feat: add symbols, split empty type

packages/builder/src/ast.ts

@@ -6,7 +6,7 @@ import { AstType } from './ast/type.js';
  * identifier for ast types
  */
 type Ast<T extends string> = {
-  kind: T,
+  readonly kind: T,
   span: Span,
 }
 

packages/builder/src/fn.ts

@@ -3,7 +3,6 @@ import { Span } from '@mcslib/core';
 import { McsEmpty } from './primitive.js';
 import { VarType } from './var.js';
 
-
 export type Fn<Sig extends FnSig = FnSig> = {
   span: Span,
   args: CallArgs<Sig['args']>,

packages/builder/src/primitive.ts

@@ -1,9 +1,3 @@
-import { AstType } from './ast/type.js';
-import { Primitive } from './primitive/base.js';
-
+export * from './primitive/empty.js';
 export * from './primitive/number.js';
 export * from './primitive/string.js';
-
-export class McsEmpty extends Primitive {
-  static readonly type: AstType = 'empty';
-}

packages/builder/src/primitive/empty.ts

@@ -0,0 +1,6 @@
+import { AstType } from '@/ast/type.js';
+import { Primitive } from './base.js';
+
+export class McsEmpty extends Primitive {
+  static readonly type: AstType = 'empty';
+}

packages/builder/src/symbol.ts

@@ -0,0 +1,11 @@
+export const McsSymbol = Object.freeze({
+  serialize: Symbol('McsSymbol.serialize'),
+
+  add: Symbol('McsSymbol.add'),
+  sub: Symbol('McsSymbol.sub'),
+  mul: Symbol('McsSymbol.mul'),
+  div: Symbol('McsSymbol.div'),
+  remi: Symbol('McsSymbol.remi'),
+
+  iterable: Symbol('McsSymbol.iterable'),
+});