From 413eaa284e164143c5416cdce5a1de0f9f992409 Mon Sep 17 00:00:00 2001
From: Kai Stevenson <kai@kaistevenson.com>
Date: Sun, 9 Nov 2025 21:08:12 -0800
Subject: map + reduce

---
 src/lang/ts-lang/builtin/sbuiltin.ts | 28 ++++++++++++++++++++++++++++
 src/lang/ts-lang/core/eval.ts        |  3 +++
 2 files changed, 31 insertions(+)

(limited to 'src/lang/ts-lang')

diff --git a/src/lang/ts-lang/builtin/sbuiltin.ts b/src/lang/ts-lang/builtin/sbuiltin.ts
index c92fd6a..38b4256 100644
--- a/src/lang/ts-lang/builtin/sbuiltin.ts
+++ b/src/lang/ts-lang/builtin/sbuiltin.ts
@@ -42,6 +42,34 @@ export type SBUILTIN_Map<
       GetEvaluatedChildren<Node, Frame, Callstack>
     >}`>;
 
+type Reduce<
+  Arr extends readonly any[],
+  Fn extends FnPrim,
+  Acc,
+  IdxLen extends readonly any[] = readonly []
+> = Arr extends [infer Head, ...infer Tail]
+  ? Reduce<
+      Tail,
+      Fn,
+      CallFn<Fn, [Acc, Head, IdxLen["length"]]>,
+      [...IdxLen, any]
+    >
+  : Acc;
+
+export type SBUILTIN_Reduce<
+  Node extends ASTNode,
+  Frame extends StackFrame,
+  Callstack extends readonly string[]
+> = GetEvaluatedChildren<Node, Frame, Callstack> extends [
+  infer Arr extends readonly any[],
+  infer Fn extends FnPrim,
+  infer Acc
+]
+  ? Reduce<Arr, Fn, Acc>
+  : EvalError<`Invalid params for reduce: ${ToString<
+      GetEvaluatedChildren<Node, Frame, Callstack>
+    >}`>;
+
 export type SBUILTIN_IfElse<
   Node extends ASTNode,
   Frame extends StackFrame,
diff --git a/src/lang/ts-lang/core/eval.ts b/src/lang/ts-lang/core/eval.ts
index ebc58e7..bef0ef8 100644
--- a/src/lang/ts-lang/core/eval.ts
+++ b/src/lang/ts-lang/core/eval.ts
@@ -8,6 +8,7 @@ import {
   SBUILTIN_Call,
   SBUILTIN_IfElse,
   SBUILTIN_Map,
+  SBUILTIN_Reduce,
 } from "../builtin";
 import { ToString } from "../util";
 import {
@@ -34,6 +35,8 @@ export type MapBuiltins<
     ? SBUILTIN_Call<Node, Frame, Callstack>
     : Node["name"] extends "map"
     ? SBUILTIN_Map<Node, Frame, Callstack>
+    : Node["name"] extends "reduce"
+    ? SBUILTIN_Reduce<Node, Frame, Callstack>
     : Node["name"] extends "?"
     ? SBUILTIN_IfElse<Node, Frame, Callstack>
     : Node["name"] extends "tostring"
-- 
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