From 5fdaa70d0af1356652de38f66fccef4bd3088a26 Mon Sep 17 00:00:00 2001
From: Kai Stevenson <kai@kaistevenson.com>
Date: Sun, 2 Nov 2025 19:42:39 -0800
Subject: fn, call

---
 src/lang/core/eval.ts | 123 +++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 102 insertions(+), 21 deletions(-)

(limited to 'src/lang/core/eval.ts')

diff --git a/src/lang/core/eval.ts b/src/lang/core/eval.ts
index 6a25a6c..258999a 100644
--- a/src/lang/core/eval.ts
+++ b/src/lang/core/eval.ts
@@ -3,40 +3,121 @@ import {
   BUILTIN_Arr,
   BUILTIN_Mul,
   BUILTIN_ToString,
+  SBUILTIN_Call,
+  SBUILTIN_Map,
 } from "../builtin";
+import { ToString } from "../util";
 import { ASTNode, NodeType } from "./common";
 import { Lex } from "./lexer";
 import { Parse } from "./parser";
 
+export type GetEvaluatedChildren<
+  Node extends ASTNode,
+  Frame extends StackFrame
+> = Node["children"] extends infer Children extends readonly ASTNode[]
+  ? {
+      [Idx in keyof Children]: Children[Idx] extends ASTNode
+        ? Evaluate<Children[Idx], Frame>
+        : never;
+    }
+  : never;
+
 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 MapBuiltins<
+  Node extends ASTNode,
+  Frame extends StackFrame
+> = GetEvaluatedChildren<Node, Frame> extends infer Args extends readonly any[]
+  ? Node["name"] extends "call"
+    ? SBUILTIN_Call<Node, Frame>
+    : Node["name"] extends "map"
+    ? SBUILTIN_Map<Node, Frame>
+    : 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;
 
 export type EvalError<T extends string> = `Eval error: ${T}`;
 
-export type Evaluate<Node extends ASTNode> = Node["type"] extends NodeType.INT
+export type StackFrame<
+  Bindings extends Record<ASTNode["name"], any> = Record<ASTNode["name"], any>,
+  Parent extends StackFrame | null = any
+> = {
+  bindings: Bindings;
+  parent: Parent;
+};
+
+export type EmptyStackFrame = StackFrame<{}, null>;
+
+export type WithPushedBindings<
+  OldFrame extends StackFrame,
+  Bindings extends StackFrame["bindings"]
+> = StackFrame<Bindings, OldFrame>;
+
+export type FindInStack<
+  Frame extends StackFrame,
+  NameToFind
+> = NameToFind extends keyof Frame["bindings"]
+  ? Frame["bindings"][NameToFind]
+  : Frame["parent"] extends null
+  ? EvalError<`Can't find name "${ToString<NameToFind>}" on the stack`>
+  : FindInStack<Frame["parent"], NameToFind>;
+
+export type MapOnStack<
+  Node extends ASTNode,
+  Frame extends StackFrame
+> = FindInStack<Frame, Node["name"]>;
+
+export type FnPrim<
+  Args extends readonly ASTNode[] = readonly ASTNode[],
+  Fn extends ASTNode = ASTNode
+> = { args: Args; fn: Fn };
+
+// Can support multiple args, just need to make the last arg be the fn
+export type HandleFn<Node extends ASTNode> = Node["children"] extends [
+  infer Arg extends ASTNode,
+  infer Fn extends ASTNode
+]
+  ? FnPrim<[Arg], Fn>
+  : never;
+
+type MapZip<T extends readonly ASTNode[], U extends readonly PropertyKey[]> = {
+  [Idx in Exclude<
+    keyof T,
+    keyof any[]
+  > as T[Idx] extends infer Node extends ASTNode
+    ? Node["name"]
+    : never]: Idx extends keyof U ? U[Idx] : never;
+};
+
+export type CallFn<
+  Fn extends FnPrim,
+  Values extends readonly any[],
+  Frame extends StackFrame
+> = Evaluate<Fn["fn"], StackFrame<MapZip<Fn["args"], Values>, Frame>>;
+
+export type Evaluate<
+  Node extends ASTNode,
+  Frame extends StackFrame = EmptyStackFrame
+> = Node["type"] extends NodeType.INT
   ? Node["value"]
   : Node["type"] extends NodeType.EXT
-  ? MapBuiltins<Node>
+  ? // special builtin
+    Node["name"] extends "fn"
+    ? HandleFn<Node>
+    : MapBuiltins<Node, Frame> extends infer BI
+    ? BI extends SENTINEL_NO_BUILTIN
+      ? MapOnStack<Node, Frame>
+      : BI
+    : never
   : EvalError<`Unhandled node type ${Node["type"]}`>;
 
-const input = `` as const;
+const input = `map(arr(5,5,5), fn(n, add(n, 1)))` 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>;
-- 
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