lambdas and application now in AST, types and interpreter

src/ast.ts

@@ -1,4 +1,4 @@
-import type { Value } from './types';
+import type { Value, Closure } from './types';
 
 export type Literal = {
     kind: 'literal'
@@ -31,4 +31,16 @@ export type If = {
     else: AST
 }
 
-export type AST = Literal | BinaryOp | Variable | Let | If
+export type Lambda = {
+    kind: 'lambda'
+    params: string[]
+    body: AST
+}
+
+export type Apply = {
+    kind: 'apply'
+    func: AST
+    args: AST[]
+}
+
+export type AST = Literal | BinaryOp | Variable | Let | If | Lambda | Apply