Covariant: flip flap

fp-ts · Feb 7, 2023 · 9569811 · 9569811
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diff --git a/.changeset/poor-crabs-drum.md b/.changeset/poor-crabs-drum.md
@@ -0,0 +1,5 @@
+---
+"@fp-ts/core": minor
+---
+
+Covariant: flip flap
diff --git a/docs/modules/Either.ts.md b/docs/modules/Either.ts.md
@@ -1117,7 +1117,7 @@ Added in v1.0.0
 **Signature**
 
 ```ts
-export declare const flap: <A>(a: A) => <E, B>(self: Either<E, (a: A) => B>) => Either<E, B>
+export declare const flap: <E, A, B>(self: Either<E, (a: A) => B>) => (a: A) => Either<E, B>
 ```
 
 Added in v1.0.0

diff --git a/docs/modules/Option.ts.md b/docs/modules/Option.ts.md
@@ -1173,7 +1173,7 @@ Added in v1.0.0
 **Signature**
 
 ```ts
-export declare const flap: <A>(a: A) => <B>(fab: Option<(a: A) => B>) => Option<B>
+export declare const flap: <A, B>(self: Option<(a: A) => B>) => (a: A) => Option<B>
 ```
 
 Added in v1.0.0

diff --git a/docs/modules/ReadonlyArray.ts.md b/docs/modules/ReadonlyArray.ts.md
@@ -1441,7 +1441,7 @@ Added in v1.0.0
 **Signature**
 
 ```ts
-export declare const flap: <A>(a: A) => <B>(self: readonly ((a: A) => B)[]) => B[]
+export declare const flap: <A, B>(self: readonly ((a: A) => B)[]) => (a: A) => B[]
 ```
 
 Added in v1.0.0

diff --git a/docs/modules/These.ts.md b/docs/modules/These.ts.md
@@ -1213,7 +1213,7 @@ Added in v1.0.0
 **Signature**
 
 ```ts
-export declare const flap: <A>(a: A) => <E, B>(self: any) => any
+export declare const flap: <E, A, B>(self: any) => (a: A) => any
 ```
 
 Added in v1.0.0

diff --git a/docs/modules/typeclass/Covariant.ts.md b/docs/modules/typeclass/Covariant.ts.md
@@ -66,7 +66,7 @@ Added in v1.0.0
 **Signature**
 
 ```ts
-export declare const flap: <F extends any>(F: Covariant<F>) => <A>(a: A) => <R, O, E, B>(self: any) => any
+export declare const flap: <F extends any>(F: Covariant<F>) => <R, O, E, A, B>(self: any) => (a: A) => any
 ```
 
 Added in v1.0.0

diff --git a/src/Either.ts b/src/Either.ts
@@ -160,10 +160,8 @@ export const bindTo: <N extends string>(
  * @category mapping
  * @since 1.0.0
  */
-export const flap: <A>(a: A) => <E, B>(self: Either<E, (a: A) => B>) => Either<E, B> = covariant
-  .flap(
-    Covariant
-  )
+export const flap: <E, A, B>(self: Either<E, (a: A) => B>) => (a: A) => Either<E, B> = covariant
+  .flap(Covariant)
 
 /**
  * Maps the Right value of this effect to the specified constant value.

diff --git a/src/Option.ts b/src/Option.ts
@@ -515,9 +515,8 @@ export {
  * @category mapping
  * @since 1.0.0
  */
-export const flap: <A>(a: A) => <B>(fab: Option<(a: A) => B>) => Option<B> = covariant.flap(
-  Covariant
-)
+export const flap: <A, B>(self: Option<(a: A) => B>) => (a: A) => Option<B> = covariant
+  .flap(Covariant)
 
 /**
  * Maps the `Some` value of this option to the specified constant value.

diff --git a/src/ReadonlyArray.ts b/src/ReadonlyArray.ts
@@ -1317,9 +1317,9 @@ export {
  * @category mapping
  * @since 1.0.0
  */
-export const flap: <A>(a: A) => <B>(
-  self: ReadonlyArray<(a: A) => B>
-) => Array<B> = covariant.flap(Covariant) as any
+export const flap: <A, B>(self: ReadonlyArray<(a: A) => B>) => (a: A) => Array<B> = covariant.flap(
+  Covariant
+) as any
 
 /**
  * Maps the success value of this effect to the specified constant value.

diff --git a/src/These.ts b/src/These.ts
@@ -634,10 +634,8 @@ export const bindTo: <N extends string>(
  * @category mapping
  * @since 1.0.0
  */
-export const flap: <A>(a: A) => <E, B>(self: These<E, (a: A) => B>) => These<E, B> = covariant
-  .flap(
-    Covariant
-  )
+export const flap: <E, A, B>(self: These<E, (a: A) => B>) => (a: A) => These<E, B> = covariant
+  .flap(Covariant)
 
 /**
  * Maps the right value of this effect to the specified constant value.

diff --git a/src/typeclass/Covariant.ts b/src/typeclass/Covariant.ts
@@ -1,6 +1,7 @@
 /**
  * @since 1.0.0
  */
+import { pipe } from "@fp-ts/core/Function"
 import type { Kind, TypeLambda } from "@fp-ts/core/HKT"
 import type { Invariant } from "@fp-ts/core/typeclass/Invariant"
 
@@ -50,8 +51,8 @@ export const make = <F extends TypeLambda>(map: Covariant<F>["map"]): Covariant<
  * @since 1.0.0
  */
 export const flap = <F extends TypeLambda>(F: Covariant<F>) =>
-  <A>(a: A): (<R, O, E, B>(self: Kind<F, R, O, E, (a: A) => B>) => Kind<F, R, O, E, B>) =>
-    F.map(f => f(a))
+  <R, O, E, A, B>(self: Kind<F, R, O, E, (a: A) => B>) =>
+    (a: A): Kind<F, R, O, E, B> => pipe(self, F.map(f => f(a)))
 
 /**
  * @category mapping

diff --git a/test/typeclass/Covariant.ts b/test/typeclass/Covariant.ts
@@ -21,8 +21,8 @@ describe("Covariant", () => {
 
   it("flap", () => {
     const flap = _.flap(O.Covariant)
-    U.deepStrictEqual(pipe(O.none(), flap(1)), O.none())
-    U.deepStrictEqual(pipe(O.some(U.double), flap(1)), O.some(2))
+    U.deepStrictEqual(pipe(1, flap(O.none())), O.none())
+    U.deepStrictEqual(pipe(1, flap(O.some(U.double))), O.some(2))
   })
 
   it("as", () => {