From 07a74315e1d85c97ddf5c9eac26ef2036ab9b3e3 Mon Sep 17 00:00:00 2001
From: themodernhakr <ehrumsey@gmail.com>
Date: Mon, 9 Jun 2025 00:56:38 -0500
Subject: [PATCH] Add bindL to DoEither

---
 src/either.ts | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/src/either.ts b/src/either.ts
index 3e3e03c..c6977eb 100644
--- a/src/either.ts
+++ b/src/either.ts
@@ -106,6 +106,26 @@ export class DoEither<T extends Record<string, unknown>, E> {
     return new DoEither(newEither)
   }
 
+  /**
+   * Binds a new value to the scope using a lazily evaluated Either
+   * @typeParam K - The key to bind to
+   * @typeParam A - The type of the value to bind
+   * @param key - The property name to bind to
+   * @param f - Function returning the Either value to bind (receives current scope)
+   * @returns A new DoEither instance with the extended scope
+   */
+  bindL<K extends string, A>(
+    key: K,
+    f: (scope: T) => Either<A, E>,
+  ): DoEither<T & Record<K, A>, E> {
+    const newEither = eitherChain<T, T & Record<K, A>, E>((scope: T) =>
+      eitherMap<A, T & Record<K, A>, E>((a: A) => ({...scope, [key]: a}))(
+        f(scope),
+      )
+    )(this.either)
+    return new DoEither(newEither)
+  }
+
   /**
    * Returns the final result from the scope
    * @typeParam B - The return type