feat: exists

soraLib · May 23, 2022 · 75c5053 · 75c5053
1 parent ea23c46
commit 75c5053
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Showing 2 changed files with 19 additions and 1 deletion.
diff --git a/src/Either.ts b/src/Either.ts
@@ -121,3 +121,15 @@ export const chain = <E2, A, B>(f: (a: A) => Either<E2, B>) => <E1>(ma: Either<E
  */
 export const orElse = <E1, E2, B>(onLeft: (e: E1) => Either<E2, B>) => <A>(ma: Either<E1, A>): Either<E2, A | B> =>
   isLeft(ma) ? onLeft(ma.left) : ma
+
+/**
+ * Returns `false` if `Either` is a `Left`, otherwise returns the predicate result.
+ *
+ * @example
+ *
+ * assert.deepStrictEqual(exists((n: number) => n > 0)(left(0)), false)
+ * assert.deepStrictEqual(exists((n: number) => n > 0)(right(0)), false)
+ * assert.deepStrictEqual(exists((n: number) => n > 0)(right(1)), true)
+ */
+export const exists = <A>(predicate: Predicate<A>) => <E>(ma: Either<E, A>): boolean =>
+  isLeft(ma) ? false : predicate(ma.right)
diff --git a/test/Either.spec.ts b/test/Either.spec.ts
@@ -1,4 +1,4 @@
-import { isLeft, left, right, isRight, map, of, fromPredicate, match, getOrElse, chain, orElse } from '../src/Either'
+import { isLeft, left, right, isRight, map, of, fromPredicate, match, getOrElse, chain, orElse, exists } from '../src/Either'
 
 test('isLeft', () => {
   expect(isLeft(left(0))).toBeTruthy()
@@ -49,3 +49,9 @@ test('orElse', () => {
   expect(orElse((n: number) => right(n + 1))(left(1))).toEqual(right(2))
   expect(orElse((n: number) => right(n + 1))(right(1))).toEqual(right(1))
 })
+
+test('exists', () => {
+  expect(exists((n: number) => n > 0)(left(0))).toBeFalsy()
+  expect(exists((n: number) => n > 0)(right(0))).toBeFalsy()
+  expect(exists((n: number) => n > 0)(right(1))).toBeTruthy()
+})