fromNullable now uses NonNullable in its return type, fixes #1004

CHANGELOG.md

@@ -14,6 +14,11 @@
 **Note**: Gaps between patch versions are faulty/broken releases. **Note**: A feature tagged as Experimental is in a
 high state of flux, you're at risk of it changing without notice.
 
+# 2.1.2
+
+- **Bug Fix**
+  - `fromNullable` now uses `NonNullable` in its return type, fixes #1004 (@gcanti)
+
 # 2.1.1
 
 - **Bug Fix**

docs/modules/Either.ts.md

@@ -246,7 +246,7 @@ the provided default as a `Left`
 **Signature**
 
 ```ts
-export function fromNullable<E>(e: E): <A>(a: A | null | undefined) => Either<E, A> { ... }
+export function fromNullable<E>(e: E): <A>(a: A) => Either<E, NonNullable<A>> { ... }
 ```
 
 **Example**

docs/modules/Option.ts.md

@@ -275,7 +275,7 @@ returns the value wrapped in a `Some`
 **Signature**
 
 ```ts
-export function fromNullable<A>(a: A | null | undefined): Option<A> { ... }
+export function fromNullable<A>(a: A): Option<NonNullable<A>> { ... }
 ```
 
 **Example**

dtslint/ts3.5/index.ts

@@ -167,6 +167,31 @@ type C = A | B
 // $ExpectError
 O.getRefinement<C, A>(c => (c.type === 'B' ? O.some(c) : O.none))
 
+// fromNullable
+
+declare const fromNullableTest1: number | null | undefined
+O.fromNullable(fromNullableTest1) // $ExpectType Option<number>
+
+interface fromNullableTest2 {
+  foo: number | undefined
+}
+declare const fromNullableTest3: <Key extends keyof fromNullableTest2>(key: Key) => fromNullableTest2[Key]
+// $ExpectType Option<number>
+Fu.flow(
+  fromNullableTest3,
+  O.fromNullable
+)('foo')
+
+//
+// Either
+//
+
+// $ExpectType Either<string, number>
+Fu.flow(
+  fromNullableTest3,
+  E.fromNullable('error')
+)('foo')
+
 //
 // HKT
 //

package.json

@@ -1,6 +1,6 @@
 {
   "name": "fp-ts",
-  "version": "2.1.1",
+  "version": "2.1.2",
   "description": "Functional programming in TypeScript",
   "files": [
     "lib",

src/Either.ts

@@ -118,8 +118,8 @@ export function right<E = never, A = never>(a: A): Either<E, A> {
  *
  * @since 2.0.0
  */
-export function fromNullable<E>(e: E): <A>(a: A | null | undefined) => Either<E, A> {
-  return a => (a == null ? left(e) : right(a))
+export function fromNullable<E>(e: E): <A>(a: A) => Either<E, NonNullable<A>> {
+  return <A>(a: A) => (a == null ? left(e) : right(a as NonNullable<A>))
 }
 
 /**

src/Option.ts

@@ -160,8 +160,8 @@ export function fold<A, B>(onNone: () => B, onSome: (a: A) => B): (ma: Option<A>
  *
  * @since 2.0.0
  */
-export function fromNullable<A>(a: A | null | undefined): Option<A> {
-  return a == null ? none : some(a)
+export function fromNullable<A>(a: A): Option<NonNullable<A>> {
+  return a == null ? none : some(a as NonNullable<A>)
 }
 
 /**