Typeclasses

src/ast.ts

@@ -187,6 +187,25 @@ export type Constraint = {
     typeVar: string
 }
 
+export type ClassDefinition = {
+    kind: 'class-definition'
+    name: string
+    param: string
+    methods: { name: string, type: TypeAST }[]
+    line?: number
+    column?: number
+    start?: number
+}
+
+export type InstanceDeclaration = {
+    kind: 'instance-declaration'
+    typeName: string
+    className: string
+    line?: number
+    column?: number
+    start?: number
+}
+
 export type AST =
     | Literal
     | Variable

src/cg/01-stdlib.cg

@@ -3,14 +3,22 @@ getX : { x : Int, y : Int } \ Int = p \ p.x;
 setX : Int \ { x : Int, y : Int } \ { x : Int, y : Int } = newX p \ p.{ x = newX };
 myPoint = point 3 Blah;
 
-# builtins
+Num a {
-# TODO: once we get typeclasses, make these the actual types
-cat : a \ a \ a;
   add : a \ a \ a;
   sub : a \ a \ a;
   mul : a \ a \ a;
   div : a \ a \ a;
-eq : a \ a \ Bool;
+};
+
+Int : Num;
+Float : Num;
+
+Eq a { eq : a \ a \ Bool }
+Int : Eq;
+String : Eq;
+
+Semigroup a { cat : a \ a \ a };
+String : Semigroup;
 
 Maybe a = None | Some a;
 Bool = True | False;

src/compiler.ts

@@ -1,4 +1,4 @@
-import type { AST, Pattern, Definition } from './ast';
+import type { AST, Pattern, Definition, TypeDefinition, ClassDefinition, InstanceDeclaration } from './ast';
 import { store } from './runtime-js';
 import { typecheck } from './typechecker';
 
@@ -221,8 +221,8 @@ function compilePattern(pattern: Pattern, expr: string): { condition: string, bi
     }
 }
 
-export function compileAndRun(defs: Definition[], typeDefs: TypeDefinition[] = []) {
+export function compileAndRun(defs: Definition[], typeDefs: TypeDefinition[] = [], classDefs: ClassDefinition[] = [], instances: InstanceDeclaration[] = []) {
-    typecheck(defs, typeDefs);
+    typecheck(defs, typeDefs, classDefs, instances);
 
     const compiledDefs: string[] = [];
 

src/main.ts

@@ -23,13 +23,13 @@ store.viewport = { width: window.innerWidth, height: window.innerHeight };
 try {
     const tokens = tokenize(cgCode);
     const parser = new Parser(tokens, cgCode);
-    const { definitions: defs, typeDefinitions: typeDefs } = parser.parse();
+    const { definitions: defs, typeDefinitions: typeDefs, classDefinitions: classDefs, instanceDeclarations: instances } = parser.parse();
     loadDefinitions();
 
     // TODO remove once we're booting from store, files are backup
     if (!store.paletteHistory) store.paletteHistory = [];
 
-    compileAndRun(defs, typeDefs);
+    compileAndRun(defs, typeDefs, classDefs, instances);
     saveDefinitions();
 
     runAppCompiled(canvas, store);

src/parser.ts

@@ -1,5 +1,5 @@
 import type { Token } from './lexer'
-import type { AST, MatchCase, Pattern, Definition, TypeAST, TypeDefinition, TypeConstructor, Annotation } from './ast'
+import type { AST, MatchCase, Pattern, Definition, TypeAST, TypeDefinition, TypeConstructor, Annotation, ClassDefinition, InstanceDeclaration } from './ast'
 import { ParseError } from './error'
 
 export class Parser {
@@ -150,20 +150,32 @@ export class Parser {
         }
     }
 
-    parse(): { definitions: Definition[], typeDefinitions: TypeDefinition[] } {
+    parse(): { definitions: Definition[], typeDefinitions: TypeDefinition[], classDefinitions: ClassDefinition[], instanceDeclarations: InstanceDeclaration[] } {
         const definitions: Definition[] = [];
         const typeDefinitions: TypeDefinition[] = [];
+        const classDefinitions: ClassDefinition[] = [];
+        const instanceDeclarations: InstanceDeclaration[] = [];
 
         while (this.current().kind !== 'eof') {
             if (this.current().kind === 'type-ident') {
+                let offset = 1;
+                while (this.peek(offset).kind === 'ident') offset++;
+                const after = this.peek(offset);
+
+                if (after.kind === 'open-brace') {
+                    classDefinitions.push(this.parseClassDefinition());
+                } else if (after.kind === 'colon') {
+                    instanceDeclarations.push(this.parseInstanceDeclaration());
+                } else {
                     typeDefinitions.push(this.parseTypeDefinition());
+                }
                 continue;
             }
 
             definitions.push(this.parseDefinition());
         }
 
-        return { definitions, typeDefinitions };
+        return { definitions, typeDefinitions, classDefinitions, instanceDeclarations };
     }
 
     private parseDefinition(): Definition {
@@ -662,4 +674,32 @@ export class Parser {
         }
         return { name, args };
     }
+
+    private parseClassDefinition(): ClassDefinition {
+        const nameToken = this.advance();
+        const param = (this.expect('ident') as { value: string }).value;
+
+        this.expect('open-brace');
+        const methods: { name: string, type: TypeAST }[] = [];
+        while (this.current().kind !== 'close-brace') {
+            const methodName = (this.expect('ident') as { value: string }).value;
+            this.expect('colon');
+            const type = this.parseType();
+            methods.push({ name: methodName, type });
+            if (this.current().kind === 'semicolon') this.advance();
+        }
+        this.expect('close-brace');
+        if (this.current().kind === 'semicolon') this.advance();
+
+        return { kind: 'class-definition', name: (nameToken as { value: string }).value, param, methods, ...this.getPos(nameToken) };
+    }
+
+    private parseInstanceDeclaration(): InstanceDeclaration {
+        const typeToken = this.advance();
+        this.expect('colon');
+        const classToken = this.expect('type-ident');
+        if (this.current().kind === 'semicolon') this.advance();
+
+        return { kind: 'instance-declaration', typeName: (typeToken as { value: string }).value, className: (classToken as { value: string }).value, ...this.getPos(typeToken) };
+    }
 }

src/typechecker.ts

@@ -1,4 +1,4 @@
-import type { AST, TypeAST, Pattern, Definition, TypeDefinition } from './ast'
+import type { AST, TypeAST, Pattern, Definition, TypeDefinition, ClassDefinition, InstanceDeclaration } from './ast'
 import { prettyPrintType } from './ast'
 
 // Map type var names to their types
@@ -155,6 +155,24 @@ function infer(expr: AST, env: TypeEnv, subst: Subst): TypeAST | null {
                 if (err) warn(err, arg);
                 current = applySubst(current.result, subst);
             }
+
+            // Check typeclass constraints
+            if (expr.func.kind === 'variable') {
+                const constraint = moduleConstraints.get(expr.func.name);
+                if (constraint) {
+                    const argType = infer(expr.args[0], env, subst);
+                    if (argType) {
+                        const resolved = applySubst(argType, subst);
+                        if (resolved.kind === 'type-name') {
+                            const instances = moduleInstances.get(constraint.className);
+                            if (!instances || !instances.has(resolved.name)) {
+                                warn(`No instance ${constraint.className} ${resolved.name}`, expr);
+                            }
+                        }
+                    }
+                }
+            }
+
             return current;
         }
 
@@ -309,9 +327,28 @@ function bindPattern(pattern: Pattern, type: TypeAST, env: TypeEnv, subst: Subst
     }
 }
 
-export function typecheck(defs: Definition[], typeDefs: TypeDefinition[] = []) {
+let moduleConstraints = new Map<string, { param: string, className: string }>();
+let moduleInstances = new Map<string, Set<string>>();
+
+export function typecheck(defs: Definition[], typeDefs: TypeDefinition[] = [], classDefs: ClassDefinition[] = [], instances: InstanceDeclaration[] = []) {
     const env: TypeEnv = new Map();
 
+    // Register instances as a lookup: className -> Set of type names
+    const instanceMap = new Map<string, Set<string>>();
+    for (const inst of instances) {
+        if (!instanceMap.has(inst.className)) instanceMap.set(inst.className, new Set());
+        instanceMap.get(inst.className)!.add(inst.typeName);
+    }
+    moduleInstances = instanceMap;
+
+    // Register class methods with constraints in env
+    for (const cls of classDefs) {
+        for (const method of cls.methods) {
+            env.set(method.name, method.type);
+            moduleConstraints.set(method.name, { param: cls.param, className: cls.name });
+        }
+    }
+
     // Register constructors
     for (const td of typeDefs) {
         const resultType: TypeAST = td.params.length === 0