feat(maybe): extend maybe.tap, introduce tapNone / tapSome (#20)

Author: patrickmichalina

src/interfaces/maybe.interface.ts

@@ -32,7 +32,17 @@ export interface IMaybe<T> extends IMonad<T> {
   /**
    * Execute functions with side-effects.
    */
-  tap(val: IMaybePattern<T, void>): void
+  tap(val: Partial<IMaybePattern<T, void>>): void
+  
+  /**
+   * Execute a function with side-effects when maybe is a none.
+   */
+  tapNone(f: () => void): void
+  
+  /**
+   * Execute a function with side-effects when maybe is a some.
+   */
+  tapSome(f: (val: T) => void): void
 
   /**
    * Unwrap and apply MaybePattern functions

src/monads/maybe.ts

@@ -5,7 +5,9 @@ export function maybe<T>(value?: T): IMaybe<T> {
     of: (x) => maybe(x),
     valueOr: (val: T) => value === null || value === undefined ? val : value,
     valueOrCompute: (f: () => T) => value === null || value === undefined ? f() : value,
-    tap: (obj: IMaybePattern<T, void>) => value === null || value === undefined ? obj.none() : obj.some(value),
+    tap: (obj: Partial<IMaybePattern<T, void>>) => value === null || value === undefined ? obj.none && obj.none() : obj.some && obj.some(value),
+    tapNone: (f: () => void) => (value === null || value === undefined) && f(),
+    tapSome: (f: (val: T) => void) => value !== null && value !== undefined && f(value),
     match: <R>(pattern: IMaybePattern<T, R>) => value === null || value === undefined ? pattern.none() : pattern.some(value),
     map: <R>(f: (t: T) => R) => value === null || value === undefined ? maybe<R>() : maybe<R>(f(value)),
     flatMap: <R>(f: (d: T) => IMaybe<R>) => value === null || value === undefined ? maybe<R>() : f(value)

test/monads/maybe.spec.ts

@@ -270,5 +270,25 @@ describe('Maybe', () => {
       expect(maybeSomeNumber).toEqual('ok')
     })
   })
+
+  describe('when tapSome', () => {
+    it('should work', () => {
+      const sut: string | undefined = 'abc'
+
+      expect.assertions(1)
+      maybe(sut).tapSome(a => expect(a).toEqual('abc'))
+      maybe(sut).tapNone(() => expect(1).toEqual(1))
+    })
+  })
+
+  describe('when tapNone', () => {
+    it('should work', () => {
+      const sut: string | undefined = undefined
+
+      expect.assertions(1)
+      maybe(sut).tapNone(() => expect(1).toEqual(1))
+      maybe(sut).tapSome(() => expect(1).toEqual(1))
+    })
+  })
 })