Optional: add missing fromNullable combinator, closes #133

Author: gcanti

CHANGELOG.md

@@ -19,6 +19,8 @@ high state of flux, you're at risk of it changing without notice.
   - `Prism`
     - (\*) remove `fromSome` constructor (@gcanti)
     - (\*) change `fromNullable` signature (@gcanti)
+  - `Optional`
+    - add missing `fromNullable` combinator, closes #133 (@gcanti)
 
 (\*) breaking change
 

docs/modules/Optional.ts.md

@@ -37,6 +37,7 @@ Added in v2.3.0
   - [component](#component)
   - [filter](#filter)
   - [findFirst](#findfirst)
+  - [fromNullable](#fromnullable)
   - [index](#index)
   - [key](#key)
   - [left](#left)
@@ -126,6 +127,18 @@ export declare const findFirst: <A>(predicate: Predicate<A>) => <S>(sa: Optional
 
 Added in v2.3.2
 
+## fromNullable
+
+Return an `Optional` from a `Optional` focused on a nullable value
+
+**Signature**
+
+```ts
+export declare const fromNullable: <S, A>(sa: Optional<S, A>) => Optional<S, NonNullable<A>>
+```
+
+Added in v2.3.3
+
 ## index
 
 Return a `Optional` from a `Optional` focused on a `ReadonlyArray`

src/Optional.ts

@@ -100,6 +100,16 @@ export const modifyOption: <A>(f: (a: A) => A) => <S>(optional: Optional<S, A>)
  */
 export const modify: <A>(f: (a: A) => A) => <S>(optional: Optional<S, A>) => (s: S) => S = _.optionalModify
 
+/**
+ * Return an `Optional` from a `Optional` focused on a nullable value
+ *
+ * @category combinators
+ * @since 2.3.3
+ */
+export const fromNullable: <S, A>(sa: Optional<S, A>) => Optional<S, NonNullable<A>> =
+  /*#__PURE__*/
+  compose(_.prismAsOptional(_.prismFromNullable()))
+
 /**
  * @category combinators
  * @since 2.3.0

src/Prism.ts

@@ -120,6 +120,12 @@ export const composeOptional = <A, B>(ab: Optional<A, B>) => <S>(sa: Prism<S, A>
 // combinators
 // -------------------------------------------------------------------------------------
 
+/**
+ * @category combinators
+ * @since 2.3.0
+ */
+export const set: <A>(a: A) => <S>(sa: Prism<S, A>) => (s: S) => S = _.prismSet
+
 /**
  * @category combinators
  * @since 2.3.0
@@ -142,16 +148,6 @@ export const fromNullable: <S, A>(sa: Prism<S, A>) => Prism<S, NonNullable<A>> =
   /*#__PURE__*/
   compose(_.prismFromNullable())
 
-/**
- * @category combinators
- * @since 2.3.0
- */
-export const set: <A>(a: A) => <S>(sa: Prism<S, A>) => (s: S) => S = _.prismSet
-
-// -------------------------------------------------------------------------------------
-// combinators
-// -------------------------------------------------------------------------------------
-
 /**
  * @category combinators
  * @since 2.3.0

test/Optional.ts

@@ -142,4 +142,17 @@ describe('Optional', () => {
     )
     assert.deepStrictEqual(modify(O.some({ a: ['a'] })), O.some({ a: ['A'] }))
   })
+
+  it('fromNullable', () => {
+    interface S {
+      a?: number
+    }
+    const sa = pipe(_.id<S>(), _.prop('a'), _.fromNullable)
+    assert.deepStrictEqual(sa.getOption({}), O.none)
+    assert.deepStrictEqual(sa.getOption({ a: undefined }), O.none)
+    assert.deepStrictEqual(sa.getOption({ a: 1 }), O.some(1))
+    assert.deepStrictEqual(sa.set(2)({}), {})
+    assert.deepStrictEqual(sa.set(2)({ a: undefined }), { a: undefined })
+    assert.deepStrictEqual(sa.set(2)({ a: 1 }), { a: 2 })
+  })
 })