From 1b629aaae4b2cf131fe1d5aee44880f7c2805405 Mon Sep 17 00:00:00 2001
From: Brandon Lucas <blu@blu.cx>
Date: Fri, 20 Feb 2026 19:21:26 -0500
Subject: [PATCH] feat: add 10 missing List operations to JS backend

Add find, findIndex, any, all, zip, flatten, contains, take, drop,
and forEach to the JS backend's emit_list_operation function. These
operations previously worked in the interpreter and C backend but
caused "Unknown List operation" errors when compiled to JS.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
---
 src/codegen/js_backend.rs | 61 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 61 insertions(+)

diff --git a/src/codegen/js_backend.rs b/src/codegen/js_backend.rs
index 283c298..cbd119d 100644
--- a/src/codegen/js_backend.rs
+++ b/src/codegen/js_backend.rs
@@ -1835,6 +1835,67 @@ impl JsBackend {
                 let func = self.emit_expr(&args[1])?;
                 Ok(format!("[...{}].sort({})", list, func))
             }
+            "find" => {
+                let list = self.emit_expr(&args[0])?;
+                let pred = self.emit_expr(&args[1])?;
+                Ok(format!(
+                    "((__l) => {{ const __r = __l.find({}); return __r !== undefined ? Lux.Some(__r) : Lux.None(); }})({})",
+                    pred, list
+                ))
+            }
+            "findIndex" => {
+                let list = self.emit_expr(&args[0])?;
+                let pred = self.emit_expr(&args[1])?;
+                Ok(format!(
+                    "((__l) => {{ const __i = __l.findIndex({}); return __i !== -1 ? Lux.Some(__i) : Lux.None(); }})({})",
+                    pred, list
+                ))
+            }
+            "any" => {
+                let list = self.emit_expr(&args[0])?;
+                let pred = self.emit_expr(&args[1])?;
+                Ok(format!("{}.some({})", list, pred))
+            }
+            "all" => {
+                let list = self.emit_expr(&args[0])?;
+                let pred = self.emit_expr(&args[1])?;
+                Ok(format!("{}.every({})", list, pred))
+            }
+            "zip" => {
+                let list1 = self.emit_expr(&args[0])?;
+                let list2 = self.emit_expr(&args[1])?;
+                Ok(format!(
+                    "((__a, __b) => __a.slice(0, Math.min(__a.length, __b.length)).map((__x, __i) => [__x, __b[__i]]))({})",
+                    format!("{}, {}", list1, list2)
+                ))
+            }
+            "flatten" => {
+                let list = self.emit_expr(&args[0])?;
+                Ok(format!("{}.flat()", list))
+            }
+            "contains" => {
+                let list = self.emit_expr(&args[0])?;
+                let elem = self.emit_expr(&args[1])?;
+                Ok(format!(
+                    "{}.some(__x => JSON.stringify(__x) === JSON.stringify({}))",
+                    list, elem
+                ))
+            }
+            "take" => {
+                let list = self.emit_expr(&args[0])?;
+                let n = self.emit_expr(&args[1])?;
+                Ok(format!("{}.slice(0, Math.max(0, {}))", list, n))
+            }
+            "drop" => {
+                let list = self.emit_expr(&args[0])?;
+                let n = self.emit_expr(&args[1])?;
+                Ok(format!("{}.slice(Math.max(0, {}))", list, n))
+            }
+            "forEach" => {
+                let list = self.emit_expr(&args[0])?;
+                let func = self.emit_expr(&args[1])?;
+                Ok(format!("({}.forEach({}), undefined)", list, func))
+            }
             _ => Err(JsGenError {
                 message: format!("Unknown List operation: {}", operation),
                 span: None,