maybe-module.ts

import { curry } from 'ramda'

function maybeMap<A, B> (f: (val: A) => B, m: Maybe<A>): Maybe<B> {
  switch (m.type) {
    case MaybeType.Nothing:
      return Nothing()
    case MaybeType.Just:
      return Just(f(m.value))
  }
}

function maybeAndThen<A, B> (f: (val: A) => Maybe<B>, m: Maybe<A>): Maybe<B> {
  switch (m.type) {
    case MaybeType.Nothing:
      return Nothing()
    case MaybeType.Just:
      return f(m.value)
  }
}

function maybeOf<T> (value: T): Maybe<T> {
  return value === undefined || value === null
    ? Nothing()
    : Just(value)
}

function maybeWithDefault<T> (defaultVal: T, m: Maybe<T>): T {
  switch (m.type) {
    case MaybeType.Nothing:
      return defaultVal
    case MaybeType.Just:
      return m.value
  }
}

export const Maybe = {
  andThen: curry(maybeAndThen),
  map: curry(maybeMap),
  of: maybeOf,
  withDefault: curry(maybeWithDefault),
}