From 22672c98dce5f97a0eaeb63a2d5610a73954cb98 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Julien=20Valverd=C3=A9?= <julien.valverde@mailo.com>
Date: Tue, 31 Mar 2026 18:47:51 +0200
Subject: [PATCH] Add Form.focusTupleAt

---
 packages/effect-fc/src/Form.ts | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/packages/effect-fc/src/Form.ts b/packages/effect-fc/src/Form.ts
index 564d8f4..b8206b6 100644
--- a/packages/effect-fc/src/Form.ts
+++ b/packages/effect-fc/src/Form.ts
@@ -298,6 +298,32 @@ export const focusArrayAt: {
     )
 })
 
+export const focusTupleAt: {
+    <P extends readonly PropertyKey[], A extends readonly [any, ...any[]], I extends readonly [any, ...any[]], ER, EW, K extends number>(
+        self: Form<P, A, I, ER, EW>,
+        index: K,
+    ): Form<readonly [...P, number], A[number], I[number], ER, EW>
+    <P extends readonly PropertyKey[], A extends readonly [any, ...any[]], I extends readonly [any, ...any[]], ER, EW, K extends number>(
+        index: K,
+    ): (self: Form<P, A, I, ER, EW>) => Form<readonly [...P, number], A[number], I[number], ER, EW>
+} = Function.dual(2, <P extends readonly PropertyKey[], A extends readonly [any, ...any[]], I extends readonly [any, ...any[]], ER, EW, K extends number>(
+    self: Form<P, A, I, ER, EW>,
+    index: K,
+): Form<readonly [...P, K], A[number], I[number], ER, EW> => {
+    const form = self as FormImpl<P, A, I, ER, EW>
+    const path = [...form.path, index] as const
+
+    return new FormImpl(
+        path,
+        Subscribable.mapOption(form.value, Array.unsafeGet(index)),
+        Lens.focusTupleAt(form.encodedValue, index),
+        Subscribable.map(form.issues, issues => filterIssuesByPath(issues, path)),
+        form.isValidating,
+        form.canSubmit,
+        form.isSubmitting,
+    )
+})
+
 
 export namespace useInput {
     export interface Options {