Function) -> (ast::Function, SubstitutionMap) {
+    fn with_function(self: &Self, ctx: &Context, incoming_substitutions: &SubstitutionMap, function: &ast::Function) -> (ast::Function, SubstitutionMap) {
         // add args to env
-        let mut function_ctx = ctx.set_current_function_return(function.declaration.return_type.clone());
+        let mut function_ctx = ctx.set_current_function_return(&function.declaration.return_type.clone());
         for arg in function.declaration.arguments.iter() {
-            function_ctx = function_ctx.add_variable(arg.name.to_string(), arg.type_.clone());
+            function_ctx = function_ctx.add_variable(arg.name.name.value.to_string(), &arg.type_.clone());
+        }
+
+        let (block, substitution) = self.with_block(&function_ctx, incoming_substitutions, &function.block);
+        let mut substitution = compose_substitutions(incoming_substitutions, &substitution);
+        match &block.type_ {
+            ast::TypeUsage::Named(named) => {
+                if named.name.name.value != "!" {
+                    substitution = compose_substitutions(&substitution, &unify(&function.declaration.return_type, &block.type_));
+                }
+            },
+            _ => {
+                substitution = compose_substitutions(&substitution, &unify(&function.declaration.return_type, &block.type_));
+            }
         }
 
-        let (block, substitution) = self.with_block(function_ctx, &function.block);
-        let substitution = unify(block.type_, function.declaration.return_type);
 
         return (ast::Function{
             declaration: ast::FunctionDeclaration{
@@ -193,8 +241,8 @@ impl TypeChecker {
     fn with_type_declaration(self: &Self, ctx: &Context, type_declaration: &ast::TypeDeclaration) -> (ast::TypeDeclaration, SubstitutionMap) {
         match type_declaration {
             ast::TypeDeclaration::Struct(struct_) => {
-                let (result, substitution) = self.with_struct_declaration(ctx, struct_);
-                return (ast::TypeDeclaration::Struct(result), substitution);
+                let result = self.with_struct_declaration(ctx, struct_);
+                return (ast::TypeDeclaration::Struct(result), SubstitutionMap::new());
             },
             ast::TypeDeclaration::Primitive(primitive) => {
                 return (ast::TypeDeclaration::Primitive(primitive.clone()), SubstitutionMap::new());
@@ -217,174 +265,327 @@ impl TypeChecker {
         };
     }
 
-    fn with_impl(self: &Self, ctx: &Context, impl_: &ast::Impl) -> (ast::Impl, SubstitutionMap) {
-        let mut substitutions = SubstitutionMap::new();
+    fn with_impl(self: &Self, ctx: &Context, incoming_substitutions: &SubstitutionMap, impl_: &ast::Impl) -> (ast::Impl, SubstitutionMap) {
+        let mut substitutions = incoming_substitutions.clone();
         return (ast::Impl{
             struct_name: impl_.struct_name.clone(),
             functions: impl_.functions.iter().map(|f|{
-                let (result, function_subs) = self.with_function(&ctx, f);
-                substitutions = compose_substitutions(substitutions, function_subs)
+                let (result, function_subs) = self.with_function(&ctx, &substitutions, f);
+                substitutions = compose_substitutions(&substitutions, &function_subs);
                 result
             }).collect(),
         }, substitutions);
     }
 
-    fn with_block(self: &Self, ctx: &Context, block: &ast::Block) -> (ast::Block, SubstitutionMap) {
-        let mut substitutions = SubstitutionMap::new();
+    fn with_block(self: &Self, ctx: &Context, incoming_substitutions: &SubstitutionMap, block: &ast::Block) -> (ast::Block, SubstitutionMap) {
+        let mut substitutions = incoming_substitutions.clone();
         let mut block_ctx = ctx.clone();
-        return ast::Block{
-            statements: block.statements.iter().map(|s| {
-                let (statement_ctx, result, statement_substitutions) = self.with_statement(block_ctx, s);
-                block_ctx = statement_ctx
-                substitutions = compose_substitutions(substitutions, statement_substitutions);
-                result
-            }).collect(),
-            type_: block.type_.clone(),
+        // if return it's always never
+        // if last is expression it's that else unit
+        let mut has_return = false;
+        for statement in block.statements.iter() {
+            match statement {
+                ast::Statement::Return(_) => {
+                    has_return = true;
+                },
+                _ => {}
+            }
+        }
+        let statements = block.statements.iter().map(|s| {
+            let (statement_ctx, result, statement_substitutions) = self.with_statement(&block_ctx, &substitutions, s);
+            block_ctx = statement_ctx;
+            substitutions = compose_substitutions(&substitutions, &statement_substitutions);
+            result
+        }).collect();
+        if !has_return {
+            match block.statements.last().unwrap() {
+                ast::Statement::Expression(expr) => {
+                    substitutions = compose_substitutions(&substitutions, &unify(&block.type_, &expr.type_));
+                },
+                _ => {
+                    substitutions = compose_substitutions(&substitutions, &unify(&block.type_, &ast::new_unit()));
+                }
+            }
+        }
+        let result_type = if has_return {
+            ast::new_never()
+        } else {
+            apply_substitution(&substitutions, &block.type_)
         };
+        let block_result = ast::Block{
+            statements: statements,
+            type_: result_type,
+        };
+        return (block_result, substitutions);
     }
 
-    fn with_statement(self: &Self, ctx: &Context, statement: &ast::Statement) -> (Context, ast::Statement, SubstitutionMap) {
-
+    fn with_statement(self: &Self, ctx: &Context, incoming_substitutions: &SubstitutionMap, statement: &ast::Statement) -> (Context, ast::Statement, SubstitutionMap) {
         match statement {
             ast::Statement::Return(return_statement) => {
-                let (result, subst) = self.with_return_statement(ctx, return_statement);
+                let (result, subst) = self.with_return_statement(ctx, incoming_substitutions, return_statement);
+                let subst = compose_substitutions(&incoming_substitutions, &subst);
                 return (ctx.clone(), ast::Statement::Return(result), subst);
             },
             ast::Statement::Let(let_statement) => {
-                let (let_ctx, result, subst) = self.with_let_statement(ctx, let_statement);
+                let (let_ctx, result, subst) = self.with_let_statement(ctx, incoming_substitutions, let_statement);
+                let subst = compose_substitutions(&incoming_substitutions, &subst);
                 return (let_ctx, ast::Statement::Let(result), subst);
             },
             ast::Statement::Assignment(assignment_statement) => {
-                let (result, subst) = self.with_assignment_statement(ctx, assignment_statement);
+                let (result, subst) = self.with_assignment_statement(ctx, incoming_substitutions, assignment_statement);
+                let subst = compose_substitutions(&incoming_substitutions, &subst);
                 return (ctx.clone(), ast::Statement::Assignment(result), subst);
             },
             ast::Statement::Expression(expression) => {
-                let (result, subst) = self.with_expression(ctx, expression);
+                let (result, subst) = self.with_expression(ctx, incoming_substitutions, expression);
+                let subst = compose_substitutions(&incoming_substitutions, &subst);
                 return (ctx.clone(), ast::Statement::Expression(result), subst);
             },
         }
     }
 
-    fn with_return_statement(self: &Self, ctx: &Context, statement: &ast::ReturnStatement) -> (ast::ReturnStatement, SubstitutionMap) {
-        let (result, subst) = self.with_expression(ctx, &statement.source);
-        let substitution = compose_substitutions(subst, unify(result.type_, ctx.current_function_return));
+    fn with_return_statement(self: &Self, ctx: &Context, incoming_substitutions: &SubstitutionMap, statement: &ast::ReturnStatement) -> (ast::ReturnStatement, SubstitutionMap) {
+        let (result, subst) = self.with_expression(ctx, incoming_substitutions, &statement.source);
+        let mut substitution = compose_substitutions(&incoming_substitutions, &subst);
+        let mut is_never = false;
+        match &result.type_ {
+            ast::TypeUsage::Named(named) => {
+                if named.name.name.value == "!" {
+                    is_never = true;
+                }
+            },
+            _ => {},
+        }
+        if !is_never {
+            substitution = compose_substitutions(&subst, &unify(&ctx.current_function_return.as_ref().unwrap(), &result.type_));
+        }
+
         return (ast::ReturnStatement{
             source: result,
         }, substitution);
     }
 
-    fn with_let_statement(self: &Self, ctx: &Context, statement: &ast::LetStatement) -> (Context, ast::LetStatement, SubstitutionMap) {
-        let (result, subst) = self.with_expression(ctx, &statement.expression);
-        let let_ctx = ctx.add_variable(statement.variable_name.clone(), result.type_);
-        let substitution = compose_substitutions(subst, unify(&statement.type_, result.type_));
+    fn with_let_statement(self: &Self, ctx: &Context, incoming_substitutions: &SubstitutionMap, statement: &ast::LetStatement) -> (Context, ast::LetStatement, SubstitutionMap) {
+        let (result, subst) = self.with_expression(ctx, incoming_substitutions, &statement.expression);
+        let let_ctx = ctx.add_variable(statement.variable_name.name.value.clone(), &result.type_);
+        let substitution = compose_substitutions(&subst, &unify(&statement.type_, &result.type_));
         return (let_ctx, ast::LetStatement{
             variable_name: statement.variable_name.clone(),
             expression: result,
-            type_: &statement.type_.clone(),
+            type_: apply_substitution(&substitution, &statement.type_),
         }, substitution);
     }
 
-    fn with_assignment_statement(self: &Self, ctx: &Context, statement: &ast::AssignmentStatement) -> ast::AssignmentStatement {
+    fn with_assignment_statement(self: &Self, ctx: &Context, incoming_substitutions: &SubstitutionMap, statement: &ast::AssignmentStatement) -> (ast::AssignmentStatement, SubstitutionMap) {
+        let (expr, subst) = self.with_expression(ctx, incoming_substitutions, &statement.expression);
+        let mut substitution = compose_substitutions(&incoming_substitutions, &subst);
 
-        return ast::AssignmentStatement{
+        let result_as = ast::AssignmentStatement{
             source: match &statement.source {
                 ast::AssignmentTarget::Variable(variable) => {
-                    let assignment_subs = compose_substitutions(subs, unify(&expr.type_, &variable.type_));
-                    (ast::AssignmentTarget::Variable(ast::VariableUsage{
+                    substitution = compose_substitutions(&substitution, &unify(&variable.type_, &expr.type_));
+                    ast::AssignmentTarget::Variable(ast::VariableUsage{
                         name: variable.name.clone(),
-                        type_: &variable.type_.clone(),
-                    }), assignment_subs)
+                        type_: apply_substitution(&substitution, &variable.type_),
+                    })
                 },
                 ast::AssignmentTarget::StructAttr(struct_attr) => {
-                    // let assignment_subs = compose_substitutions(subs, unify(&expr.type_, &struct_attr.type_));
-                    let (expr, subst) = self.with_expression(ctx, &struct_attr.source);
-
-                    (ast::AssignmentTarget::StructAttr(ast::StructGetter{
-                        source: expr,
+                    let (source, subst) = self.with_expression(ctx, &substitution, &struct_attr.source);
+                    // TODO: match source attr with type
+                    let substitution = compose_substitutions(&compose_substitutions(&substitution, &subst), &unify(&struct_attr.type_, &expr.type_));
+                    ast::AssignmentTarget::StructAttr(ast::StructGetter{
+                        source: source,
                         attribute: struct_attr.attribute.clone(),
-                        type_: &struct_attr.type_.clone(),
-                    }), subst)
+                        type_: apply_substitution(&substitution, &struct_attr.type_),
+                    })
                 },
             },
             expression: expr,
-        }
+        };
+        return (result_as, substitution);
     }
 
-    fn with_expression(self: &Self, ctx: &Context, expression: &ast::Expression) -> (ast::Expression, SubstitutionMap) {
-        let mut substitution = SubstitutionMap::new();
-        let expr = ast::Expression{
-            subexpression: Box::new(match &*expression.subexpression {
-                ast::Subexpression::LiteralInt(literal_int) => {
-                    ast::Subexpression::LiteralInt(ast::LiteralInt{
-                        value: literal_int.value.clone(),
-                        type_: literal_int.type_.clone(),
-                    })
-                },
-                ast::Subexpression::LiteralFloat(literal_float) => {
-                    ast::Subexpression::LiteralFloat(ast::LiteralFloat{
-                        value: literal_float.value.clone(),
-                        type_: literal_float.type_.clone(),
-                    })
-                },
-                ast::Subexpression::LiteralStruct(literal_struct) => {
-                    ast::Subexpression::LiteralStruct(ast::LiteralStruct{
-                        name: literal_struct.name.clone(),
-                        fields: literal_struct.fields.iter().map(|field|{
+    fn with_expression(self: &Self, ctx: &Context, incoming_substitutions: &SubstitutionMap, expression: &ast::Expression) -> (ast::Expression, SubstitutionMap) {
+        let mut substitution = incoming_substitutions.clone();
+        let subexpression = Box::new(match &*expression.subexpression {
+            ast::Subexpression::LiteralInt(literal_int) => {
+                substitution = compose_substitutions(&substitution, &unify(&expression.type_, &literal_int.type_));
+                ast::Subexpression::LiteralInt(ast::LiteralInt{
+                    value: literal_int.value.clone(),
+                    type_: apply_substitution(&substitution, &literal_int.type_),
+                })
+            },
+            ast::Subexpression::LiteralFloat(literal_float) => {
+                substitution = compose_substitutions(&substitution, &unify(&expression.type_, &literal_float.type_));
+                ast::Subexpression::LiteralFloat(ast::LiteralFloat{
+                    value: literal_float.value.clone(),
+                    type_: apply_substitution(&substitution, &literal_float.type_),
+                })
+            },
+            ast::Subexpression::LiteralStruct(literal_struct) => {
+                substitution = compose_substitutions(&substitution, &unify(&expression.type_, &literal_struct.type_));
+                let type_declaration = match &ctx.environment[&literal_struct.name.name.value] {
+                    NamedEntity::TypeDeclaration(ast::TypeDeclaration::Struct(type_declaration)) => {
+                        type_declaration
+                    },
+                    _ => {panic!("literal struct used with non struct name")}
+                };
+                ast::Subexpression::LiteralStruct(ast::LiteralStruct{
+                    name: literal_struct.name.clone(),
+                    fields: literal_struct.fields.iter().map(|field|{
+                        let (result, subst) = self.with_expression(ctx, &substitution, &field.1);
 
-                            // substitution = compose_substitutions(substitution, );
-                            (field.0.clone(), self.with_expression(ctx, &field.1))
-                        }).collect(),
-                        type_: literal_struct.type_.clone(),
-                    })
-                },
-                ast::Subexpression::FunctionCall(function_call) => {
-                    ast::Subexpression::FunctionCall(ast::FunctionCall{
-                        source: self.with_expression(ctx, &function_call.source),
-                        arguments: function_call.arguments.iter().map(|arg| {self.with_expression(ctx, arg)}).collect(),
-                        type_: function_call.type_.clone(),
-                    })
-                },
-                ast::Subexpression::VariableUsage(variable_usage) => {
-                    match ctx.environment[variable_usage.name] {
-                        NamedEntity::TypeDeclaration(_) => {
-                            panic!("Using types not yet supported");
-                        },
-                        NamedEntity::Variable(variable) => {
-                            substitution = compose_substitutions(substitution, unify(variable, expression.type_));
-                        },
-                    }
-                    ast::Subexpression::VariableUsage(ast::VariableUsage{
-                        name: variable_usage.name.clone(),
-                        type_: variable_usage.type_.clone(),
-                    })
-                },
-                ast::Subexpression::StructGetter(struct_getter) => {
-                    ast::Subexpression::StructGetter(ast::StructGetter{
-                        source: self.with_expression(ctx, &struct_getter.source),
-                        attribute: struct_getter.attribute.clone(),
-                        type_: struct_getter.type_.clone(),
-                    })
-                },
-                ast::Subexpression::Block(block) => {
-                    let (result, substitution) = self.with_block(ctx, &block);
-                    substitution = compose_substitutions(substitution, unify(expression.type_, block.type_));
-                    ast::Subexpression::Block(result)
-                },
-                ast::Subexpression::Op(op) => {
-                    let expr_left, subst_left = self.with_expression(ctx, &op.left);
-                    let expr_right, subst_right = self.with_expression(ctx, &op.right);
-                    substitution = compose_substitutions(substitution, subst_left);
-                    substitution = compose_substitutions(substitution, subst_right);
-                    substitution = compose_substitutions(substitution, unify(expression.type_, expr_left.type_));
-                    substitution = compose_substitutions(substitution, unify(expression.type_, expr_right.type_));
-                    ast::Subexpression::Op(ast::Operation{
-                        left: expr_left,
-                        op: op.op.clone(),
-                        right: expr_right,
-                    })
-                },
-            }),
-            type_: expression.type_.clone(),
+                        for type_field in type_declaration.fields.iter() {
+                            if type_field.name.name.value == field.0.name.value {
+                                substitution = compose_substitutions(&substitution, &unify(&type_field.type_, &result.type_));
+                            }
+                        }
+
+                        substitution = compose_substitutions(&substitution, &subst);
+                        (field.0.clone(), result)
+                    }).collect(),
+                    type_: apply_substitution(&substitution, &literal_struct.type_),
+                })
+            },
+            ast::Subexpression::FunctionCall(function_call) => {
+                let (source, subst) = self.with_expression(ctx, &substitution, &function_call.source);
+                substitution = compose_substitutions(&substitution, &subst);
+                match &source.type_ {
+                    ast::TypeUsage::Function(fn_type) => {
+                        substitution = compose_substitutions(&substitution, &unify(&function_call.type_, &*fn_type.return_type));
+                        if function_call.arguments.len() != fn_type.arguments.len() {
+                            panic!("mismatched function argument count");
+                        }
+                    },
+                    ast::TypeUsage::Named(_) => panic!("FunctionCall doesn't have function type."),
+                    _ => {},
+                }
+                substitution = compose_substitutions(&substitution, &unify(&expression.type_, &function_call.type_));
+                ast::Subexpression::FunctionCall(ast::FunctionCall{
+                    source: source.clone(),
+                    arguments: function_call.arguments.iter().enumerate().map(|(i, arg)| {
+                        let (result, subst) = self.with_expression(ctx, &substitution, arg);
+                        substitution = compose_substitutions(&substitution, &subst);
+
+                        match &source.type_ {
+                            ast::TypeUsage::Function(fn_type) => {
+                                substitution = compose_substitutions(&substitution, &unify(&fn_type.arguments[i], &result.type_));
+                            },
+                            ast::TypeUsage::Named(_) => panic!("FunctionCall doesn't have function type."),
+                            _ => {},
+                        }
+                        result
+                    }).collect(),
+                    type_: apply_substitution(&substitution, &function_call.type_),
+                })
+            },
+            ast::Subexpression::VariableUsage(variable_usage) => {
+                match &ctx.environment[&variable_usage.name.name.value] {
+                    NamedEntity::TypeDeclaration(_) => {
+                        panic!("Using types not yet supported");
+                    },
+                    NamedEntity::Variable(variable) => {
+                        substitution = compose_substitutions(&substitution, &unify(&variable_usage.type_, &variable));
+                        substitution = compose_substitutions(&substitution, &unify(&expression.type_, &variable_usage.type_));
+                    },
+                }
+                ast::Subexpression::VariableUsage(ast::VariableUsage{
+                    name: variable_usage.name.clone(),
+                    type_: apply_substitution(&substitution, &variable_usage.type_),
+                })
+            },
+            ast::Subexpression::StructGetter(struct_getter) => {
+                let (source, subst) = self.with_expression(ctx, &substitution, &struct_getter.source);
+                substitution = compose_substitutions(&substitution, &subst);
+
+                match &source.type_ {
+                    ast::TypeUsage::Named(named) => {
+                        match &ctx.environment[&named.name.name.value] {
+                            NamedEntity::TypeDeclaration(ast::TypeDeclaration::Struct(type_declaration)) => {
+                                let mut found = false;
+                                for field in type_declaration.fields.iter() {
+                                    if field.name.name.value == struct_getter.attribute.name.value {
+                                        found = true;
+                                        substitution = compose_substitutions(&substitution, &unify(&struct_getter.type_, &field.type_));
+                                    }
+                                }
+                                if !found {
+                                    println!("foo: {:?} {:?}", &type_declaration.name.name.value, struct_getter.attribute.name.value);
+                                    for method in ctx.impls[&type_declaration.name.name.value].functions.iter() {
+                                        println!("foo: {:?} {:?}", &method.declaration.name.name.value, struct_getter.attribute.name.value);
+                                        if method.declaration.name.name.value == struct_getter.attribute.name.value {
+                                            let mut function_type = ast::FunctionTypeUsage{
+                                                arguments: method.declaration.arguments.iter().map(|arg|{arg.type_.clone()}).collect(),
+                                                return_type: Box::new(method.declaration.return_type.clone()),
+                                            };
+                                            // if the name of the type of the first argument == the class, remove the first arg
+                                            if function_type.arguments.len() > 0 {
+                                                match &function_type.arguments[0] {
+                                                    ast::TypeUsage::Named(named) => {
+                                                        if named.name.name.value == type_declaration.name.name.value {
+                                                            function_type = ast::FunctionTypeUsage{
+                                                                arguments: method.declaration.arguments[1..method.declaration.arguments.len()].iter().map(|arg|{arg.type_.clone()}).collect(),
+                                                                return_type: Box::new(method.declaration.return_type.clone()),
+                                                            };
+                                                        }
+                                                    },
+                                                    _ => {},
+                                                };
+                                            }
+
+                                            println!("found: {:?}", &function_type);
+                                            substitution = compose_substitutions(&substitution, &unify(&struct_getter.type_, &ast::TypeUsage::Function(function_type)));
+                                            found = true;
+                                        }
+                                    }
+                                }
+                                if !found {
+                                    panic!("unknown field name")
+                                }
+
+                            },
+                            _ => panic!("struct getter being used on non-struct")
+                        }
+                    },
+                    ast::TypeUsage::Function(_) => {
+                        panic!("function used with attr")
+                    },
+                    _ => {} // skip unifying if struct type is unknown1
+                }
+
+                substitution = compose_substitutions(&substitution, &unify(&expression.type_, &struct_getter.type_));
+
+                ast::Subexpression::StructGetter(ast::StructGetter{
+                    source: source,
+                    attribute: struct_getter.attribute.clone(),
+                    type_: apply_substitution(&substitution, &struct_getter.type_),
+                })
+            },
+            ast::Subexpression::Block(block) => {
+                let (result, subst) = self.with_block(ctx, &substitution, &block);
+                substitution = compose_substitutions(&substitution, &subst);
+                substitution = compose_substitutions(&substitution, &unify(&expression.type_, &result.type_));
+                println!("foo {:?} {:?}", &expression.type_, &block.type_);
+                ast::Subexpression::Block(result)
+            },
+            ast::Subexpression::Op(op) => {
+                let (expr_left, subst_left) = self.with_expression(ctx, &substitution, &op.left);
+                let (expr_right, subst_right) = self.with_expression(ctx, &substitution, &op.right);
+                substitution = compose_substitutions(&substitution, &subst_left);
+                substitution = compose_substitutions(&substitution, &subst_right);
+                substitution = compose_substitutions(&substitution, &unify(&expression.type_, &expr_left.type_));
+                substitution = compose_substitutions(&substitution, &unify(&expression.type_, &expr_right.type_));
+                ast::Subexpression::Op(ast::Operation{
+                    left: expr_left,
+                    op: op.op.clone(),
+                    right: expr_right,
+                })
+            },
+        });
+
+        let expr = ast::Expression{
+            subexpression: subexpression,
+            type_: apply_substitution(&substitution, &expression.type_),
         };
         return (expr, substitution);
     }