fix parsing

examples/structs.bl

@@ -1,11 +1,7 @@
-fn main(): String {
-  let a = 2;
-  a;
-  a = 3;
-  a = if(true) {"asdf"} else {"fdsa"};
-  a.b.c.d();
-  a = (b + c.d()); // comment
-  return a.b() ;
+fn main(): i64 {
+  let user = User{id: 4};
+  let result = user.instance_method() + User::instance_method(user);
+  return result;
 }
 
 type User struct {
@@ -23,7 +19,7 @@ impl TestTrait for User {
         return Self{id: id};
     }
     fn instance_method(self: Self): i64 {
-        return self.get_id();
+        return self.id;
     }
     fn default_impl(self: Self): i64 {
         return self.instance_method();

goal-examples/webapp/main.bl

@@ -0,0 +1,38 @@
+import net.http as http;
+import logging as logging;
+import json as json;
+
+
+type ExampleResponse struct {
+  pub id: i32;
+  pub name: str;
+  pub email: str;
+}
+
+type Router struct {
+  logger: logging::Logger;
+
+  pub fn new(logger: logging::Logger): Router {
+    return Self{logger: logger};
+  }
+
+  pub fn get_user_data(self: Self, req: http.Request): IO[Result[http::Response, http::Error]] {
+    let response_data = ExampleResponse{
+      id: 4,
+      name: "Andrew",
+      email: "andrew@boringlang.com",
+    };
+    self.logger.info("getting user data")?;
+    return ok(http::Response::ok(json::dumps(response_data)?));
+  }
+}
+
+pub fn main(args: List[String], os: OS): IO[i32] {
+  let logger = logging::ConsoleLogger::new(os.console.stdout());
+  let router = Router::new(logger);
+  let app = http::Router::new("").add_route("/myroute", router.get_user_data);
+  let http_server = http::Server::new(os.net(), "localhost", 8080, app);
+  let err = http_server.serve_forever()?;
+  logger.info("error serving: ", err)?;
+  return 1;
+}

goal-examples/webapp/models.bl

@@ -0,0 +1,33 @@
+import uuid as uuid;
+import orm as orm;
+
+
+#[derive(DeepCopy, Debug, PartialEq, DeriveEntityModel)]
+#[orm::model(table_name = "user")]
+pub type User struct {
+  #[orm::model(primary_key)]
+  pub id: uuid::UUID;
+  #[orm::model(unique, column_type = "VARCHAR(256)")]
+  pub email: String;
+  #[orm::model(nullable)]
+  pub password_hash: Option[String];
+}
+
+#[derive(DeepCopy, Debug, PartialEq, DeriveEntityModel)]
+#[orm::model(table_name = "todo")]
+pub type Todo struct {
+  #[orm::model(primary_key)]
+  pub id: uuid::UUID;
+
+  #[orm::model(foreign_key = "user", on_delete="CASCADE")]
+  pub user_id: uuid::UUID;
+
+  #[orm::model(column_type = "VARCHAR(256)")]
+  pub title: String;
+
+  #[orm::model(column_type = "TEXT")]
+  pub description: String;
+
+  pub created_at: DateTime;
+  pub updated_at: DateTime;
+}

goal-examples/webapp/router.bl

@@ -0,0 +1,45 @@
+import logging as logging;
+import orm as orm;
+import uuid as uuid;
+import webapp.models as models;
+
+#[derive(DeepCopy, Debug, PartialEq)]
+type TodoGetParams struct {
+  #[validate(format="short")]
+  pub id: uuid.UUID;
+}
+
+#[derive(DeepCopy, Debug, PartialEq, Serialize)]
+type TodoResponse struct {
+  #[validate(format="short")]
+  pub id: uuid.UUID;
+  #[validate(format="short")]
+  pub user_id: uuid.UUID;
+  #[validate(min_length=1, max_length=256)]
+  pub title: String;
+  #[validate(min_length=1, max_length=1000000)]
+  pub description: String;
+  pub created_at: DateTime;
+  pub updated_at: DateTime;
+}
+
+impl Into<TodoResponse> for models.Todo {
+  fn into(self: Self): TodoResponse {
+    return TodoResponse{..self};
+  }
+}
+
+type Router struct {
+  logger: logging::Logger;
+  db: orm::DB;
+
+  pub fn new(logger: logging::Logger, db: orm::DB): Router {
+    return Self{logger: logger, db: db};
+  }
+
+  pub fn get_todo(self: Self, req: http.Request[TodoGetParams, http::NoQuery, http::NoBody]): IO[Result[http::JsonResponse[TodoResponse], http::Error]] {
+    let id = req.params.id;
+    let instance = models::Todo::select().filter(models::Todo::Id::equals(id)).first(self.db)??;
+    return http::JsonResponse<TodoResponse>::ok(instance.into());
+  }
+}

packages/boringlang/src/commands/run.ts

@@ -2,6 +2,11 @@ import { defineCommand } from "@bunli/core";
 import { boringGrammar } from "../parse/grammar";
 import { semantics } from "../parse/semantics";
 import TraitChecker from "../types/trait_checker";
+import { TypeAliasResolver } from "../types/type_alias_resolution";
+import { TypeSystem } from "../types/type_system";
+import { TypeChecker } from "../types/type_checker";
+import { TypeResolver } from "../types/type_resolver";
+import { TreeWalkInterpreter } from "../interpreter";
 
 export const run = defineCommand({
   name: "run",
@@ -21,9 +26,29 @@ export const run = defineCommand({
     if (match.succeeded()) {
       const adapter = semantics(match);
       const ast = adapter.toAST();
+      // console.log(JSON.stringify(ast, null, 2));
       new TraitChecker().withModule(ast);
+      const aliasResolvedAst = new TypeAliasResolver().withModule(ast);
+      const typeSystem = new TypeSystem();
+      const typeChecker = new TypeChecker();
+      const typeResolver = new TypeResolver();
 
-      console.log(JSON.stringify(ast, null, 2));
+      typeChecker.withModule(aliasResolvedAst, typeSystem);
+      try {
+        typeSystem.solve();
+      } catch (e) {
+        console.log(e);
+        console.log(JSON.stringify(typeSystem.result, null, 2));
+        return;
+      }
+
+      const typeResolvedAst = typeResolver.withModule(aliasResolvedAst, typeSystem);
+      // console.log(JSON.stringify(typeResolvedAst, null, 2));
+      const interpreter = new TreeWalkInterpreter();
+      const result = interpreter.withModule(typeResolvedAst);
+      console.log(JSON.stringify(result, null, 2));
+
+      // console.log(JSON.stringify(aliasResolvedAst, null, 2));
     } else {
       console.log(match.message);
       // console.log(boringGrammar.trace(text, "Module").toString());

packages/boringlang/src/interpreter/builtins.ts

@@ -0,0 +1,92 @@
+import { Module } from "../parse/ast";
+import { Context, FunctionRef } from "./context";
+
+export function contextFromModule(module: Module): Context {
+  const ctx: Context = {
+    environment: {},
+    currentModule: module,
+  };
+  ctx.environment["i8"] = { namedEntity: "NamedType", isA: "Scalar", fields: {}, impls: [] };
+  ctx.environment["i16"] = { namedEntity: "NamedType", isA: "Scalar", fields: {}, impls: [] };
+  ctx.environment["i32"] = { namedEntity: "NamedType", isA: "Scalar", fields: {}, impls: [] };
+  ctx.environment["i64"] = { namedEntity: "NamedType", isA: "Scalar", fields: {}, impls: [] };
+  ctx.environment["f8"] = { namedEntity: "NamedType", isA: "Scalar", fields: {}, impls: [] };
+  ctx.environment["f16"] = { namedEntity: "NamedType", isA: "Scalar", fields: {}, impls: [] };
+  ctx.environment["f32"] = { namedEntity: "NamedType", isA: "Scalar", fields: {}, impls: [] };
+  ctx.environment["f64"] = { namedEntity: "NamedType", isA: "Scalar", fields: {}, impls: [] };
+  ctx.environment["String"] = { namedEntity: "NamedType", isA: "Scalar", fields: {}, impls: [] };
+  ctx.environment["Void"] = { namedEntity: "NamedType", isA: "Scalar", fields: {}, impls: [] };
+  ctx.environment["Never"] = { namedEntity: "NamedType", isA: "Scalar", fields: {}, impls: [] };
+
+  // add functions, structs, and traits to the context
+  for (const item of module.items) {
+    if (item.moduleItem === "StructTypeDeclaration") {
+      ctx.environment[item.name.text] = {
+        namedEntity: "NamedType",
+        isA: "Struct",
+        fields: Object.fromEntries(item.fields.map((field) => [field.name.text, field.type])),
+        impls: [],
+      };
+    }
+    if (item.moduleItem === "TraitTypeDeclaration") {
+      ctx.environment[item.name.text] = {
+        namedEntity: "NamedType",
+        isA: "Trait",
+        fields: {},
+        impls: [
+          {
+            trait: item.name.text,
+            functions: Object.fromEntries(
+              item.functions.map((fn) => {
+                return [
+                  fn.name,
+                  {
+                    functionType: "UserFunction",
+                    function: fn,
+                  },
+                ];
+              }),
+            ),
+          },
+        ],
+      };
+    }
+    if (item.moduleItem === "Function") {
+      ctx.environment[item.declaration.name.text] = {
+        namedEntity: "Variable",
+        value: {
+          value: "FunctionValue",
+          partial: [],
+          ref: {
+            functionType: "UserFunction",
+            function: item,
+          },
+        },
+      };
+    }
+  }
+  // now that structs and traits are added, add impls
+  for (const item of module.items) {
+    if (item.moduleItem === "Impl") {
+      const struct = ctx.environment[item.struct.name.text];
+      if (!struct || struct.namedEntity !== "NamedType" || struct.isA !== "Struct") {
+        throw Error("Impl for non-struct");
+      }
+      const functions: Record<string, FunctionRef> = {};
+      for (const fn of item.functions) {
+        if (
+          fn.declaration.arguments.length &&
+          fn.declaration.arguments[0].type.typeUsage == "NamedTypeUsage" &&
+          fn.declaration.arguments[0].type.name.text === item.struct.name.text
+        ) {
+          functions[fn.declaration.name.text] = { functionType: "UserFunction", function: fn };
+        }
+      }
+      struct.impls.push({
+        trait: item.trait?.name.text ?? null,
+        functions: functions,
+      });
+    }
+  }
+  return ctx;
+}

packages/boringlang/src/interpreter/context.ts

@@ -0,0 +1,74 @@
+import { TypeUsage, Function, Module } from "../parse/ast";
+
+export interface NumericValue {
+  value: "NumericValue";
+  number: number;
+}
+
+export interface BoolValue {
+  value: "BoolValue";
+  bool: boolean;
+}
+
+export interface StringValue {
+  value: "StringValue";
+  string: string;
+}
+
+export interface UserFunction {
+  functionType: "UserFunction";
+  function: Function;
+}
+
+export interface BuiltinFunction {
+  functionType: "BuiltinFunction";
+  function: (value: Value[]) => Value;
+}
+
+export type FunctionRef = UserFunction | BuiltinFunction;
+
+export interface FunctionValue {
+  value: "FunctionValue";
+  partial: Value[];
+  ref: FunctionRef;
+}
+
+export interface UnitValue {
+  value: "UnitValue";
+}
+
+export interface StructValue {
+  value: "StructValue";
+  source: NamedType;
+  fields: Record<string, Value>;
+}
+
+export type Value =
+  | NumericValue
+  | BoolValue
+  | StringValue
+  | FunctionValue
+  | StructValue
+  | UnitValue;
+
+export interface Variable {
+  namedEntity: "Variable";
+  value: Value;
+}
+
+export interface EnvImpl {
+  trait: string | null;
+  functions: Record<string, FunctionRef>;
+}
+
+export interface NamedType {
+  namedEntity: "NamedType";
+  isA: "Scalar" | "Trait" | "Struct";
+  fields: Record<string, TypeUsage>;
+  impls: EnvImpl[];
+}
+
+export interface Context {
+  environment: Record<string, NamedType | Variable>;
+  currentModule: Module;
+}

packages/boringlang/src/interpreter/index.ts

@@ -0,0 +1,345 @@
+import {
+  AssignmentStatement,
+  Block,
+  Expression,
+  Function,
+  FunctionCall,
+  LetStatement,
+  Module,
+  Operation,
+  Path,
+  ReturnStatement,
+  StructGetter,
+  StructTypeDeclaration,
+  TypeUsage,
+} from "../parse/ast";
+import { contextFromModule } from "./builtins";
+import { Context, NamedType, Value } from "./context";
+
+interface ExpressionResultValue {
+  resultType: "Value";
+  value: Value;
+}
+
+interface ExpressionResultReturn {
+  resultType: "Return";
+  value: Value;
+}
+
+type ExpressionResult = ExpressionResultValue | ExpressionResultReturn;
+
+export class TreeWalkInterpreter {
+  withModule = (module: Module) => {
+    const ctx = contextFromModule(module);
+    const main = ctx.environment["main"];
+    if (
+      !main ||
+      !(main.namedEntity === "Variable") ||
+      !(main.value.value === "FunctionValue") ||
+      !(main.value.ref.functionType === "UserFunction")
+    ) {
+      throw Error("No main function");
+    }
+    return this.withFunction(ctx, main.value.ref.function);
+  };
+
+  withFunction = (ctx: Context, fn: Function): Value => {
+    let result = this.withBlock(ctx, fn.block);
+    return result.value;
+  };
+
+  withBlock = (ctx: Context, block: Block): ExpressionResult => {
+    let last: ExpressionResult = { resultType: "Value", value: { value: "UnitValue" } };
+    for (const statement of block.statements) {
+      if (statement.statementType === "AssignmentStatement") {
+        last = this.withAssignmentStatement(ctx, statement);
+      }
+      if (statement.statementType === "LetStatement") {
+        last = this.withLetStatement(ctx, statement);
+      }
+      if (statement.statementType === "Expression") {
+        last = this.withExpression(ctx, statement);
+      }
+      if (statement.statementType === "ReturnStatement") {
+        last = this.withReturnStatement(ctx, statement);
+      }
+      if (last.resultType === "Return") {
+        return last;
+      }
+    }
+    return last;
+  };
+
+  withAssignmentStatement = (ctx: Context, statement: AssignmentStatement): ExpressionResult => {
+    let result = this.withExpression(ctx, statement.expression);
+    if (result.resultType === "Return") {
+      return result;
+    }
+    if (statement.source.type == "Identifier") {
+      ctx.environment[statement.source.name.text] = {
+        namedEntity: "Variable",
+        value: result.value,
+      };
+    }
+    if (statement.source.type == "StructGetter") {
+      let source = this.withStructGetter(ctx, statement.source.source);
+      if (source.resultType === "Return") {
+        return source;
+      }
+      if (source.value.value !== "StructValue") {
+        throw Error("set attr on nonstruct, should never happen due to type system");
+      }
+      source.value.fields[statement.source.source.attribute.text] = result.value;
+    }
+    return { resultType: "Value", value: { value: "UnitValue" } };
+  };
+
+  withLetStatement = (ctx: Context, statement: LetStatement): ExpressionResult => {
+    let result = this.withExpression(ctx, statement.expression);
+    if (result.resultType === "Return") {
+      return result;
+    }
+    ctx.environment[statement.variableName.text] = {
+      namedEntity: "Variable",
+      value: result.value,
+    };
+    return { resultType: "Value", value: { value: "UnitValue" } };
+  };
+
+  withReturnStatement = (ctx: Context, statement: ReturnStatement): ExpressionResult => {
+    let result = this.withExpression(ctx, statement.source);
+    if (result.resultType === "Return") {
+      return result;
+    }
+    return { resultType: "Return", value: result.value };
+  };
+
+  withExpression = (ctx: Context, expression: Expression): ExpressionResult => {
+    if (expression.subExpression.expressionType === "LiteralInt") {
+      return {
+        resultType: "Value",
+        value: { value: "NumericValue", number: parseInt(expression.subExpression.value) },
+      };
+    }
+    if (expression.subExpression.expressionType === "LiteralFloat") {
+      return {
+        resultType: "Value",
+        value: { value: "NumericValue", number: parseFloat(expression.subExpression.value) },
+      };
+    }
+    if (expression.subExpression.expressionType === "LiteralString") {
+      return {
+        resultType: "Value",
+        value: { value: "StringValue", string: expression.subExpression.value },
+      };
+    }
+    if (expression.subExpression.expressionType === "LiteralBool") {
+      return {
+        resultType: "Value",
+        value: { value: "BoolValue", bool: expression.subExpression.value === "true" },
+      };
+    }
+    if (expression.subExpression.expressionType === "LiteralStruct") {
+      const def = ctx.environment[expression.subExpression.name.text];
+      if (def.namedEntity !== "NamedType") {
+        throw Error("Not a struct");
+      }
+      const fields: Record<string, Value> = {};
+      for (const field of expression.subExpression.fields) {
+        const fieldResult = this.withExpression(ctx, field.expression);
+        if (fieldResult.resultType === "Return") {
+          return fieldResult;
+        }
+        fields[field.name.text] = fieldResult.value;
+      }
+      return {
+        resultType: "Value",
+        value: {
+          value: "StructValue",
+          source: def,
+          fields: fields,
+        },
+      };
+    }
+    if (expression.subExpression.expressionType === "FunctionCall") {
+      return this.withFunctionCall(ctx, expression.subExpression);
+    }
+    if (expression.subExpression.expressionType === "Path") {
+      // const variableValue = ctx.environment[expression.subExpression.name.text];
+      // if (!variableValue || variableValue.namedEntity !== "Variable") {
+      //   throw Error(`not found: ${expression.subExpression.name.text}`);
+      // }
+      const value = this.withPath(ctx, expression.subExpression);
+      return { resultType: "Value", value: value };
+    }
+    if (expression.subExpression.expressionType === "IfExpression") {
+      const condition = this.withExpression(ctx, expression.subExpression.condition);
+      if (condition.resultType === "Return") {
+        return condition;
+      }
+      if (condition.value.value === "BoolValue" && condition.value.bool === true) {
+        return this.withBlock(ctx, expression.subExpression.block);
+      } else {
+        if (expression.subExpression.else) {
+          return this.withBlock(ctx, expression.subExpression.else);
+        } else {
+          return { resultType: "Value", value: { value: "UnitValue" } };
+        }
+      }
+    }
+    if (expression.subExpression.expressionType === "StructGetter") {
+      return this.withStructGetter(ctx, expression.subExpression);
+    }
+    if (expression.subExpression.expressionType === "Block") {
+      return this.withBlock(ctx, expression.subExpression);
+    }
+    if (expression.subExpression.expressionType === "Operation") {
+      return this.withOperation(ctx, expression.subExpression);
+    }
+    // not actually possible, but makes the type system happy
+    return { resultType: "Value", value: { value: "UnitValue" } };
+  };
+
+  withFunctionCall = (ctx: Context, fnCall: FunctionCall): ExpressionResult => {
+    const source = this.withExpression(ctx, fnCall.source);
+    if (source.resultType === "Return") {
+      return source;
+    }
+    const argValues: Value[] = [];
+    for (const arg of fnCall.arguments) {
+      const argValue = this.withExpression(ctx, arg);
+      if (argValue.resultType === "Return") {
+        return argValue;
+      }
+      argValues.push(argValue.value);
+    }
+    if (source.value.value !== "FunctionValue") {
+      throw Error("type error: function call source must be a function");
+    }
+    if (source.value.ref.functionType === "UserFunction") {
+      const fn = source.value.partial;
+      const fnCtx = contextFromModule(ctx.currentModule);
+      let i = 0;
+      for (const arg of source.value.partial) {
+        fnCtx.environment[source.value.ref.function.declaration.arguments[i].name.text] = {
+          namedEntity: "Variable",
+          value: arg,
+        };
+        i = i + 1;
+      }
+      for (const arg of argValues) {
+        fnCtx.environment[source.value.ref.function.declaration.arguments[i].name.text] = {
+          namedEntity: "Variable",
+          value: arg,
+        };
+        i = i + 1;
+      }
+      return { resultType: "Value", value: this.withFunction(fnCtx, source.value.ref.function) };
+    }
+    // builtin
+    let allValues = source.value.partial.concat(argValues);
+    return { resultType: "Value", value: source.value.ref.function(allValues) };
+  };
+
+  withStructGetter = (ctx: Context, structGetter: StructGetter): ExpressionResult => {
+    const source = this.withExpression(ctx, structGetter.source);
+    if (source.resultType === "Return") {
+      return source;
+    }
+    if (source.value.value !== "StructValue") {
+      throw Error("get attr of non-struct");
+    }
+    if (source.value.fields[structGetter.attribute.text]) {
+      return {
+        resultType: "Value",
+        value: source.value.fields[structGetter.attribute.text],
+      };
+    }
+    for (const impl of source.value.source.impls) {
+      for (const [name, method] of Object.entries(impl.functions)) {
+        if (name === structGetter.attribute.text) {
+          return {
+            resultType: "Value",
+            value: { value: "FunctionValue", partial: [source.value], ref: method },
+          };
+        }
+      }
+    }
+    // not actually possible, but makes the type system happy
+    return { resultType: "Value", value: { value: "UnitValue" } };
+  };
+
+  withOperation = (ctx: Context, op: Operation): ExpressionResult => {
+    const left = this.withExpression(ctx, op.left);
+    if (left.resultType === "Return") {
+      return left;
+    }
+    const right = this.withExpression(ctx, op.left);
+    if (right.resultType === "Return") {
+      return right;
+    }
+    if (left.value.value !== "NumericValue" || right.value.value !== "NumericValue") {
+      throw Error("Operation on a Nan");
+    }
+    if (op.op === "+") {
+      return {
+        resultType: "Value",
+        value: { value: "NumericValue", number: left.value.number + right.value.number },
+      };
+    }
+    if (op.op === "-") {
+      return {
+        resultType: "Value",
+        value: { value: "NumericValue", number: left.value.number - right.value.number },
+      };
+    }
+    if (op.op === "*") {
+      return {
+        resultType: "Value",
+        value: { value: "NumericValue", number: left.value.number * right.value.number },
+      };
+    }
+    return {
+      resultType: "Value",
+      value: { value: "NumericValue", number: left.value.number / right.value.number },
+    };
+  };
+
+  withPath = (ctx: Context, path: Path): Value => {
+    if (path.value.type == "Identifier") {
+      const variableValue = ctx.environment[path.value.name.text];
+      if (!variableValue || variableValue.namedEntity !== "Variable") {
+        throw Error(`not found: ${path.value.name.text}`);
+      }
+      return variableValue.value;
+    }
+    if (path.value.type == "Nested") {
+      return this.withPathItem(ctx, path) as Value;
+    }
+    throw Error(`Impossible path`);
+  };
+
+  withPathItem = (ctx: Context, path: Path): NamedType | Value => {
+    if (path.value.type == "Identifier") {
+      const envValue = ctx.environment[path.value.name.text];
+      if (!envValue || envValue.namedEntity !== "NamedType") {
+        throw Error(`not found: ${path.value.name.text}`);
+      }
+      return envValue;
+    }
+    if (path.value.type == "Nested") {
+      const envValue = this.withPathItem(ctx, path.value.parent) as NamedType;
+      if (envValue.isA == "Trait") {
+        throw Error(`Cannot get function impl from raw trait`);
+      }
+      for (const impl of envValue.impls) {
+        for (const [name, method] of Object.entries(impl.functions)) {
+          if (name == path.value.name.text) {
+            return { value: "FunctionValue", partial: [], ref: method };
+          }
+        }
+      }
+    }
+    throw Error(`Impossible path`);
+  };
+}

packages/boringlang/src/parse/ast.ts

@@ -4,7 +4,7 @@ export interface Spanned {
 }
 
 export interface Identifier extends Spanned {
-  name: string;
+  text: string;
 }
 
 export interface LiteralInt {
@@ -57,16 +57,18 @@ export interface StructGetter {
   type: TypeUsage;
 }
 
+export interface Path {
+  expressionType: "Path";
+  value:
+    | { type: "Identifier"; name: Identifier }
+    | { type: "Nested"; parent: Path; name: Identifier };
+}
+
 export interface Operation {
   expressionType: "Operation";
   left: Expression;
   op: "+" | "-" | "*" | "/";
   right: Expression;
-}
-
-export interface VariableUsage {
-  expressionType: "VariableUsage";
-  name: Identifier;
   type: TypeUsage;
 }
 
@@ -87,8 +89,8 @@ export interface Expression {
     | LiteralString
     | LiteralStruct
     | FunctionCall
-    | VariableUsage
     | IfExpression
+    | Path
     | StructGetter
     | Block
     | Operation;
@@ -109,17 +111,14 @@ export interface LetStatement {
 
 export interface AssignmentStatement {
   statementType: "AssignmentStatement";
-  source: VariableUsage | StructGetter;
+  source: { type: "Identifier"; name: Identifier } | { type: "StructGetter"; source: StructGetter };
   expression: Expression;
 }
 
-export type Statement =
-  | ReturnStatement
-  | LetStatement
-  | AssignmentStatement
-  | Expression;
+export type Statement = ReturnStatement | LetStatement | AssignmentStatement | Expression;
 
 export interface Block {
+  expressionType: "Block";
   statements: Statement[];
   type: TypeUsage;
 }
@@ -141,6 +140,14 @@ export interface Function {
   block: Block;
 }
 
+export const functionToType = (fn: FunctionDeclaration): FunctionTypeUsage => {
+  return {
+    typeUsage: "FunctionTypeUsage",
+    arguments: fn.arguments.map((arg) => arg.type),
+    returnType: fn.returnType,
+  };
+};
+
 export interface StructTypeField {
   name: Identifier;
   type: TypeUsage;
@@ -192,3 +199,74 @@ export interface UnknownTypeUsage {
 }
 
 export type TypeUsage = NamedTypeUsage | FunctionTypeUsage | UnknownTypeUsage;
+
+export const newVoid: () => TypeUsage = () => {
+  return {
+    typeUsage: "NamedTypeUsage",
+    name: { text: "Void", spanStart: 0, spanEnd: 0 },
+  };
+};
+
+export const newNever: () => TypeUsage = () => {
+  return {
+    typeUsage: "NamedTypeUsage",
+    name: { text: "Never", spanStart: 0, spanEnd: 0 },
+  };
+};
+
+function containsReturnExpression(expression: Expression) {
+  if (expression.subExpression.expressionType === "LiteralStruct") {
+    for (const field of expression.subExpression.fields) {
+      if (containsReturnExpression(field.expression)) {
+        return true;
+      }
+    }
+  }
+  if (expression.subExpression.expressionType === "IfExpression") {
+    if (containsReturn(expression.subExpression.block)) {
+      return true;
+    }
+    if (expression.subExpression.else && containsReturn(expression.subExpression.else)) {
+      return true;
+    }
+  }
+  if (expression.subExpression.expressionType === "Block") {
+    if (containsReturn(expression.subExpression)) {
+      return true;
+    }
+  }
+  if (expression.subExpression.expressionType === "Operation") {
+    if (containsReturnExpression(expression.subExpression.left)) {
+      return true;
+    }
+    if (containsReturnExpression(expression.subExpression.right)) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+export function containsReturn(block: Block) {
+  for (const statement of block.statements) {
+    if (statement.statementType === "ReturnStatement") {
+      return true;
+    }
+    if (statement.statementType === "AssignmentStatement") {
+      if (containsReturnExpression(statement.expression)) {
+        return true;
+      }
+    }
+    if (statement.statementType === "LetStatement") {
+      if (containsReturnExpression(statement.expression)) {
+        return true;
+      }
+    }
+    if (statement.statementType === "Expression") {
+      if (containsReturnExpression(statement)) {
+        return true;
+      }
+    }
+  }
+  return false;
+}

packages/boringlang/src/parse/grammar.ts

@@ -4,8 +4,8 @@ export const boringGrammar = ohm.grammar(String.raw`
   Boringlang {
     ReturnStatement       = "return" Expression ";"
     LetStatement          = "let" identifier (":" TypeUsage)? "=" Expression ";"
-    AssignmentStatement   = VariableUsage "=" Expression ";"
-                          | StructGetter "=" Expression ";"
+    AssignmentStatement   = identifier "=" Expression ";" -- identifier
+                          | StructGetter "=" Expression ";" -- getter
     ExpressionStatement   = Expression ";"
     Statement             = ExpressionStatement
                           | LetStatement
@@ -19,27 +19,33 @@ export const boringGrammar = ohm.grammar(String.raw`
     LiteralStructField    = identifier ":" Expression
     LiteralStruct         = identifier "{" ListOf<LiteralStructField, ","> "}"
     identifier            = (letter | "_")+(letter | digit | "_")*
-    FunctionCall          = Expression "(" ListOf<Expression, ","> ")"
     StructGetter          = Expression "." identifier
-    VariableUsage         = identifier
     IfExpression          = "if" "(" Expression ")" Block ("else" Block)?
-    Term                  = LiteralInt
+    Path                  = Path "::" identifier -- nested
+                          | identifier -- base
+    PrimaryExpression     = LiteralInt
                           | LiteralFloat
                           | LiteralBool
                           | LiteralString
-                          | LiteralStruct
-                          | IfExpression
-                          | Block
+                          | Path -- path
                           | "(" Expression ")" -- parens
-                          | VariableUsage
-    Factor                = Factor "*" Term -- mult
-                          | Factor "/" Term -- div
-                          | Term
-    Expression            = Expression "+" Factor -- plus
-                          | Expression "-" Factor -- minus
-                          | StructGetter
-                          | FunctionCall
-                          | Factor
+    StructExpression      = LiteralStruct
+                          | Block
+                          | IfExpression
+                          | PrimaryExpression
+    MemberExpression      = MemberExpression "." identifier -- structGetter
+                          | StructExpression
+    CallExpression        = CallExpression "." identifier -- structGetter
+                          | CallExpression "(" ListOf<Expression, ","> ")" -- functionCall
+                          | MemberExpression "(" ListOf<Expression, ","> ")" -- memberFunctionCall
+                          | MemberExpression
+    MultExpression        = MultExpression "*" CallExpression -- mult
+                          | MultExpression "/" CallExpression -- div
+                          | CallExpression
+    AddExpression         = Expression "+" MultExpression -- plus
+                          | Expression "-" MultExpression -- minus
+                          | MultExpression 
+    Expression            = AddExpression
     Block                 = "{" Statement* Expression? "}"
     NamedTypeUsage        = identifier
     TypeUsage             = NamedTypeUsage

packages/boringlang/src/parse/semantics.ts

@@ -1,6 +1,7 @@
 import {
   AssignmentStatement,
   Block,
+  containsReturn,
   Expression,
   Function,
   FunctionArgument,
@@ -19,7 +20,9 @@ import {
   Module,
   ModuleItem,
   NamedTypeUsage,
+  newNever,
   Operation,
+  Path,
   ReturnStatement,
   Statement,
   StructField,
@@ -29,7 +32,6 @@ import {
   TraitTypeDeclaration,
   TypeDeclaration,
   TypeUsage,
-  VariableUsage,
 } from "./ast";
 import { boringGrammar } from "./grammar";
 
@@ -42,46 +44,60 @@ function nextUnknown() {
 
 export const semantics = boringGrammar.createSemantics();
 semantics.addOperation<any>("toAST", {
-  LiteralInt(a): LiteralInt {
-    console.log(this);
-    console.log(a.source.startIdx);
+  LiteralInt(a): Expression {
     return {
-      expressionType: "LiteralInt",
-      value: this.sourceString,
-      type: {
-        typeUsage: "NamedTypeUsage",
-        name: { name: "i64", spanStart: 0, spanEnd: 0 },
+      statementType: "Expression",
+      subExpression: {
+        expressionType: "LiteralInt",
+        value: this.sourceString,
+        type: {
+          typeUsage: "NamedTypeUsage",
+          name: { text: "i64", spanStart: 0, spanEnd: 0 },
+        },
       },
+      type: { typeUsage: "UnknownTypeUsage", name: nextUnknown() },
     };
   },
-  LiteralFloat(_1, _2, _3): LiteralFloat {
+  LiteralFloat(_1, _2, _3): Expression {
     return {
-      expressionType: "LiteralFloat",
-      value: this.sourceString,
-      type: {
-        typeUsage: "NamedTypeUsage",
-        name: { name: "f64", spanStart: 0, spanEnd: 0 },
+      statementType: "Expression",
+      subExpression: {
+        expressionType: "LiteralFloat",
+        value: this.sourceString,
+        type: {
+          typeUsage: "NamedTypeUsage",
+          name: { text: "f64", spanStart: 0, spanEnd: 0 },
+        },
       },
+      type: { typeUsage: "UnknownTypeUsage", name: nextUnknown() },
     };
   },
-  LiteralBool(_): LiteralBool {
+  LiteralBool(_): Expression {
     return {
-      expressionType: "LiteralBool",
-      value: this.sourceString,
-      type: {
-        typeUsage: "NamedTypeUsage",
-        name: { name: "bool", spanStart: 0, spanEnd: 0 },
+      statementType: "Expression",
+      subExpression: {
+        expressionType: "LiteralBool",
+        value: this.sourceString,
+        type: {
+          typeUsage: "NamedTypeUsage",
+          name: { text: "bool", spanStart: 0, spanEnd: 0 },
+        },
       },
+      type: { typeUsage: "UnknownTypeUsage", name: nextUnknown() },
     };
   },
-  LiteralString(_1, text, _3): LiteralString {
+  LiteralString(_1, text, _3): Expression {
     return {
-      expressionType: "LiteralString",
-      value: text.sourceString,
-      type: {
-        typeUsage: "NamedTypeUsage",
-        name: { name: "String", spanStart: 0, spanEnd: 0 },
+      statementType: "Expression",
+      subExpression: {
+        expressionType: "LiteralString",
+        value: text.sourceString,
+        type: {
+          typeUsage: "NamedTypeUsage",
+          name: { text: "String", spanStart: 0, spanEnd: 0 },
+        },
       },
+      type: { typeUsage: "UnknownTypeUsage", name: nextUnknown() },
     };
   },
   LiteralStructField(identifier, _2, expression): StructField {
@@ -90,98 +106,202 @@ semantics.addOperation<any>("toAST", {
       expression: expression.toAST(),
     };
   },
-  LiteralStruct(identifier, _2, fields, _4): LiteralStruct {
+  LiteralStruct(identifier, _2, fields, _4): Expression {
     return {
-      expressionType: "LiteralStruct",
-      name: identifier.toAST(),
-      fields: fields.asIteration().children.map((c) => c.toAST()),
-      type: { typeUsage: "NamedTypeUsage", name: identifier.toAST() },
+      statementType: "Expression",
+      subExpression: {
+        expressionType: "LiteralStruct",
+        name: identifier.toAST(),
+        fields: fields.asIteration().children.map((c) => c.toAST()),
+        type: { typeUsage: "NamedTypeUsage", name: identifier.toAST() },
+      },
+      type: { typeUsage: "UnknownTypeUsage", name: nextUnknown() },
     };
   },
   identifier(_1, _2): Identifier {
     return {
-      name: this.sourceString,
+      text: this.sourceString,
       spanStart: this.source.startIdx,
       spanEnd: this.source.endIdx,
     };
   },
-  FunctionCall(expression, _2, args, _4): FunctionCall {
+  PrimaryExpression(literal): Expression {
+    return literal.toAST();
+  },
+  PrimaryExpression_path(path): Expression {
     return {
-      expressionType: "FunctionCall",
-      source: expression.toAST(),
-      arguments: args.asIteration().children.map((c) => c.toAST()),
+      statementType: "Expression",
+      subExpression: path.toAST(),
       type: { typeUsage: "UnknownTypeUsage", name: nextUnknown() },
     };
   },
-  StructGetter(expression, _2, identifier): StructGetter {
+  PrimaryExpression_parens(_1, term, _3): Expression {
+    return term.toAST();
+  },
+  StructExpression(expression): Expression {
+    return expression.toAST();
+  },
+  MemberExpression(expression): Expression {
+    return expression.toAST();
+  },
+  MemberExpression_structGetter(expression, _2, identifier): Expression {
     return {
-      expressionType: "StructGetter",
-      source: expression.toAST(),
-      attribute: identifier.toAST(),
+      statementType: "Expression",
+      subExpression: {
+        expressionType: "StructGetter",
+        source: expression.toAST(),
+        attribute: identifier.toAST(),
+        type: { typeUsage: "UnknownTypeUsage", name: nextUnknown() },
+      },
       type: { typeUsage: "UnknownTypeUsage", name: nextUnknown() },
     };
   },
-  VariableUsage(identifier): VariableUsage {
+  CallExpression(expression): Expression {
+    return expression.toAST();
+  },
+  CallExpression_structGetter(expression, _2, identifier): Expression {
     return {
-      expressionType: "VariableUsage",
-      name: identifier.toAST(),
+      statementType: "Expression",
+      subExpression: {
+        expressionType: "StructGetter",
+        source: expression.toAST(),
+        attribute: identifier.toAST(),
+        type: { typeUsage: "UnknownTypeUsage", name: nextUnknown() },
+      },
       type: { typeUsage: "UnknownTypeUsage", name: nextUnknown() },
     };
   },
-  IfExpression(_1, _2, expression, _4, block, _6, elseBlock): IfExpression {
+  CallExpression_functionCall(expression, _2, args, _4): Expression {
+    const resolvedArgs = args.asIteration().children.map((c) => c.toAST());
+    return {
+      statementType: "Expression",
+      subExpression: {
+        expressionType: "FunctionCall",
+        source: expression.toAST(),
+        arguments: resolvedArgs,
+        type: {
+          typeUsage: "UnknownTypeUsage",
+          name: nextUnknown(),
+        },
+      },
+      type: { typeUsage: "UnknownTypeUsage", name: nextUnknown() },
+    };
+  },
+  CallExpression_memberFunctionCall(expression, _2, args, _4): Expression {
+    const resolvedArgs = args.asIteration().children.map((c) => c.toAST());
+    return {
+      statementType: "Expression",
+      subExpression: {
+        expressionType: "FunctionCall",
+        source: expression.toAST(),
+        arguments: resolvedArgs,
+        type: {
+          typeUsage: "UnknownTypeUsage",
+          name: nextUnknown(),
+        },
+      },
+      type: { typeUsage: "UnknownTypeUsage", name: nextUnknown() },
+    };
+  },
+  StructGetter(expression, _2, identifier): Expression {
+    return {
+      statementType: "Expression",
+      subExpression: {
+        expressionType: "StructGetter",
+        source: expression.toAST(),
+        attribute: identifier.toAST(),
+        type: { typeUsage: "UnknownTypeUsage", name: nextUnknown() },
+      },
+      type: { typeUsage: "UnknownTypeUsage", name: nextUnknown() },
+    };
+  },
+  IfExpression(_1, _2, expression, _4, block, _6, elseBlock): Expression {
     const eb = elseBlock.toAST();
     return {
-      expressionType: "IfExpression",
-      condition: expression.toAST(),
-      block: block.toAST(),
-      else: eb.length > 0 ? eb[0] : null,
+      statementType: "Expression",
+      subExpression: {
+        expressionType: "IfExpression",
+        condition: expression.toAST(),
+        block: block.toAST(),
+        else: eb.length > 0 ? eb[0] : null,
+        type: { typeUsage: "UnknownTypeUsage", name: nextUnknown() },
+      },
       type: { typeUsage: "UnknownTypeUsage", name: nextUnknown() },
     };
   },
-  Term(term): Expression {
-    return term.toAST();
+  Path_base(identifier): Path {
+    return {
+      expressionType: "Path",
+      value: { type: "Identifier", name: identifier.toAST() },
+    };
   },
-  Term_parens(_1, term, _3): Expression {
-    return term.toAST();
+  Path_nested(basePath, _2, attrIdent): Path {
+    return {
+      expressionType: "Path",
+      value: { type: "Nested", parent: basePath.toAST(), name: attrIdent.toAST() },
+    };
   },
-  Factor(factor): Expression {
-    return factor.toAST();
+  MultExpression(expression): Expression {
+    return expression.toAST();
+  },
+  MultExpression_mult(factor, _2, term): Expression {
+    return {
+      statementType: "Expression",
+      subExpression: {
+        expressionType: "Operation",
+        left: factor.toAST(),
+        op: "*",
+        right: term.toAST(),
+        type: { typeUsage: "UnknownTypeUsage", name: nextUnknown() },
+      },
+      type: { typeUsage: "UnknownTypeUsage", name: nextUnknown() },
+    };
+  },
+  MultExpression_div(factor, _2, term): Expression {
+    return {
+      statementType: "Expression",
+      subExpression: {
+        expressionType: "Operation",
+        left: factor.toAST(),
+        op: "/",
+        right: term.toAST(),
+        type: { typeUsage: "UnknownTypeUsage", name: nextUnknown() },
+      },
+      type: { typeUsage: "UnknownTypeUsage", name: nextUnknown() },
+    };
+  },
+  AddExpression(expression): Expression {
+    return expression.toAST();
+  },
+  AddExpression_plus(expression, _2, factor): Expression {
+    return {
+      statementType: "Expression",
+      subExpression: {
+        expressionType: "Operation",
+        left: expression.toAST(),
+        op: "+",
+        right: factor.toAST(),
+        type: { typeUsage: "UnknownTypeUsage", name: nextUnknown() },
+      },
+      type: { typeUsage: "UnknownTypeUsage", name: nextUnknown() },
+    };
+  },
+  AddExpression_minus(expression, _2, factor): Expression {
+    return {
+      statementType: "Expression",
+      subExpression: {
+        expressionType: "Operation",
+        left: expression.toAST(),
+        op: "-",
+        right: factor.toAST(),
+        type: { typeUsage: "UnknownTypeUsage", name: nextUnknown() },
+      },
+      type: { typeUsage: "UnknownTypeUsage", name: nextUnknown() },
+    };
   },
   Expression(expression): Expression {
     return expression.toAST();
   },
-  Expression_plus(expression, _2, factor): Operation {
-    return {
-      expressionType: "Operation",
-      left: expression.toAST(),
-      op: "+",
-      right: factor.toAST(),
-    };
-  },
-  Expression_minus(expression, _2, factor): Operation {
-    return {
-      expressionType: "Operation",
-      left: expression.toAST(),
-      op: "-",
-      right: factor.toAST(),
-    };
-  },
-  Factor_mult(factor, _2, term): Operation {
-    return {
-      expressionType: "Operation",
-      left: factor.toAST(),
-      op: "*",
-      right: term.toAST(),
-    };
-  },
-  Factor_div(factor, _2, term): Operation {
-    return {
-      expressionType: "Operation",
-      left: factor.toAST(),
-      op: "/",
-      right: term.toAST(),
-    };
-  },
   Statement(statement): Statement {
     return statement.toAST();
   },
@@ -197,16 +317,20 @@ semantics.addOperation<any>("toAST", {
       statementType: "LetStatement",
       variableName: ident.toAST(),
       expression: expression.toAST(),
-      type:
-        tu.length > 0
-          ? tu[0]
-          : { typeUsage: "UnknownTypeUsage", name: nextUnknown() },
+      type: tu.length > 0 ? tu[0] : { typeUsage: "UnknownTypeUsage", name: nextUnknown() },
     };
   },
-  AssignmentStatement(variable, _2, expression, _4): AssignmentStatement {
+  AssignmentStatement_identifier(variable, _2, expression, _4): AssignmentStatement {
     return {
       statementType: "AssignmentStatement",
-      source: variable.toAST(),
+      source: { type: "Identifier", name: variable.toAST() },
+      expression: expression.toAST(),
+    };
+  },
+  AssignmentStatement_getter(variable, _2, expression, _4): AssignmentStatement {
+    return {
+      statementType: "AssignmentStatement",
+      source: { type: "StructGetter", source: variable.toAST() },
       expression: expression.toAST(),
     };
   },
@@ -220,11 +344,18 @@ semantics.addOperation<any>("toAST", {
   Block(_1, statements, expression, _4): Block {
     const lines = statements.asIteration().children.map((c) => c.toAST());
     const finalExpression = expression.toAST();
-    lines.push(finalExpression.length > 0 ? finalExpression[0] : null);
-    return {
+    if (finalExpression.length > 0) {
+      lines.push(finalExpression[0]);
+    }
+    const block: Block = {
+      expressionType: "Block",
       statements: lines,
-      type: { typeUsage: "UnknownTypeUsage", name: nextUnknown() },
+      type: newNever(),
     };
+    if (!containsReturn(block)) {
+      block.type = { typeUsage: "UnknownTypeUsage", name: nextUnknown() };
+    }
+    return block;
   },
   NamedTypeUsage(name): NamedTypeUsage {
     return {
@@ -248,15 +379,7 @@ semantics.addOperation<any>("toAST", {
       type: typeUsage.toAST(),
     };
   },
-  FunctionDeclaration(
-    _1,
-    identifier,
-    _3,
-    args,
-    _4,
-    _5,
-    returnType,
-  ): FunctionDeclaration {
+  FunctionDeclaration(_1, identifier, _3, args, _4, _5, returnType): FunctionDeclaration {
     return {
       name: identifier.toAST(),
       arguments: args.asIteration().children.map((c) => c.toAST()),
@@ -276,14 +399,7 @@ semantics.addOperation<any>("toAST", {
       type: typeUsage.toAST(),
     };
   },
-  StructTypeDeclaration(
-    _1,
-    identifier,
-    _3,
-    _4,
-    fields,
-    _6,
-  ): StructTypeDeclaration {
+  StructTypeDeclaration(_1, identifier, _3, _4, fields, _6): StructTypeDeclaration {
     return {
       moduleItem: "StructTypeDeclaration",
       typeDeclaration: "StructTypeDeclaration",
@@ -294,14 +410,7 @@ semantics.addOperation<any>("toAST", {
   TraitMethod(declaration, _2): FunctionDeclaration {
     return declaration.toAST();
   },
-  TraitTypeDeclaration(
-    _1,
-    identifier,
-    _3,
-    _4,
-    methods,
-    _5,
-  ): TraitTypeDeclaration {
+  TraitTypeDeclaration(_1, identifier, _3, _4, methods, _5): TraitTypeDeclaration {
     return {
       moduleItem: "TraitTypeDeclaration",
       typeDeclaration: "TraitTypeDeclaration",

packages/boringlang/src/types/builtins.ts

@@ -0,0 +1,21 @@
+import { Context } from "./context";
+
+export function newContext(): Context {
+  const result: Context = {
+    currentFunctionReturn: null,
+    environment: {},
+  };
+  result.environment["i8"] = { namedEntity: "NamedType", isA: "Scalar", fields: {}, impls: [] };
+  result.environment["i16"] = { namedEntity: "NamedType", isA: "Scalar", fields: {}, impls: [] };
+  result.environment["i32"] = { namedEntity: "NamedType", isA: "Scalar", fields: {}, impls: [] };
+  result.environment["i64"] = { namedEntity: "NamedType", isA: "Scalar", fields: {}, impls: [] };
+  result.environment["f8"] = { namedEntity: "NamedType", isA: "Scalar", fields: {}, impls: [] };
+  result.environment["f16"] = { namedEntity: "NamedType", isA: "Scalar", fields: {}, impls: [] };
+  result.environment["f32"] = { namedEntity: "NamedType", isA: "Scalar", fields: {}, impls: [] };
+  result.environment["f64"] = { namedEntity: "NamedType", isA: "Scalar", fields: {}, impls: [] };
+  result.environment["String"] = { namedEntity: "NamedType", isA: "Scalar", fields: {}, impls: [] };
+  result.environment["Void"] = { namedEntity: "NamedType", isA: "Scalar", fields: {}, impls: [] };
+  result.environment["Never"] = { namedEntity: "NamedType", isA: "Scalar", fields: {}, impls: [] };
+
+  return result;
+}

packages/boringlang/src/types/context.ts

@@ -0,0 +1,95 @@
+import { FunctionTypeUsage, NamedTypeUsage, TypeUsage } from "../parse/ast";
+
+interface EnvImpl {
+  trait: string | null;
+  functions: Record<string, FunctionTypeUsage>;
+}
+
+interface NamedType {
+  namedEntity: "NamedType";
+  isA: "Scalar" | "Trait" | "Struct";
+  fields: Record<string, TypeUsage>;
+  impls: EnvImpl[];
+}
+
+interface Variable {
+  namedEntity: "Variable";
+  type: TypeUsage;
+}
+
+type NamedEntity = NamedType | Variable;
+
+export interface Context {
+  currentFunctionReturn: TypeUsage | null;
+  environment: Record<string, NamedEntity>;
+}
+
+export function getAttr(ctx: Context, name: string, field: string) {
+  const struct = ctx.environment[name];
+  if (!struct || struct.namedEntity !== "NamedType") {
+    throw Error(`Unknown type ${name}`);
+  }
+  if (struct.fields[field]) {
+    return struct.fields[field];
+  }
+  let results: TypeUsage[] = [];
+  for (const impl of struct.impls) {
+    if (impl.functions[field]) {
+      const fn = impl.functions[field];
+
+      if (
+        fn.arguments.length &&
+        fn.arguments[0].typeUsage == "NamedTypeUsage" &&
+        fn.arguments[0].name.text === name
+      ) {
+        const fnCopy = deepCopy(fn);
+        fnCopy.arguments = fnCopy.arguments.slice(1);
+        results.push(fnCopy);
+      }
+    }
+  }
+  if (results.length === 0) {
+    throw Error(`${name} has no attribue ${field}`);
+  }
+  if (results.length > 1) {
+    throw Error(`${name} has multiple attribues ${field}, use universal function call syntax`);
+  }
+  return results[0];
+}
+
+export function typeExists(ctx: Context, type: TypeUsage) {
+  if (type.typeUsage === "NamedTypeUsage") {
+    if (
+      !ctx.environment[type.name.text] ||
+      ctx.environment[type.name.text].namedEntity !== "NamedType"
+    ) {
+      throw Error(`${type.name.text} is not a type.`);
+    }
+  }
+  if (type.typeUsage === "FunctionTypeUsage") {
+    for (const arg of type.arguments) {
+      typeExists(ctx, arg);
+    }
+    typeExists(ctx, type.returnType);
+  }
+}
+
+export function replaceType(oldName: string, newType: TypeUsage, inType: TypeUsage) {
+  if (inType.typeUsage === "NamedTypeUsage") {
+    if (inType.name.text === oldName) {
+      return deepCopy(newType);
+    }
+  }
+  if (inType.typeUsage === "FunctionTypeUsage") {
+    const result = deepCopy(inType);
+    for (const [i, arg] of inType.arguments.entries()) {
+      result.arguments[i] = replaceType(oldName, newType, arg);
+    }
+    result.returnType = replaceType(oldName, newType, inType.returnType);
+  }
+  return deepCopy(inType);
+}
+
+export const deepCopy = <T>(o: T) => {
+  return JSON.parse(JSON.stringify(o)) as T;
+};

packages/boringlang/src/types/trait_checker.ts

@@ -1,35 +1,16 @@
 import { Impl, Module, TraitTypeDeclaration, TypeUsage } from "../parse/ast";
+import { compareTypes } from "./type_system";
 
 interface Context {
   environment: Record<string, TraitTypeDeclaration>;
 }
 
-const compareTypes = (typeA: TypeUsage, typeB: TypeUsage) => {
-  if (typeA.typeUsage !== typeB.typeUsage) {
-    throw Error(`Mismatched types: ${typeA.typeUsage} ${typeB.typeUsage}`);
-  }
-  if (typeA.typeUsage == "NamedTypeUsage" && typeB.typeUsage == "NamedTypeUsage") {
-    if (typeA.name.name !== typeB.name.name) {
-      throw Error(`Mismatched types: ${typeA.name.name} ${typeB.name.name}`);
-    }
-  }
-  if (typeA.typeUsage == "FunctionTypeUsage" && typeB.typeUsage == "FunctionTypeUsage") {
-    if (typeA.arguments.length !== typeB.arguments.length) {
-      throw Error(`Mismatched arg lengths: ${typeA.arguments.length} ${typeB.arguments.length}`);
-    }
-    for (let i = 0; i < typeA.arguments.length; i++) {
-      compareTypes(typeA.arguments[i], typeB.arguments[i]);
-    }
-    compareTypes(typeA.returnType, typeB.returnType);
-  }
-};
-
 export default class TraitChecker {
   withModule = (module: Module) => {
     let ctx: Context = { environment: {} };
     for (const item of module.items) {
       if (item.moduleItem == "TraitTypeDeclaration") {
-        ctx.environment[item.name.name] = item;
+        ctx.environment[item.name.text] = item;
       }
     }
     for (const item of module.items) {
@@ -38,22 +19,33 @@ export default class TraitChecker {
       }
     }
   };
+  withTrait = (trait: TraitTypeDeclaration) => {
+    for (const fn of trait.functions) {
+      if (fn.arguments.length === 0) {
+        throw new Error("First argument of trait method must be Self");
+      }
+      const firstArg = fn.arguments[0];
+      if (firstArg.type.typeUsage !== "NamedTypeUsage" || firstArg.type.name.text !== "Self") {
+        throw new Error("First argument of trait method must be Self");
+      }
+    }
+  };
   withImpl = (ctx: Context, impl: Impl) => {
     if (new Set(impl.functions.map((fn) => fn.declaration.name)).size !== impl.functions.length) {
-      throw Error(`Duplicate functions in ${impl.struct.name.name}`);
+      throw Error(`Duplicate functions in ${impl.struct.name.text}`);
     }
     if (impl.trait == null) {
       return;
     }
-    const trait = ctx.environment[impl.trait.name.name];
+    const trait = ctx.environment[impl.trait.name.text];
     if (!trait) {
       throw Error(`No such trait: ${impl.trait.name}`);
     }
     if (impl.functions.length !== trait.functions.length) {
-      throw Error(`Mismatched impl/trait len ${impl.trait.name.name} for ${impl.struct.name.name}`);
+      throw Error(`Mismatched impl/trait len ${impl.trait.name.text} for ${impl.struct.name.text}`);
     }
     for (let i = 0; i < impl.functions.length; i++) {
-      if (impl.functions[i].declaration.name.name !== trait.functions[i].name.name) {
+      if (impl.functions[i].declaration.name.text !== trait.functions[i].name.text) {
         throw Error(
           `Mismatched impl/trait names ${impl.functions[i].declaration.name} for ${trait.functions[i].name}`,
         );

packages/boringlang/src/types/type_alias_resolution.ts

@@ -0,0 +1,233 @@
+import {
+  AssignmentStatement,
+  Block,
+  Expression,
+  Function,
+  FunctionCall,
+  FunctionDeclaration,
+  IfExpression,
+  Impl,
+  LetStatement,
+  LiteralStruct,
+  Module,
+  Operation,
+  ReturnStatement,
+  StructGetter,
+  StructTypeDeclaration,
+  TraitTypeDeclaration,
+  TypeUsage,
+  Path,
+} from "../parse/ast";
+import { deepCopy, replaceType } from "./context";
+
+interface AliasContext {
+  environment: Record<string, TypeUsage>;
+}
+
+export class TypeAliasResolver {
+  withModule = (module: Module) => {
+    const ctx: AliasContext = { environment: {} };
+
+    const result = deepCopy(module);
+    for (const [i, item] of module.items.entries()) {
+      if (item.moduleItem === "TraitTypeDeclaration") {
+        let traitCtx = deepCopy(ctx);
+        traitCtx.environment["Self"] = { typeUsage: "NamedTypeUsage", name: item.name };
+        result.items[i] = this.withTraitTypeDeclaration(traitCtx, item);
+      }
+      if (item.moduleItem === "Impl") {
+        let implCtx = deepCopy(ctx);
+        implCtx.environment["Self"] = { typeUsage: "NamedTypeUsage", name: item.struct.name };
+        result.items[i] = this.withImpl(implCtx, item);
+      }
+      if (item.moduleItem === "StructTypeDeclaration") {
+        let structCtx = deepCopy(ctx);
+        structCtx.environment["Self"] = { typeUsage: "NamedTypeUsage", name: item.name };
+        result.items[i] = this.withStructDeclaration(structCtx, item);
+      }
+    }
+    return result;
+  };
+
+  withTraitTypeDeclaration = (ctx: AliasContext, trait: TraitTypeDeclaration) => {
+    const result = deepCopy(trait);
+    for (const [oldName, newType] of Object.entries(ctx.environment)) {
+      for (const [i, fn] of trait.functions.entries()) {
+        result.functions[i] = this.withFunctionDeclaration(ctx, fn);
+      }
+    }
+    return result;
+  };
+
+  withImpl = (ctx: AliasContext, impl: Impl) => {
+    const result = deepCopy(impl);
+    for (const [oldName, newType] of Object.entries(ctx.environment)) {
+      for (const [i, fn] of impl.functions.entries()) {
+        result.functions[i] = this.withFunction(ctx, fn);
+      }
+    }
+    return result;
+  };
+
+  withStructDeclaration = (ctx: AliasContext, struct: StructTypeDeclaration) => {
+    const result = deepCopy(struct);
+    for (const [oldName, newType] of Object.entries(ctx.environment)) {
+      for (const [i, field] of struct.fields.entries()) {
+        result.fields[i].type = replaceType(oldName, newType, field.type);
+      }
+    }
+    return result;
+  };
+
+  withFunctionDeclaration = (ctx: AliasContext, fn: FunctionDeclaration) => {
+    const result = deepCopy(fn);
+    for (const [oldName, newType] of Object.entries(ctx.environment)) {
+      for (const [i, arg] of fn.arguments.entries()) {
+        result.arguments[i].type = replaceType(oldName, newType, arg.type);
+      }
+      result.returnType = replaceType(oldName, newType, result.returnType);
+    }
+    return result;
+  };
+
+  withFunction = (ctx: AliasContext, fn: Function) => {
+    const result = deepCopy(fn);
+    result.declaration = this.withFunctionDeclaration(ctx, fn.declaration);
+    result.block = this.withBlock(ctx, fn.block);
+    return result;
+  };
+
+  withBlock = (ctx: AliasContext, block: Block) => {
+    const result = deepCopy(block);
+    for (const [i, statement] of block.statements.entries()) {
+      if (statement.statementType === "AssignmentStatement") {
+        result.statements[i] = this.withAssignmentStatement(ctx, statement);
+      }
+      if (statement.statementType === "LetStatement") {
+        result.statements[i] = this.withLetStatement(ctx, statement);
+      }
+      if (statement.statementType === "Expression") {
+        result.statements[i] = this.withExpression(ctx, statement);
+      }
+      if (statement.statementType === "ReturnStatement") {
+        result.statements[i] = this.withReturnStatement(ctx, statement);
+      }
+      for (const [oldName, newType] of Object.entries(ctx.environment)) {
+        result.type = replaceType(oldName, newType, block.type);
+      }
+    }
+    return result;
+  };
+
+  withAssignmentStatement = (ctx: AliasContext, statement: AssignmentStatement) => {
+    const result = deepCopy(statement);
+    if (statement.source.type == "StructGetter") {
+      result.source = {
+        type: "StructGetter",
+        source: this.withStructGetter(ctx, statement.source.source),
+      };
+    }
+    if (statement.source.type == "Identifier") {
+      result.source = deepCopy(result.source);
+    }
+    result.expression = this.withExpression(ctx, statement.expression);
+    return result;
+  };
+
+  withLetStatement = (ctx: AliasContext, statement: LetStatement) => {
+    const result = deepCopy(statement);
+    result.expression = this.withExpression(ctx, statement.expression);
+    return result;
+  };
+
+  withReturnStatement = (ctx: AliasContext, statement: ReturnStatement) => {
+    const result = deepCopy(statement);
+    result.source = this.withExpression(ctx, statement.source);
+    return result;
+  };
+
+  withExpression = (ctx: AliasContext, expression: Expression) => {
+    const result = deepCopy(expression);
+    if (expression.subExpression.expressionType === "LiteralStruct") {
+      result.subExpression = this.withLiteralStruct(ctx, expression.subExpression);
+    }
+    if (expression.subExpression.expressionType === "FunctionCall") {
+      result.subExpression = this.withFunctionCall(ctx, expression.subExpression);
+    }
+    if (expression.subExpression.expressionType === "Path") {
+      result.subExpression = deepCopy(expression.subExpression);
+    }
+    if (expression.subExpression.expressionType === "IfExpression") {
+      result.subExpression = this.withIfExpression(ctx, expression.subExpression);
+    }
+    if (expression.subExpression.expressionType === "StructGetter") {
+      result.subExpression = this.withStructGetter(ctx, expression.subExpression);
+    }
+    if (expression.subExpression.expressionType === "Block") {
+      result.subExpression = this.withBlock(ctx, expression.subExpression);
+    }
+    if (expression.subExpression.expressionType === "Operation") {
+      result.subExpression = this.withOperation(ctx, expression.subExpression);
+    }
+    return result;
+  };
+
+  withLiteralStruct = (ctx: AliasContext, literalStruct: LiteralStruct) => {
+    const result = deepCopy(literalStruct);
+    for (const [i, field] of literalStruct.fields.entries()) {
+      result.fields[i].expression = this.withExpression(ctx, field.expression);
+    }
+
+    for (const [oldName, newType] of Object.entries(ctx.environment)) {
+      result.type = replaceType(oldName, newType, literalStruct.type);
+      if (result.name.text === oldName && newType.typeUsage === "NamedTypeUsage") {
+        result.name = newType.name;
+      }
+    }
+    return result;
+  };
+
+  withFunctionCall = (ctx: AliasContext, fnCall: FunctionCall) => {
+    const result = deepCopy(fnCall);
+    for (const [i, arg] of fnCall.arguments.entries()) {
+      result.arguments[i] = this.withExpression(ctx, arg);
+    }
+    result.source = this.withExpression(ctx, fnCall.source);
+    for (const [oldName, newType] of Object.entries(ctx.environment)) {
+      result.type = replaceType(oldName, newType, fnCall.type);
+    }
+    return result;
+  };
+
+  withIfExpression = (ctx: AliasContext, ifExpression: IfExpression) => {
+    const result = deepCopy(ifExpression);
+    result.condition = this.withExpression(ctx, ifExpression.condition);
+    result.block = this.withBlock(ctx, ifExpression.block);
+    if (ifExpression.else) {
+      result.else = this.withBlock(ctx, ifExpression.else);
+    }
+    for (const [oldName, newType] of Object.entries(ctx.environment)) {
+      result.type = replaceType(oldName, newType, ifExpression.type);
+    }
+    return result;
+  };
+
+  withStructGetter = (ctx: AliasContext, structGetter: StructGetter) => {
+    const result = deepCopy(structGetter);
+    result.source = this.withExpression(ctx, structGetter.source);
+    for (const [oldName, newType] of Object.entries(ctx.environment)) {
+      result.type = replaceType(oldName, newType, structGetter.type);
+    }
+    return result;
+  };
+
+  withOperation = (ctx: AliasContext, op: Operation) => {
+    const result = deepCopy(op);
+    result.left = this.withExpression(ctx, op.left);
+    result.right = this.withExpression(ctx, op.right);
+    for (const [oldName, newType] of Object.entries(ctx.environment)) {
+      result.type = replaceType(oldName, newType, op.type);
+    }
+    return result;
+  };
+}

packages/boringlang/src/types/type_checker.ts

@@ -0,0 +1,455 @@
+import {
+  AssignmentStatement,
+  Block,
+  containsReturn,
+  Expression,
+  Function,
+  FunctionCall,
+  FunctionDeclaration,
+  functionToType,
+  IfExpression,
+  Impl,
+  LetStatement,
+  LiteralStruct,
+  Module,
+  newVoid,
+  Operation,
+  ReturnStatement,
+  StructGetter,
+  StructTypeDeclaration,
+  TraitTypeDeclaration,
+  TypeUsage,
+  Path,
+  Identifier,
+  FunctionTypeUsage,
+} from "../parse/ast";
+import { newContext } from "./builtins";
+import { Context, deepCopy, typeExists } from "./context";
+import { TypeSystem } from "./type_system";
+
+export class TypeChecker {
+  withModule = (module: Module, typeSystem: TypeSystem) => {
+    const ctx: Context = newContext();
+    // add functions, structs, and traits to the context
+    for (const item of module.items) {
+      if (item.moduleItem === "StructTypeDeclaration") {
+        if (ctx.environment[item.name.text]) {
+          throw Error("Duplicate name of struct");
+        }
+        ctx.environment[item.name.text] = {
+          namedEntity: "NamedType",
+          isA: "Struct",
+          fields: Object.fromEntries(item.fields.map((field) => [field.name.text, field.type])),
+          impls: [],
+        };
+      }
+      if (item.moduleItem === "TraitTypeDeclaration") {
+        if (ctx.environment[item.name.text]) {
+          throw Error("Duplicate name of trait");
+        }
+        const functions: Record<string, FunctionTypeUsage> = {};
+        for (const fn of item.functions) {
+          functions[fn.name.text] = functionToType(fn);
+        }
+        ctx.environment[item.name.text] = {
+          namedEntity: "NamedType",
+          isA: "Trait",
+          fields: {},
+          impls: [
+            {
+              trait: item.name.text,
+              functions: functions,
+            },
+          ],
+        };
+      }
+      if (item.moduleItem === "Function") {
+        if (ctx.environment[item.declaration.name.text]) {
+          throw Error("Duplicate name of function");
+        }
+        ctx.environment[item.declaration.name.text] = {
+          namedEntity: "Variable",
+          type: functionToType(item.declaration),
+        };
+      }
+    }
+    // now that structs and traits are added, add impls
+    for (const item of module.items) {
+      if (item.moduleItem === "Impl") {
+        const struct = ctx.environment[item.struct.name.text];
+        if (!struct || struct.namedEntity !== "NamedType" || struct.isA !== "Struct") {
+          throw Error("Impl for non-struct");
+        }
+        const functions: Record<string, FunctionTypeUsage> = {};
+        for (const fn of item.functions) {
+          functions[fn.declaration.name.text] = functionToType(fn.declaration);
+        }
+        struct.impls.push({
+          trait: item.trait?.name.text ?? null,
+          functions: functions,
+        });
+      }
+    }
+    typeSystem.context = deepCopy(ctx);
+    // environment set up, actually recurse.
+    for (const item of module.items) {
+      if (item.moduleItem === "Function") {
+        this.withFunction(ctx, item, typeSystem);
+      }
+      if (item.moduleItem === "Impl") {
+        this.withImpl(ctx, item, typeSystem);
+      }
+      if (item.moduleItem === "StructTypeDeclaration") {
+        this.withStructDeclaration(ctx, item, typeSystem);
+      }
+      if (item.moduleItem === "TraitTypeDeclaration") {
+        this.withTrait(ctx, item, typeSystem);
+      }
+    }
+  };
+
+  withFunction = (ctx: Context, fn: Function, typeSystem: TypeSystem) => {
+    this.withFunctionDeclaration(ctx, fn.declaration, typeSystem);
+    const fnCtx = deepCopy(ctx);
+    fnCtx.currentFunctionReturn = fn.declaration.returnType;
+    for (const arg of fn.declaration.arguments) {
+      fnCtx.environment[arg.name.text] = {
+        namedEntity: "Variable",
+        type: arg.type,
+      };
+    }
+    this.withBlock(fnCtx, fn.block, typeSystem);
+    typeSystem.compare({
+      left: fn.declaration.returnType,
+      operation: { operation: "equals" },
+      right: fn.block.type,
+    });
+  };
+
+  withFunctionDeclaration = (ctx: Context, def: FunctionDeclaration, typeSystem: TypeSystem) => {
+    for (const arg of def.arguments) {
+      typeExists(ctx, arg.type);
+    }
+    typeExists(ctx, def.returnType);
+  };
+
+  withImpl = (ctx: Context, impl: Impl, typeSystem: TypeSystem) => {
+    for (const fn of impl.functions) {
+      this.withFunction(ctx, fn, typeSystem);
+    }
+  };
+
+  withStructDeclaration = (ctx: Context, struct: StructTypeDeclaration, typeSystem: TypeSystem) => {
+    for (const field of struct.fields) {
+      typeExists(ctx, field.type);
+    }
+  };
+
+  withTrait = (ctx: Context, trait: TraitTypeDeclaration, typeSystem: TypeSystem) => {
+    for (const method of trait.functions) {
+      this.withFunctionDeclaration(ctx, method, typeSystem);
+    }
+  };
+
+  withBlock = (ctx: Context, block: Block, typeSystem: TypeSystem) => {
+    const blockCtx = deepCopy(ctx);
+    for (const statement of block.statements) {
+      if (statement.statementType === "AssignmentStatement") {
+        this.withAssignmentStatement(blockCtx, statement, typeSystem);
+      }
+      if (statement.statementType === "LetStatement") {
+        this.withLetStatement(blockCtx, statement, typeSystem);
+        blockCtx.environment[statement.variableName.text] = {
+          namedEntity: "Variable",
+          type: statement.type,
+        };
+      }
+      if (statement.statementType === "Expression") {
+        this.withExpression(blockCtx, statement, typeSystem);
+      }
+      if (statement.statementType === "ReturnStatement") {
+        this.withReturnStatement(blockCtx, statement, typeSystem);
+      }
+      if (!containsReturn(block)) {
+        const lastStatement = block.statements[block.statements.length - 1] ?? null;
+        if (lastStatement && lastStatement.statementType == "Expression") {
+          typeSystem.compare({
+            left: block.type,
+            operation: { operation: "equals" },
+            right: lastStatement.type,
+          });
+        } else {
+          typeSystem.compare({
+            left: block.type,
+            operation: { operation: "equals" },
+            right: newVoid(),
+          });
+        }
+      }
+    }
+  };
+
+  withAssignmentStatement = (
+    ctx: Context,
+    statement: AssignmentStatement,
+    typeSystem: TypeSystem,
+  ) => {
+    if (statement.source.type == "StructGetter") {
+      this.withStructGetter(ctx, statement.source.source, typeSystem);
+      typeSystem.compare({
+        left: statement.source.source.type,
+        operation: { operation: "equals" },
+        right: statement.expression.type,
+      });
+    }
+    if (statement.source.type == "Identifier") {
+      typeSystem.compare({
+        left: this.withPath(ctx, {
+          expressionType: "Path",
+          value: { type: "Identifier", name: statement.source.name },
+        }),
+        operation: { operation: "equals" },
+        right: statement.expression.type,
+      });
+    }
+    this.withExpression(ctx, statement.expression, typeSystem);
+  };
+
+  withLetStatement = (ctx: Context, statement: LetStatement, typeSystem: TypeSystem) => {
+    this.withExpression(ctx, statement.expression, typeSystem);
+    typeSystem.compare({
+      left: statement.type,
+      operation: { operation: "equals" },
+      right: statement.expression.type,
+    });
+  };
+
+  withReturnStatement = (ctx: Context, statement: ReturnStatement, typeSystem: TypeSystem) => {
+    this.withExpression(ctx, statement.source, typeSystem);
+    if (ctx.currentFunctionReturn) {
+      typeSystem.compare({
+        left: ctx.currentFunctionReturn,
+        operation: { operation: "equals" },
+        right: statement.source.type,
+      });
+    }
+  };
+
+  withExpression = (ctx: Context, expression: Expression, typeSystem: TypeSystem) => {
+    if (expression.subExpression.expressionType === "LiteralInt") {
+      // LiteralInt always has type
+      typeSystem.compare({
+        left: expression.type,
+        operation: { operation: "equals" },
+        right: expression.subExpression.type,
+      });
+    }
+    if (expression.subExpression.expressionType === "LiteralFloat") {
+      // LiteralFloat always has type
+      typeSystem.compare({
+        left: expression.type,
+        operation: { operation: "equals" },
+        right: expression.subExpression.type,
+      });
+    }
+    if (expression.subExpression.expressionType === "LiteralString") {
+      // LiteralString always has type
+      typeSystem.compare({
+        left: expression.type,
+        operation: { operation: "equals" },
+        right: expression.subExpression.type,
+      });
+    }
+    if (expression.subExpression.expressionType === "LiteralBool") {
+      // LiteralBool always has type
+      typeSystem.compare({
+        left: expression.type,
+        operation: { operation: "equals" },
+        right: expression.subExpression.type,
+      });
+    }
+    if (expression.subExpression.expressionType === "LiteralStruct") {
+      this.withLiteralStruct(ctx, expression.subExpression, typeSystem);
+      typeSystem.compare({
+        left: expression.type,
+        operation: { operation: "equals" },
+        right: expression.subExpression.type,
+      });
+    }
+    if (expression.subExpression.expressionType === "FunctionCall") {
+      this.withFunctionCall(ctx, expression.subExpression, typeSystem);
+      typeSystem.compare({
+        left: expression.type,
+        operation: { operation: "equals" },
+        right: expression.subExpression.type,
+      });
+    }
+    if (expression.subExpression.expressionType === "Path") {
+      typeSystem.compare({
+        left: expression.type,
+        operation: { operation: "equals" },
+        right: this.withPath(ctx, expression.subExpression),
+      });
+    }
+    if (expression.subExpression.expressionType === "IfExpression") {
+      this.withIfExpression(ctx, expression.subExpression, typeSystem);
+      typeSystem.compare({
+        left: expression.type,
+        operation: { operation: "equals" },
+        right: expression.subExpression.type,
+      });
+    }
+    if (expression.subExpression.expressionType === "StructGetter") {
+      this.withStructGetter(ctx, expression.subExpression, typeSystem);
+      typeSystem.compare({
+        left: expression.type,
+        operation: { operation: "equals" },
+        right: expression.subExpression.type,
+      });
+    }
+    if (expression.subExpression.expressionType === "Block") {
+      this.withBlock(ctx, expression.subExpression, typeSystem);
+      typeSystem.compare({
+        left: expression.type,
+        operation: { operation: "equals" },
+        right: expression.subExpression.type,
+      });
+    }
+    if (expression.subExpression.expressionType === "Operation") {
+      this.withOperation(ctx, expression.subExpression, typeSystem);
+      typeSystem.compare({
+        left: expression.type,
+        operation: { operation: "equals" },
+        right: expression.subExpression.type,
+      });
+    }
+  };
+
+  withLiteralStruct = (ctx: Context, literal: LiteralStruct, typeSystem: TypeSystem) => {
+    const definition = ctx.environment[literal.name.text];
+    if (!definition || definition.namedEntity !== "NamedType" || !(definition.isA === "Struct")) {
+      throw new Error(`${literal.name.text} not found.`);
+    }
+    if (Object.keys(definition.fields).length !== literal.fields.length) {
+      throw new Error(`${literal.name.text} has mismatched fields.`);
+    }
+    if (new Set(Object.keys(definition.fields)).size !== literal.fields.length) {
+      throw new Error(`${literal.name.text} has repeated fields.`);
+    }
+    for (const field of literal.fields) {
+      const definitionField = definition.fields[field.name.text];
+      if (!definitionField) throw new Error(`Unknown field ${field.name.text}`);
+      this.withExpression(ctx, field.expression, typeSystem);
+      typeSystem.compare({
+        left: definitionField,
+        operation: { operation: "equals" },
+        right: field.expression.type,
+      });
+    }
+    typeSystem.compare({
+      left: { typeUsage: "NamedTypeUsage", name: literal.name },
+      operation: { operation: "equals" },
+      right: literal.type,
+    });
+  };
+
+  withFunctionCall = (ctx: Context, fnCall: FunctionCall, typeSystem: TypeSystem) => {
+    this.withExpression(ctx, fnCall.source, typeSystem);
+    typeSystem.compare({
+      left: fnCall.source.type,
+      operation: { operation: "equals" },
+      right: {
+        typeUsage: "FunctionTypeUsage",
+        arguments: fnCall.arguments.map((arg) => arg.type),
+        returnType: fnCall.type,
+      },
+    });
+    for (const [i, arg] of fnCall.arguments.entries()) {
+      this.withExpression(ctx, arg, typeSystem);
+    }
+  };
+
+  withPath = (ctx: Context, path: Path): TypeUsage => {
+    const pathList: Identifier[] = [];
+    while (path.value.type == "Nested") {
+      pathList.unshift(path.value.name);
+      path = path.value.parent;
+    }
+    pathList.unshift(path.value.name);
+
+    if (pathList.length === 0 || pathList.length > 2) {
+      throw new Error(`Namespaces not yet supported`);
+    }
+    if (pathList.length === 1) {
+      const variable = ctx.environment[pathList[0].text];
+      if (!variable || variable.namedEntity === "NamedType") {
+        throw new Error(`${pathList[0].text} not found.`);
+      }
+      return variable.type;
+    }
+
+    let struct = ctx.environment[pathList[0].text];
+    if (!struct) {
+      throw new Error(`Unknown ${pathList[0].text}`);
+    }
+    if (struct.namedEntity == "Variable") {
+      throw new Error(`Cannot "::" variable ${pathList[0].text}`);
+    }
+    if (struct.fields[pathList[1].text]) {
+      return struct.fields[pathList[1].text];
+    }
+    for (const impl of struct.impls) {
+      if (impl.functions[pathList[1].text]) {
+        return impl.functions[pathList[1].text];
+      }
+    }
+    throw new Error(`Could not find attr ${pathList[1].text}`);
+  };
+
+  withIfExpression = (ctx: Context, ifExpression: IfExpression, typeSystem: TypeSystem) => {
+    this.withExpression(ctx, ifExpression.condition, typeSystem);
+    typeSystem.compare({
+      left: { typeUsage: "NamedTypeUsage", name: { text: "bool", spanStart: 0, spanEnd: 0 } },
+      operation: { operation: "equals" },
+      right: ifExpression.condition.type,
+    });
+    this.withBlock(ctx, ifExpression.block, typeSystem);
+    typeSystem.compare({
+      left: ifExpression.block.type,
+      operation: { operation: "equals" },
+      right: ifExpression.type,
+    });
+    if (ifExpression.else) {
+      this.withBlock(ctx, ifExpression.else, typeSystem);
+      typeSystem.compare({
+        left: ifExpression.else.type,
+        operation: { operation: "equals" },
+        right: ifExpression.type,
+      });
+    }
+  };
+
+  withStructGetter = (ctx: Context, structGetter: StructGetter, typeSystem: TypeSystem) => {
+    this.withExpression(ctx, structGetter.source, typeSystem);
+    typeSystem.compare({
+      left: structGetter.source.type,
+      operation: { operation: "field", name: structGetter.attribute.text },
+      right: structGetter.type,
+    });
+  };
+
+  withOperation = (ctx: Context, op: Operation, typeSystem: TypeSystem) => {
+    this.withExpression(ctx, op.left, typeSystem);
+    this.withExpression(ctx, op.right, typeSystem);
+    typeSystem.compare({
+      left: op.left.type,
+      operation: { operation: "equals" },
+      right: op.type,
+    });
+    typeSystem.compare({
+      left: op.right.type,
+      operation: { operation: "equals" },
+      right: op.type,
+    });
+  };
+}

packages/boringlang/src/types/type_resolver.ts

@@ -0,0 +1,205 @@
+import {
+  AssignmentStatement,
+  Block,
+  containsReturn,
+  Expression,
+  Function,
+  FunctionCall,
+  FunctionDeclaration,
+  functionToType,
+  IfExpression,
+  Impl,
+  LetStatement,
+  LiteralStruct,
+  Module,
+  newVoid,
+  Operation,
+  ReturnStatement,
+  StructGetter,
+  StructTypeDeclaration,
+  TraitTypeDeclaration,
+  TypeUsage,
+  Path,
+} from "../parse/ast";
+import { newContext } from "./builtins";
+import { Context, deepCopy, typeExists } from "./context";
+import { TypeSystem } from "./type_system";
+
+export class TypeResolver {
+  withModule = (module: Module, typeSystem: TypeSystem) => {
+    const result = deepCopy(module);
+    // environment set up, actually recurse.
+    for (const [i, item] of module.items.entries()) {
+      if (item.moduleItem === "Function") {
+        result.items[i] = this.withFunction(item, typeSystem);
+      }
+      if (item.moduleItem === "Impl") {
+        result.items[i] = this.withImpl(item, typeSystem);
+      }
+      if (item.moduleItem === "StructTypeDeclaration") {
+        result.items[i] = this.withStructDeclaration(item, typeSystem);
+      }
+      if (item.moduleItem === "TraitTypeDeclaration") {
+        result.items[i] = this.withTrait(item, typeSystem);
+      }
+    }
+    return result;
+  };
+
+  withFunction = (fn: Function, typeSystem: TypeSystem) => {
+    const result = deepCopy(fn);
+    result.declaration = this.withFunctionDeclaration(fn.declaration, typeSystem);
+    result.block = this.withBlock(fn.block, typeSystem);
+    return result;
+  };
+
+  withFunctionDeclaration = (def: FunctionDeclaration, typeSystem: TypeSystem) => {
+    const result = deepCopy(def);
+    result.arguments = def.arguments.map((arg) => {
+      const resultArg = deepCopy(arg);
+      resultArg.type = typeSystem.resolveType(arg.type);
+      return resultArg;
+    });
+    return result;
+  };
+
+  withImpl = (impl: Impl, typeSystem: TypeSystem) => {
+    const result = deepCopy(impl);
+    for (const [i, fn] of impl.functions.entries()) {
+      result.functions[i] = this.withFunction(fn, typeSystem);
+    }
+    return result;
+  };
+
+  withStructDeclaration = (struct: StructTypeDeclaration, typeSystem: TypeSystem) => {
+    const result = deepCopy(struct);
+    for (const [i, field] of struct.fields.entries()) {
+      result.fields[i] = { name: field.name, type: typeSystem.resolveType(field.type) };
+    }
+    return result;
+  };
+
+  withTrait = (trait: TraitTypeDeclaration, typeSystem: TypeSystem) => {
+    const result = deepCopy(trait);
+    for (const [i, method] of trait.functions.entries()) {
+      result.functions[i] = this.withFunctionDeclaration(method, typeSystem);
+    }
+    return result;
+  };
+
+  withBlock = (block: Block, typeSystem: TypeSystem) => {
+    const result = deepCopy(block);
+    for (const [i, statement] of block.statements.entries()) {
+      if (statement.statementType === "AssignmentStatement") {
+        result.statements[i] = this.withAssignmentStatement(statement, typeSystem);
+      }
+      if (statement.statementType === "LetStatement") {
+        result.statements[i] = this.withLetStatement(statement, typeSystem);
+      }
+      if (statement.statementType === "Expression") {
+        result.statements[i] = this.withExpression(statement, typeSystem);
+      }
+      if (statement.statementType === "ReturnStatement") {
+        result.statements[i] = this.withReturnStatement(statement, typeSystem);
+      }
+      result.type = typeSystem.resolveType(block.type);
+    }
+    return result;
+  };
+
+  withAssignmentStatement = (statement: AssignmentStatement, typeSystem: TypeSystem) => {
+    const result = deepCopy(statement);
+    if (statement.source.type == "StructGetter") {
+      result.source = {
+        type: "StructGetter",
+        source: this.withStructGetter(statement.source.source, typeSystem),
+      };
+    }
+    result.expression = this.withExpression(statement.expression, typeSystem);
+    return result;
+  };
+
+  withLetStatement = (statement: LetStatement, typeSystem: TypeSystem) => {
+    const result = deepCopy(statement);
+    result.expression = this.withExpression(statement.expression, typeSystem);
+    result.type = typeSystem.resolveType(statement.type);
+    return result;
+  };
+
+  withReturnStatement = (statement: ReturnStatement, typeSystem: TypeSystem) => {
+    const result = deepCopy(statement);
+    result.source = this.withExpression(statement.source, typeSystem);
+    return result;
+  };
+
+  withExpression = (expression: Expression, typeSystem: TypeSystem) => {
+    const result = deepCopy(expression);
+    result.type = typeSystem.resolveType(expression.type);
+
+    if (expression.subExpression.expressionType === "LiteralStruct") {
+      result.subExpression = this.withLiteralStruct(expression.subExpression, typeSystem);
+    }
+    if (expression.subExpression.expressionType === "FunctionCall") {
+      result.subExpression = this.withFunctionCall(expression.subExpression, typeSystem);
+    }
+    if (expression.subExpression.expressionType === "Path") {
+      // paths do not have types
+    }
+    if (expression.subExpression.expressionType === "IfExpression") {
+      result.subExpression = this.withIfExpression(expression.subExpression, typeSystem);
+    }
+    if (expression.subExpression.expressionType === "StructGetter") {
+      result.subExpression = this.withStructGetter(expression.subExpression, typeSystem);
+    }
+    if (expression.subExpression.expressionType === "Block") {
+      result.subExpression = this.withBlock(expression.subExpression, typeSystem);
+    }
+    if (expression.subExpression.expressionType === "Operation") {
+      result.subExpression = this.withOperation(expression.subExpression, typeSystem);
+    }
+    return result;
+  };
+
+  withLiteralStruct = (literal: LiteralStruct, typeSystem: TypeSystem) => {
+    const result = deepCopy(literal);
+    for (const [i, field] of literal.fields.entries()) {
+      result.fields[i].expression = this.withExpression(field.expression, typeSystem);
+    }
+    result.type = typeSystem.resolveType(literal.type);
+    return result;
+  };
+
+  withFunctionCall = (fnCall: FunctionCall, typeSystem: TypeSystem) => {
+    const result = deepCopy(fnCall);
+    result.type = typeSystem.resolveType(fnCall.type);
+    result.source = this.withExpression(fnCall.source, typeSystem);
+    for (const [i, arg] of fnCall.arguments.entries()) {
+      result.arguments[i] = this.withExpression(arg, typeSystem);
+    }
+    return result;
+  };
+
+  withIfExpression = (ifExpression: IfExpression, typeSystem: TypeSystem) => {
+    const result = deepCopy(ifExpression);
+    result.type = typeSystem.resolveType(ifExpression.type);
+    result.condition = this.withExpression(ifExpression.condition, typeSystem);
+    result.block = this.withBlock(ifExpression.block, typeSystem);
+    result.else = ifExpression.else ? this.withBlock(ifExpression.else, typeSystem) : null;
+    return result;
+  };
+
+  withStructGetter = (structGetter: StructGetter, typeSystem: TypeSystem) => {
+    const result = deepCopy(structGetter);
+    result.type = typeSystem.resolveType(structGetter.type);
+    result.source = this.withExpression(structGetter.source, typeSystem);
+    return result;
+  };
+
+  withOperation = (op: Operation, typeSystem: TypeSystem) => {
+    const result = deepCopy(op);
+    result.type = typeSystem.resolveType(op.type);
+    result.left = this.withExpression(op.left, typeSystem);
+    result.right = this.withExpression(op.right, typeSystem);
+    return result;
+  };
+}

packages/boringlang/src/types/type_system.ts

@@ -0,0 +1,203 @@
+import { FunctionTypeUsage, TypeUsage, UnknownTypeUsage } from "../parse/ast";
+import { newContext } from "./builtins";
+import { Context, deepCopy, getAttr } from "./context";
+
+export const compareTypes = (typeA: TypeUsage, typeB: TypeUsage) => {
+  if (typeA.typeUsage !== typeB.typeUsage) {
+    throw Error(
+      `Mismatched types: ${JSON.stringify(typeA, null, 2)} ${JSON.stringify(typeB, null, 2)}`,
+    );
+  }
+  if (typeA.typeUsage == "NamedTypeUsage" && typeB.typeUsage == "NamedTypeUsage") {
+    if (typeB.name.text === "Never") {
+      // never matches with everything
+      return;
+    }
+    if (typeA.name.text !== typeB.name.text) {
+      throw Error(
+        `Mismatched types: ${typeA.name.text}:${typeA.name.spanStart}:${typeA.name.spanEnd} ${typeB.name.text}:${typeB.name.spanStart}:${typeB.name.spanEnd}`,
+      );
+    }
+  }
+  if (typeA.typeUsage == "FunctionTypeUsage" && typeB.typeUsage == "FunctionTypeUsage") {
+    if (typeA.arguments.length !== typeB.arguments.length) {
+      throw Error(`Mismatched arg lengths: ${typeA.arguments.length} ${typeB.arguments.length}`);
+    }
+    for (let i = 0; i < typeA.arguments.length; i++) {
+      compareTypes(typeA.arguments[i], typeB.arguments[i]);
+    }
+    compareTypes(typeA.returnType, typeB.returnType);
+  }
+};
+
+interface Equals {
+  operation: "equals";
+}
+
+interface Field {
+  operation: "field";
+  name: string;
+}
+
+interface Comparison {
+  left: TypeUsage;
+  operation: Equals | Field;
+  right: TypeUsage;
+}
+
+export class TypeSystem {
+  comparisons: Comparison[];
+  result: Record<string, TypeUsage>;
+  context: Context;
+
+  constructor() {
+    this.comparisons = [];
+    this.result = {};
+    this.context = newContext();
+  }
+
+  compare = (comparison: Comparison) => {
+    this.comparisons.push(comparison);
+  };
+
+  solve = () => {
+    let foundUpdate = false;
+    while (true) {
+      foundUpdate = false;
+      for (const comparison of this.comparisons) {
+        // if already found, just update
+        comparison.left = this.resolveType(comparison.left);
+        comparison.right = this.resolveType(comparison.right);
+        // equals
+        if (comparison.operation.operation === "equals") {
+          const [result, found] = this.equateTypes(comparison.left, comparison.right);
+          if (found) {
+            comparison.left = result;
+            comparison.right = result;
+            foundUpdate = true;
+          }
+          // check
+          if (
+            comparison.left.typeUsage !== "UnknownTypeUsage" &&
+            comparison.right.typeUsage !== "UnknownTypeUsage"
+          ) {
+            compareTypes(comparison.left, comparison.right);
+          }
+        }
+        // field
+        if (comparison.operation.operation === "field") {
+          if (comparison.left.typeUsage === "UnknownTypeUsage") {
+            // cannot yet be resolved
+            continue;
+          }
+          if (comparison.left.typeUsage !== "NamedTypeUsage") {
+            throw Error("field on something that isn't a named type.");
+          }
+          // cannot be solved left
+          // solve right
+          if (comparison.right.typeUsage === "UnknownTypeUsage") {
+            foundUpdate = true;
+            const attrType = getAttr(
+              this.context,
+              comparison.left.name.text,
+              comparison.operation.name,
+            );
+            const [result, found] = this.equateTypes(attrType, comparison.right);
+            if (found) {
+              comparison.right = result;
+              foundUpdate = true;
+            }
+          }
+          // check
+          if (comparison.right.typeUsage !== "UnknownTypeUsage") {
+            const attrType = getAttr(
+              this.context,
+              comparison.left.name.text,
+              comparison.operation.name,
+            );
+            compareTypes(attrType, comparison.right);
+          }
+        }
+      }
+      let containsUnknown = false;
+      for (const comparison of this.comparisons) {
+        if (this.containsUnknown(comparison.left) || this.containsUnknown(comparison.right)) {
+          containsUnknown = true;
+        }
+      }
+      if (!foundUpdate && containsUnknown) {
+        throw Error("Type system failed to resolve all unknowns");
+      }
+      if (!foundUpdate) {
+        break;
+      }
+    }
+    return this.result;
+  };
+
+  equateTypes = (left: TypeUsage, right: TypeUsage): [TypeUsage, boolean] => {
+    if (left.typeUsage === "UnknownTypeUsage" && right.typeUsage !== "UnknownTypeUsage") {
+      this.result[left.name] = right;
+      return [right, true];
+    }
+    if (left.typeUsage !== "UnknownTypeUsage" && right.typeUsage === "UnknownTypeUsage") {
+      this.result[right.name] = left;
+      return [left, true];
+    }
+    if (left.typeUsage === "FunctionTypeUsage" && right.typeUsage === "FunctionTypeUsage") {
+      if (left.arguments.length !== right.arguments.length) {
+        throw Error(`Mismatched arg lengths: ${left.arguments.length} ${right.arguments.length}`);
+      }
+      let found = false;
+      let fnResult: FunctionTypeUsage = deepCopy(left);
+      for (let i = 0; i < left.arguments.length; i++) {
+        const [result, wasFound] = this.equateTypes(left.arguments[i], right.arguments[i]);
+        if (wasFound) {
+          found = true;
+        }
+        fnResult.arguments[i] = result;
+      }
+      const [result, wasFound] = this.equateTypes(left.returnType, right.returnType);
+      if (wasFound) {
+        found = true;
+      }
+      fnResult.returnType = result;
+      return [fnResult, found];
+    }
+    return [left, false];
+  };
+
+  resolveType = (type: TypeUsage): TypeUsage => {
+    if (type.typeUsage === "UnknownTypeUsage") {
+      if (this.result[type.name]) {
+        return this.result[type.name];
+      }
+      return type;
+    }
+    if (type.typeUsage === "NamedTypeUsage") {
+      return type;
+    }
+    return {
+      typeUsage: "FunctionTypeUsage",
+      arguments: type.arguments.map((arg) => this.resolveType(arg)),
+      returnType: this.resolveType(type.returnType),
+    };
+  };
+
+  containsUnknown = (type: TypeUsage) => {
+    if (type.typeUsage === "UnknownTypeUsage") {
+      return true;
+    }
+    if (type.typeUsage === "FunctionTypeUsage") {
+      for (const arg of type.arguments) {
+        if (this.containsUnknown(arg)) {
+          return true;
+        }
+      }
+      if (this.containsUnknown(type.returnType)) {
+        return true;
+      }
+    }
+    return false;
+  };
+}