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

kylecorbelli

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

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

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

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

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

type UpperCaseHead = (list: ReadonlyArray<string>) => Maybe<string>
const upperCaseHead: UpperCaseHead = compose(
  Maybe.map(toUpper),
  safeHead,
) as UpperCaseHead

console.log(upperCaseHead([])) // { type: Maybe.Nothing } ie. Nothing
console.log(upperCaseHead([ 'rick', 'morty' ])) // { type: Maybe.Just, value: 'RICK' } ie. Just 'RICK'

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

module Html where

import           Control.Monad.Reader (Reader, ask, runReader)
import           Data.List   (intercalate)
import           Prelude     hiding (div)

type Html = String
type Email = String

div :: [Html] -> Html

kylecorbelli

main :: IO ()
main =
  putStrLn "what is your email address?" >>
    getLine >>= \email ->
      putStrLn . show $ view email

view :: Email -> Html
view email =
  div
    [ page email