4 files changed, 54 insertions, 1 deletions
diff --git a/src/lang/js-lang/builtin/sbuiltin.ts b/src/lang/js-lang/builtin/sbuiltin.ts
index 7d9b851..60cd117 100644
--- a/src/lang/js-lang/builtin/sbuiltin.ts
+++ b/src/lang/js-lang/builtin/sbuiltin.ts
@@ -64,6 +64,26 @@ export const V_SBUILTIN_Reduce: SBUILTIN = (node, frame) => {
   );
 };
 
+export const V_SBUILTIN_Filter: SBUILTIN = (node, frame) => {
+  const children = getEvaluatedChildren(node, frame);
+  const fn = children[1] as FnPrim | undefined;
+
+  if (!fn?.fn) {
+    throw new Error(
+      `Invalid params for filter: ${JSON.stringify(children, undefined, 2)}`
+    );
+  }
+
+  const values = children[0];
+
+  if (!Array.isArray(values)) {
+    // add to ts
+    throw new Error(`Can't filter non-array value: ${values}`);
+  }
+
+  return values.filter((v, idx) => callFn(fn, [v, idx], frame) === true);
+};
+
 export const V_SBUILTIN_IfElse: SBUILTIN = (node, frame) => {
   const children = node.children;
 
@@ -84,5 +104,6 @@ export const nameToSBUILTIN: Record<string, SBUILTIN> = {
   call: V_SBUILTIN_Call,
   map: V_SBUILTIN_Map,
   reduce: V_SBUILTIN_Reduce,
+  filter: V_SBUILTIN_Filter,
   "?": V_SBUILTIN_IfElse,
 };
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: ${ToString<
+      GetEvaluatedChildren<Node, Frame, Callstack>
+    >}`>;
+
 export type SBUILTIN_IfElse<
   Node extends ASTNode,
   Frame extends StackFrame,
diff --git a/src/lang/ts-lang/core/eval.ts b/src/lang/ts-lang/core/eval.ts
index bef0ef8..b937c2e 100644
--- a/src/lang/ts-lang/core/eval.ts
+++ b/src/lang/ts-lang/core/eval.ts
@@ -6,6 +6,7 @@ import {
   BUILTIN_Sub,
   BUILTIN_ToString,
   SBUILTIN_Call,
+  SBUILTIN_Filter,
   SBUILTIN_IfElse,
   SBUILTIN_Map,
   SBUILTIN_Reduce,
@@ -37,6 +38,8 @@ export type MapBuiltins<
     ? SBUILTIN_Map<Node, Frame, Callstack>
     : Node["name"] extends "reduce"
     ? SBUILTIN_Reduce<Node, Frame, Callstack>
+    : Node["name"] extends "filter"
+    ? SBUILTIN_Filter<Node, Frame, Callstack>
     : Node["name"] extends "?"
     ? SBUILTIN_IfElse<Node, Frame, Callstack>
     : Node["name"] extends "tostring"
diff --git a/src/lang/ts-lang/core/lexer.ts b/src/lang/ts-lang/core/lexer.ts
index bcd5785..43dc3e5 100644
--- a/src/lang/ts-lang/core/lexer.ts
+++ b/src/lang/ts-lang/core/lexer.ts
@@ -36,7 +36,7 @@ export type IsClose<T> = T extends `${TokenType.CLOSE_PAREN}` ? true : false;
 export type ChunkedLex<
   Ctx extends LexerCtx,
   Depth extends any[] = []
-> = Depth["length"] extends 50
+> = Depth["length"] extends 25
   ? Ctx & {
       endChunk: true;
     }