Adding spread operator. starting to build a stdlib. omg

src/ast.ts

@@ -59,13 +59,14 @@ export type Pattern =
     | { kind: 'literal', value: number | string }
     | { kind: 'constructor', name: string, args: Pattern[] }
     | { kind: 'list', elements: Pattern[] }
+    | { kind: 'list-spread', head: Pattern[], spread: string }
     | { kind: 'record', fields: { [key: string]: Pattern } }
 
 // Data Structures
 
 export type List = {
     kind: 'list'
-    elements: AST[]
+    elements: (AST | { spread: AST })[]
 }
 
 export type Record = {

src/interpreter.ts

@@ -16,11 +16,25 @@ export function evaluate(ast: AST, env: Env): Value {
             return val;
         }
 
-        case 'list':
-            return {
-                kind: 'list',
-                elements: ast.elements.map(el => evaluate(el, env))
-            };
+        case 'list': {
+            const elements: Value[] = [];
+
+            for (const item of ast.elements) {
+                // Spread
+                if ('spread' in item) {
+                    const spreadValue = evaluate(item.spread, env);
+
+                    if (spreadValue.kind !== 'list')
+                        throw new Error('can only spread lists');
+
+                    elements.push(...spreadValue.elements);
+                } else {
+                    elements.push(evaluate(item, env));
+                }
+            }
+
+            return { kind: 'list', elements };
+        }
 
         case 'record':
             const fields: { [key: string]: Value } = {};
@@ -226,6 +240,23 @@ function matchPattern(value: Value, pattern: Pattern): Bindings | null {
             return bindings;
         }
 
+        case 'list-spread': {
+            if (value.kind !== 'list') return null;
+            if (value.elements.length < pattern.head.length) return null;
+
+            const bindings: Bindings = {};
+            for (let i = 0; i < pattern.head.length; i++) {
+                const elemBindings = matchPattern(value.elements[i], pattern.head[i]);
+                if (elemBindings === null) return null;
+                Object.assign(bindings, elemBindings);
+            }
+
+            const rest = value.elements.slice(pattern.head.length);
+            bindings[pattern.spread] = { kind: 'list', elements: rest };
+
+            return bindings;
+        }
+
         case 'record': {
             if (value.kind !== 'record') return null;
 

src/lexer.ts

@@ -33,6 +33,7 @@ export type Token =
     | { kind: 'ampersand' }
     | { kind: 'underscore' }
     | { kind: 'dot' }
+    | { kind: 'dot-dot-dot' }
     | { kind: 'at' }
 
     // Anithmetic
@@ -148,7 +149,7 @@ export function tokenize(source: string): Token[] {
 
         switch (char) {
             case '>': {
-                if (source[i + 1] == '=') {
+                if (source[i + 1] === '=') {
                     tokens.push({ kind: 'greater-equals' });
                     i++;
                 } else {
@@ -157,7 +158,7 @@ export function tokenize(source: string): Token[] {
                 break;
             }
             case '<': {
-                if (source[i + 1] == '=') {
+                if (source[i + 1] === '=') {
                     tokens.push({ kind: 'less-equals' });
                     i++;
                 } else {
@@ -166,7 +167,7 @@ export function tokenize(source: string): Token[] {
                 break;
             }
             case '=': {
-                if (source[i + 1] == '=') {
+                if (source[i + 1] === '=') {
                     tokens.push({ kind: 'equals-equals' });
                     i++;
                 } else {
@@ -175,7 +176,7 @@ export function tokenize(source: string): Token[] {
                 break;
             }
             case '!': {
-                if (source[i + 1] == '=') {
+                if (source[i + 1] === '=') {
                     tokens.push({ kind: 'not-equals' });
                     i++;
                 } else {
@@ -183,6 +184,15 @@ export function tokenize(source: string): Token[] {
                 }
                 break;
             }
+            case '.': {
+                if (source[i + 1] === '.' && source[i + 2] === '.') {
+                    tokens.push({ kind: 'dot-dot-dot' })
+                    i += 2;
+                } else {
+                    tokens.push({ kind: 'dot' });
+                }
+                break;
+            }
             case ':': tokens.push({ kind: 'colon' }); break;
             case ';': tokens.push({ kind: 'semicolon' }); break;
             case '\\': tokens.push({ kind: 'backslash' }); break;
@@ -190,7 +200,6 @@ export function tokenize(source: string): Token[] {
             case '|': tokens.push({ kind: 'pipe' }); break;
             case ',': tokens.push({ kind: 'comma' }); break;
             case '&': tokens.push({ kind: 'ampersand' }); break;
-            case '.': tokens.push({ kind: 'dot' }); break;
             case '@': tokens.push({ kind: 'at' }); break;
 
             // Arithmetic

src/main.ts

@@ -2,21 +2,29 @@ import { evaluate } from './interpreter'
 import type { Env } from './env'
 import { tokenize } from './lexer'
 import { Parser } from './parser'
-import cgCode from './counter.cg?raw';
 import { runApp } from './runtime';
 import { builtins } from './builtins';
 
+import counterApp from './counter.cg?raw';
+import stdlibCode from './stdlib.cg?raw';
+import testCode from './test.cg?raw';
+
 const canvas = document.createElement('canvas');
 canvas.width = 800;
 canvas.height = 600;
 document.body.appendChild(canvas);
 
+const cgCode = stdlibCode + '\n' + testCode;
+
 const tokens = tokenize(cgCode);
 const parser = new Parser(tokens);
 const ast = parser.parse();
 console.log(ast);
 
 const env: Env = new Map(Object.entries(builtins));
+const res = evaluate(ast, env);
+console.log(res);
+/*
 const appRecord = evaluate(ast, env);
 
 console.log(appRecord);
@@ -29,3 +37,4 @@ const update = appRecord.fields.update;
 const view = appRecord.fields.view;
 
 runApp({ init, update, view }, canvas);
+*/

src/parser.ts

@@ -181,14 +181,29 @@ export class Parser {
             this.advance();
             const elements: Pattern[] = [];
             let first = true;
+            let spreadName: string | null = null;
 
             while (this.current().kind !== 'close-bracket') {
                 if (!first) this.expect('comma');
                 first = false;
+
+                // Spread
+                if (this.current().kind === 'dot-dot-dot') {
+                    this.advance();
+                    const nameToken = this.expect('ident');
+                    spreadName = (nameToken as { value: string }).value;
+                    break;
+                }
+
                 elements.push(this.parsePattern());
             }
 
             this.expect('close-bracket');
+
+            if (spreadName !== null) {
+                return { kind: 'list-spread', head: elements, spread: spreadName };
+            }
+
             return { kind: 'list', elements };
         }
 
@@ -356,7 +371,7 @@ export class Parser {
         if (token.kind === 'open-bracket') {
             this.advance();
 
-            const items: AST[] = [];
+            const items: (AST | { spread: AST })[] = [];
             let first = true;
 
             while (this.current().kind !== 'close-bracket') {
@@ -365,7 +380,14 @@ export class Parser {
                 }
                 first = false;
 
-                items.push(this.parseExpression());
+                // Spread
+                if (this.current().kind === 'dot-dot-dot') {
+                    this.advance();
+                    const expr = this.parseExpression();
+                    items.push({ spread: expr })
+                } else {
+                    items.push(this.parseExpression());
+                }
             }
 
             this.expect('close-bracket');

src/stdlib.cg

@@ -0,0 +1,9 @@
+map = f list \ list
+  | [] \ []
+  | [x, ...xs] \ [f x, ...map f xs];
+
+filter = f list \ list
+  | [] \ []
+  | [x, ...xs] \ (f x
+      | True \ [x, ...filter f xs]
+      | False \ filter f xs);

src/test.cg

@@ -0,0 +1,7 @@
+add1 = x \ x + 1;
+
+mapped = map add1 [1, 2, 3, 4, 5];
+
+isEven = x \ x % 2 == 0;
+
+filter isEven mapped