3 files changed, 56 insertions, 0 deletions
diff --git a/src/lang/js-lang/builtin/sbuiltin.ts b/src/lang/js-lang/builtin/sbuiltin.ts
index 013854c..7d9b851 100644
--- a/src/lang/js-lang/builtin/sbuiltin.ts
+++ b/src/lang/js-lang/builtin/sbuiltin.ts
@@ -40,6 +40,30 @@ export const V_SBUILTIN_Map: SBUILTIN = (node, frame) => {
   return values.map((v, i) => callFn(fn, [v, i], frame));
 };
 
+export const V_SBUILTIN_Reduce: SBUILTIN = (node, frame) => {
+  const children = getEvaluatedChildren(node, frame);
+  const fn = children[1] as FnPrim | undefined;
+  const acc = children[2];
+
+  if (!fn?.fn) {
+    throw new Error(
+      `Invalid params for reduce: ${JSON.stringify(children, undefined, 2)}`
+    );
+  }
+
+  const values = children[0];
+
+  if (!Array.isArray(values)) {
+    // add to ts
+    throw new Error(`Can't reduce non-array value: ${values}`);
+  }
+
+  return values.reduce(
+    (acc, cur, idx) => callFn(fn, [acc, cur, idx], frame),
+    acc
+  );
+};
+
 export const V_SBUILTIN_IfElse: SBUILTIN = (node, frame) => {
   const children = node.children;
 
@@ -59,5 +83,6 @@ export const V_SBUILTIN_IfElse: SBUILTIN = (node, frame) => {
 export const nameToSBUILTIN: Record<string, SBUILTIN> = {
   call: V_SBUILTIN_Call,
   map: V_SBUILTIN_Map,
+  reduce: V_SBUILTIN_Reduce,
   "?": V_SBUILTIN_IfElse,
 };
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"