Flip the arguments of a curried function

docs/modules/function.ts.md

@@ -306,14 +306,25 @@ Added in v2.0.0
 
 ## flip
 
-Flips the order of the arguments of a function of two arguments.
+Flips the arguments of a curried function.
 
 **Signature**
 
 ```ts
+export declare function flip<A, B, C>(f: (a: A) => (b: B) => C): (b: B) => (a: A) => C
 export declare function flip<A, B, C>(f: (a: A, b: B) => C): (b: B, a: A) => C
 ```
 
+**Example**
+
+```ts
+import { flip } from 'fp-ts/function'
+
+const f = (a: number) => (b: string) => a - b.length
+
+assert.strictEqual(flip(f)('aaa')(2), -1)
+```
+
 Added in v2.0.0
 
 ## flow

src/function.ts

@@ -194,12 +194,28 @@ export const constUndefined: Lazy<undefined> = /*#__PURE__*/ constant(undefined)
 export const constVoid: Lazy<void> = constUndefined
 
 /**
- * Flips the order of the arguments of a function of two arguments.
+ * Flips the arguments of a curried function.
+ *
+ * @example
+ * import { flip } from 'fp-ts/function'
+ *
+ * const f = (a: number) => (b: string) => a - b.length
+ *
+ * assert.strictEqual(flip(f)('aaa')(2), -1)
  *
  * @since 2.0.0
  */
-export function flip<A, B, C>(f: (a: A, b: B) => C): (b: B, a: A) => C {
-  return (b, a) => f(a, b)
+export function flip<A, B, C>(f: (a: A) => (b: B) => C): (b: B) => (a: A) => C
+/** @deprecated */
+export function flip<A, B, C>(f: (a: A, b: B) => C): (b: B, a: A) => C
+export function flip(f: Function): Function {
+  return (...args: Array<any>) => {
+    if (args.length > 1) {
+      return f(args[1], args[0])
+    }
+
+    return (a: any) => f(a)(args[0])
+  }
 }
 
 /**

test/function.ts

@@ -10,9 +10,13 @@ const f = (n: number) => n + 1
 const g = (n: number) => n * 2
 
 describe('function', () => {
-  it('flip', () => {
-    const f = (a: number, b: string) => a - b.length
-    U.deepStrictEqual(_.flip(f)('aaa', 2), -1)
+  test('flip', () => {
+    const f1 = (a: number) => (b: string) => a - b.length
+    const f2 = (a: number, b: string) => a - b.length
+
+    U.deepStrictEqual(_.flip(f1)('aaa')(2), -1)
+    // eslint-disable-next-line deprecation/deprecation
+    U.deepStrictEqual(_.flip(f2)('aaa', 2), -1)
   })
 
   it('not', () => {