kylecorbelli

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))
  }
}

kylecorbelli

const safeHead = <T> (list: ReadonlyArray<T>): Maybe<T> =>
  list.length === 0
    ? Nothing()
    : Just(list[0])

kylecorbelli

import { compose, toUpper } from 'ramda'

function unsafeHead<T> (list: ReadonlyArray<T>): T {
  return list[0]
}

type UpperCaseHead = (list: ReadonlyArray<string>) => string
const upperCaseHead: UpperCaseHead = compose(
  toUpper,
  unsafeHead,

kylecorbelli

const greet = (maybeName: Maybe<string>): string => {
  switch (maybeName.type) {
    case MaybeType.Nothing:
      return 'Pleased to meet you!'
    case MaybeType.Just:
      return `Good to see you again ${maybeName.value}`
  }
}

kylecorbelli

enum MaybeType {
  Just = 'maybe-type__just',
  Nothing = 'maybe-type__nothing',
}

interface Just<T> {
  type: typeof MaybeType.Just
  value: T
}

kylecorbelli

import { curry } from 'ramda'

enum MaybeType {
  Just = 'maybe-type__just',
  Nothing = 'maybe-type__nothing',
}

interface Just<T> extends Readonly<{
  type: typeof MaybeType.Just
  value: T