feat(maybe): introduce maybeToPromise

src/monads/maybe.ts

@@ -45,3 +45,9 @@ export const maybe = <T>(value?: T): IMaybe<NonNullable<T>> => {
     filter: filter(value)
   }
 }
+
+export const maybeToPromise =
+  (catchResponse: any = 'not found') =>
+    <T>(maybe: IMaybe<T>) => maybe.isSome()
+      ? Promise.resolve(maybe.valueOrUndefined() as T)
+      : Promise.reject(catchResponse)

test/monads/maybe.spec.ts

@@ -1,4 +1,4 @@
-import { maybe } from '../../src'
+import { maybe, IMaybe, maybeToPromise } from '../../src'
 
 describe('Maybe', () => {
   describe('when returning a value with possible throw', () => {
@@ -466,4 +466,33 @@ describe('Maybe', () => {
       expect(maybe(sut3).isNone()).toEqual(false)
     })
   })
+
+  describe('maybeToPromise', () => {
+    it('should flatmap', () => {
+      const sut = new Promise<IMaybe<string>>((a, b) => a(maybe('test')))
+
+      sut
+        .then(maybeToPromise())
+        .then(result => expect(result).toEqual('test'))
+        .catch(_shouldNotBeHere => expect(false).toBe(true))
+    })
+
+    it('should catch w/ default message', () => {
+      const sut = new Promise<IMaybe<string>>((a, b) => a(maybe()))
+
+      sut
+        .then(maybeToPromise())
+        .then(_shouldNotBeHere => expect(false).toBe(true))
+        .catch(error => expect(error).toEqual('not found'))
+    })
+
+    it('should catch w/ custom message', () => {
+      const sut = new Promise<IMaybe<string>>((a, b) => a(maybe()))
+
+      sut
+        .then(maybeToPromise('err'))
+        .then(_shouldNotBeHere => expect(false).toBe(true))
+        .catch(error => expect(error).toEqual('err'))
+    })
+  })
 })