1 files changed, 42 insertions, 0 deletions
diff --git a/src/lang/core/eval.ts b/src/lang/core/eval.ts
new file mode 100644
index 0000000..6a25a6c
--- /dev/null
+++ b/src/lang/core/eval.ts
@@ -0,0 +1,42 @@
+import {
+  BUILTIN_Add,
+  BUILTIN_Arr,
+  BUILTIN_Mul,
+  BUILTIN_ToString,
+} from "../builtin";
+import { ASTNode, NodeType } from "./common";
+import { Lex } from "./lexer";
+import { Parse } from "./parser";
+
+export type SENTINEL_NO_BUILTIN = "__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>
+        : Node["name"] extends "mul"
+        ? BUILTIN_Mul<Args>
+        : SENTINEL_NO_BUILTIN
+      : never
+    : never;
+
+export type EvalError<T extends string> = `Eval error: ${T}`;
+
+export type Evaluate<Node extends ASTNode> = Node["type"] extends NodeType.INT
+  ? Node["value"]
+  : Node["type"] extends NodeType.EXT
+  ? MapBuiltins<Node>
+  : EvalError<`Unhandled node type ${Node["type"]}`>;
+
+const input = `` 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>;