Start lowering

src/ast.ts

@@ -20,9 +20,10 @@ export type Item = ItemKind & {
 
 export type FunctionDef = {
   name: string;
-  args: FunctionArg[];
+  params: FunctionArg[];
   body: Expr;
   returnType?: Type;
+  ty?: TyFn;
 };
 
 export type FunctionArg = {
@@ -253,6 +254,11 @@ export function tyIsUnit(ty: Ty): ty is TyUnit {
   return ty.kind === "tuple" && ty.elems.length === 0;
 }
 
+export const TY_UNIT: Ty = { kind: "tuple", elems: [] };
+export const TY_STRING: Ty = { kind: "string" };
+export const TY_BOOL: Ty = { kind: "bool" };
+export const TY_INT: Ty = { kind: "int" };
+
 // folders
 
 export type FoldFn<T> = (value: T) => T;
@@ -279,14 +285,14 @@ export const DEFAULT_FOLDER: Folder = {
   },
 };
 
-export function fold_ast(ast: Ast, folder: Folder): Ast {
+export function foldAst(ast: Ast, folder: Folder): Ast {
   return ast.map((item) => folder.item(item));
 }
 
 export function superFoldItem(item: Item, folder: Folder): Item {
   switch (item.kind) {
     case "function": {
-      const args = item.node.args.map(({ name, type, span }) => ({
+      const args = item.node.params.map(({ name, type, span }) => ({
         name,
         type: folder.type(type),
         span,
@@ -297,7 +303,7 @@ export function superFoldItem(item: Item, folder: Folder): Item {
         span: item.span,
         node: {
           name: item.node.name,
-          args,
+          params: args,
           body: folder.expr(item.node.body),
           returnType: item.node.returnType && folder.type(item.node.returnType),
         },
@@ -399,3 +405,7 @@ export function superFoldType(type: Type, folder: Folder): Type {
     }
   }
 }
+
+export function varUnreachable(): never {
+  throw new Error("Type variables must not occur after type checking");
+}

src/parser.ts

@@ -76,7 +76,7 @@ function parseItem(t: Token[]): [Token[], Item] {
 
     const def: FunctionDef = {
       name: name.ident,
-      args,
+      params: args,
       returnType,
       body,
     };

src/printer.ts

@@ -23,7 +23,7 @@ function printItem(item: Item): string {
 }
 
 function printFunction(func: FunctionDef): string {
-  const args = func.args
+  const args = func.params
     .map(({ name, type }) => `${name}: ${printType(type)}`)
     .join(", ");
   const ret = func.returnType ? `: ${printType(func.returnType)}` : "";

src/resolve.ts

@@ -4,7 +4,7 @@ import {
   Folder,
   Identifier,
   Resolution,
-  fold_ast,
+  foldAst,
   superFoldExpr,
   superFoldItem,
 } from "./ast";
@@ -78,7 +78,7 @@ export function resolve(ast: Ast): Ast {
     item(item) {
       switch (item.kind) {
         case "function": {
-          const args = item.node.args.map(({ name, span, type }) => ({
+          const params = item.node.params.map(({ name, span, type }) => ({
             name,
             span,
             type: this.type(type),
@@ -86,16 +86,16 @@ export function resolve(ast: Ast): Ast {
           const returnType =
             item.node.returnType && this.type(item.node.returnType);
 
-          item.node.args.forEach(({ name }) => scopes.push(name));
+          item.node.params.forEach(({ name }) => scopes.push(name));
           const body = superFoldExpr(item.node.body, this);
-          item.node.args.forEach(({ name }) => popScope(name));
+          item.node.params.forEach(({ name }) => popScope(name));
 
           return {
             kind: "function",
             span: item.span,
             node: {
               name: item.node.name,
-              args,
+              params,
               returnType,
               body,
             },
@@ -132,7 +132,7 @@ export function resolve(ast: Ast): Ast {
     },
   };
 
-  const resolved = fold_ast(ast, resolver);
+  const resolved = foldAst(ast, resolver);
 
   return resolved;
 }

src/typeck.ts

@@ -1,36 +1,35 @@
 import {
   Ast,
+  binaryExprPrecedenceClass,
   COMPARISON_KINDS,
   DEFAULT_FOLDER,
   EQUALITY_KINDS,
   Expr,
   ExprBinary,
   ExprUnary,
+  foldAst,
   Folder,
   Identifier,
   LOGICAL_KINDS,
   Resolution,
   Ty,
+  TY_BOOL,
+  TY_INT,
+  TY_STRING,
+  TY_UNIT,
   TyFn,
   Type,
-  binaryExprPrecedenceClass,
-  fold_ast,
 } from "./ast";
 import { CompilerError, Span } from "./error";
 import { printTy } from "./printer";
 
-const TY_UNIT: Ty = { kind: "tuple", elems: [] };
-const TY_STRING: Ty = { kind: "string" };
-const TY_BOOL: Ty = { kind: "bool" };
-const TY_INT: Ty = { kind: "int" };
-
 function builtinAsTy(name: string, span: Span): Ty {
   switch (name) {
     case "String": {
       return TY_STRING;
     }
     case "Int": {
-      return TY_INT;
+      return TY_BOOL;
     }
     case "Bool": {
       return TY_BOOL;
@@ -105,7 +104,7 @@ export function typeck(ast: Ast): Ast {
     const item = ast[index];
     switch (item.kind) {
       case "function": {
-        const args = item.node.args.map((arg) => lowerAstTy(arg.type));
+        const args = item.node.params.map((arg) => lowerAstTy(arg.type));
         const returnTy: Ty = item.node.returnType
           ? lowerAstTy(item.node.returnType)
           : TY_UNIT;
@@ -153,7 +152,7 @@ export function typeck(ast: Ast): Ast {
             kind: "function",
             node: {
               name: item.node.name,
-              args: item.node.args.map((arg, i) => ({
+              params: item.node.params.map((arg, i) => ({
                 ...arg,
                 type: { ...arg.type, ty: fnTy.params[i] },
               })),
@@ -162,15 +161,14 @@ export function typeck(ast: Ast): Ast {
             },
             span: item.span,
             id: item.id,
+            ty: fnTy,
           };
         }
       }
     },
   };
 
-  const withTypes = fold_ast(ast, checker);
+  return foldAst(ast, checker);
-
-  return withTypes;
 }
 
 type TyVarRes =