1 files changed, 56 insertions, 14 deletions
diff --git a/src/lib/core/eval.ts b/src/lib/core/eval.ts
index 74801bf..65e4788 100644
--- a/src/lib/core/eval.ts
+++ b/src/lib/core/eval.ts
@@ -26,25 +26,67 @@ export type UnarrayIfOnlyHead<T extends readonly any[]> = T extends [
   ? Head
   : T;
 
-export type BUILTIN_ARR<Args extends readonly ASTNode[]> = {
-  [Idx in keyof Args]: Args[Idx] extends ASTNode ? Evaluate<Args[Idx]> : never;
-};
+export type NumberToArray<
+  Number extends number,
+  Carry extends readonly any[] = []
+> = Number extends Carry["length"]
+  ? Carry
+  : NumberToArray<Number, [...Carry, any]>;
 
-export type BUILTIN_ToString<Args extends readonly ASTNode[]> = ToStringInner<
+export type NumbersToArray<
+  Numbers extends readonly number[],
+  Carry extends readonly any[] = []
+> = Numbers extends [
+  infer Head extends number,
+  ...infer Tail extends readonly number[]
+]
+  ? NumbersToArray<Tail, [...Carry, ...NumberToArray<Head>]>
+  : Carry;
+
+export type AddNumbers<Numbers extends readonly number[]> =
+  NumbersToArray<Numbers> extends infer T extends readonly any[]
+    ? T["length"]
+    : never;
+
+export type AddStrings<
+  Strings extends readonly string[],
+  Carry extends string = ""
+> = Strings extends [infer Head extends string, ...infer Tail extends string[]]
+  ? AddStrings<Tail, `${Carry}${Head}`>
+  : Carry;
+
+export type BUILTIN_Arr<Args extends readonly any[]> = Args;
+
+export type BUILTIN_ToString<Args extends readonly any[]> = ToStringInner<
   UnarrayIfOnlyHead<{
-    [Idx in keyof Args]: Args[Idx] extends ASTNode
-      ? ToStringInner<Evaluate<Args[Idx]>>
-      : never;
+    [Idx in keyof Args]: ToStringInner<Args[Idx]>;
   }>
 >;
-// export type BUILTIN_Print<Args extends readonly ASTNode[]>
+
+export type BUILTIN_Add<Args extends readonly any[]> =
+  Args extends readonly string[]
+    ? AddStrings<Args>
+    : Args extends readonly number[]
+    ? AddNumbers<Args>
+    : FnError<`Cannot add operands ${ToStringInner<Args>}`>;
 
 export type SENTINEL_NO_BUILTIN = "__NO_BUILTIN__";
-export type MapBuiltins<Node extends ASTNode> = Node["name"] extends "tostring"
-  ? BUILTIN_ToString<Node["children"]>
-  : Node["name"] extends "arr"
-  ? BUILTIN_ARR<Node["children"]>
-  : SENTINEL_NO_BUILTIN;
+export type MapBuiltins<Node extends ASTNode> =
+  Node["children"] extends infer Children extends readonly ASTNode[]
+    ? {
+        [Idx in keyof Children]: Children[Idx] extends ASTNode
+          ? Evaluate<Children[Idx]>
+          : never;
+      } extends infer Args extends readonly any[]
+      ? Node["name"] extends "tostring"
+        ? BUILTIN_ToString<Args>
+        : Node["name"] extends "arr"
+        ? BUILTIN_Arr<Args>
+        : Node["name"] extends "add"
+        ? BUILTIN_Add<Args>
+        : SENTINEL_NO_BUILTIN
+      : never
+    : never;
 
 export type EvalError<T extends string> = `Eval error: ${T}`;
 
@@ -54,7 +96,7 @@ export type Evaluate<Node extends ASTNode> = Node["type"] extends NodeType.INT
   ? MapBuiltins<Node>
   : EvalError<`Unhandled node type ${Node["type"]}`>;
 
-const input = `5, arr(5000)` as const;
+const input = `add(1,2,3,4,5)` as const;
 const lex_result = null as unknown as Lex<typeof input>;
 const parse_result = null as unknown as Parse<typeof lex_result>;
 const eval_result = null as unknown as Evaluate<typeof parse_result>;