Fix

packages/effect-fc/src/Lens.ts

@@ -79,7 +79,9 @@ export const map = <A, ER, RR, EW, RW, B>(
         (b: B): (parent: A) => A
     },
 ): Lens<B, ER, RR, EW, RW> => {
-    const setF =
+    const setF = (parent: A, b: B) => set.length >= 2
+        ? (set as (parent: A, b: B) => A)(parent, b)
+        : (set as (b: B) => (parent: A) => A)(b)(parent)
 
     return make({
         get: Effect.map(self.get, get),
@@ -87,7 +89,7 @@ export const map = <A, ER, RR, EW, RW, B>(
         modify: <C, E1 = never, R1 = never>(
             f: (b: B) => Effect.Effect<readonly [C, B], E1, R1>
         ) => self.modify((a: A) =>
-            Effect.flatMap(f(get(a)), ([c, next]) => Effect.succeed([c, set(a, next)] as const))
+            Effect.flatMap(f(get(a)), ([c, next]) => Effect.succeed([c, setF(a, next)] as const))
         ),
     })
 }