refactor(maybe): reduce nested complexity (#40)

Author: patrickmichalina

src/monads/maybe.ts

@@ -1,17 +1,28 @@
 import { IMaybe, IMaybePattern } from "../interfaces"
 
-export function maybe<T>(value?: T): IMaybe<NonNullable<T>> {
+const isEmpty = <T>(value: T) => value === null || value === undefined
+const isNotEmpty = <T>(value: T) => !isEmpty(value)
+const valueOr = <T>(value?: T) => (val: NonNullable<T>) => isEmpty(value) ? val : value as NonNullable<T>
+const valueOrCompute = <T>(value?: T) => (fn: () => NonNullable<T>) => isEmpty(value) ? fn() : value as NonNullable<T>
+const tap = <T>(value?: T) => (obj: Partial<IMaybePattern<T, void>>) => isEmpty(value) ? obj.none && obj.none() : obj.some && obj.some(value as NonNullable<T>)
+const tapNone = <T>(value?: T) => (fn: () => void) => (isEmpty(value)) && fn()
+const tapSome = <T>(value?: T) => (fn: (val: NonNullable<T>) => void) => isNotEmpty(value) && fn(value as NonNullable<T>)
+const match = <T>(value?: T) => <R>(pattern: IMaybePattern<T, R>) => isEmpty(value) ? pattern.none() : pattern.some(value as NonNullable<T>)
+const map = <T>(value?: T) => <R>(fn: (t: NonNullable<T>) => R) => isEmpty(value) ? maybe<R>() : maybe<R>(fn(value as NonNullable<T>))
+const flatMap = <T>(value?: T) => <R>(fn: (d: NonNullable<T>) => IMaybe<R>) => isEmpty(value) ? maybe<R>() : fn(value as NonNullable<T>)
+
+export const maybe = <T>(value?: T): IMaybe<NonNullable<T>> => {
   return {
     of: maybe,
-    valueOr: (val: NonNullable<T>) => value === null || value === undefined ? val : value as NonNullable<T>,
-    valueOrCompute: (f: () => NonNullable<T>) => value === null || value === undefined ? f() : value as NonNullable<T>,
-    tap: (obj: Partial<IMaybePattern<T, void>>) => value === null || value === undefined ? obj.none && obj.none() : obj.some && obj.some(value as NonNullable<T>),
-    tapNone: (f: () => void) => (value === null || value === undefined) && f(),
-    tapSome: (f: (val: NonNullable<T>) => void) => value !== null && value !== undefined && f(value as NonNullable<T>),
-    match: <R>(pattern: IMaybePattern<T, R>) => value === null || value === undefined ? pattern.none() : pattern.some(value as NonNullable<T>),
-    map: <R>(f: (t: NonNullable<T>) => R) => value === null || value === undefined ? maybe<R>() : maybe<R>(f(value as NonNullable<T>)),
-    flatMap: <R>(f: (d: NonNullable<T>) => IMaybe<R>) => value === null || value === undefined ? maybe<R>() : f(value as NonNullable<T>),
-    filter: (fn: (d: NonNullable<T>) => boolean) => value === null || value === undefined
+    valueOr: valueOr(value),
+    valueOrCompute: valueOrCompute(value),
+    tap: tap(value),
+    tapNone: tapNone(value),
+    tapSome: tapSome(value),
+    match: match(value),
+    map: map(value),
+    flatMap: flatMap(value),
+    filter: (fn: (d: NonNullable<T>) => boolean) => isEmpty(value)
       ? maybe()
       : fn(value as NonNullable<T>)
         ? maybe(value as NonNullable<T>)