From 190f85ff1ac23f952a7b4960638fee79495e249a Mon Sep 17 00:00:00 2001
From: Kai Stevenson <kai@kaistevenson.com>
Date: Sun, 9 Nov 2025 21:52:06 -0800
Subject: filter

---
 src/lang/ts-lang/builtin/sbuiltin.ts | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

(limited to 'src/lang/ts-lang/builtin/sbuiltin.ts')

diff --git a/src/lang/ts-lang/builtin/sbuiltin.ts b/src/lang/ts-lang/builtin/sbuiltin.ts
index 38b4256..f089aea 100644
--- a/src/lang/ts-lang/builtin/sbuiltin.ts
+++ b/src/lang/ts-lang/builtin/sbuiltin.ts
@@ -70,6 +70,35 @@ export type SBUILTIN_Reduce<
       GetEvaluatedChildren<Node, Frame, Callstack>
     >}`>;
 
+type Filter<
+  Arr extends readonly any[],
+  Fn extends FnPrim,
+  Collected extends readonly any[] = [],
+  IdxLen extends readonly any[] = readonly []
+> = Arr extends [infer Head, ...infer Tail]
+  ? Filter<
+      Tail,
+      Fn,
+      CallFn<Fn, [Head, IdxLen["length"]]> extends true
+        ? [...Collected, Head]
+        : Collected,
+      [...IdxLen, any]
+    >
+  : Collected;
+
+export type SBUILTIN_Filter<
+  Node extends ASTNode,
+  Frame extends StackFrame,
+  Callstack extends readonly string[]
+> = GetEvaluatedChildren<Node, Frame, Callstack> extends [
+  infer Arr extends readonly any[],
+  infer Fn extends FnPrim
+]
+  ? Filter<Arr, Fn>
+  : EvalError<`Invalid params for filter: ${ToString<
+      GetEvaluatedChildren<Node, Frame, Callstack>
+    >}`>;
+
 export type SBUILTIN_IfElse<
   Node extends ASTNode,
   Frame extends StackFrame,
-- 
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