Fun for Selwyn

bigTest.txt

Hello.  how are you?
Hello.  how are you?
Hello.  how are you?
Hello.  how are you?
Hello.  how are you?

index.js

const {
  Async, constant, curry,
  mapReduce, maybeToAsync,
  safe
} = require('crocks')

// FileAsync :: Async Error String

// access :: (String, Number) -> Async Error ()
const access =
  Async.fromNode(fs.access)

// read :: (String, String) -> Async Error a
const read =
  Async.fromNode(fs.readFile)

// load :: String -> FileAsync
const load = file =>
  access(file, fs.constants.R_OK)
    .chain(constant(read(file, 'utf-8')))

// files :: [ String ]
const files = [
  './missing.txt',
  './test.txt',
  './bigTest.txt'
]

// first :: (a -> Boolean) -> FileAsync -> FileAsync -> FileAsync
const first = curry(
  (pred, acc, x) =>
    acc.alt(
      x.chain(
        maybeToAsync(new Error('thou shall not pass'), safe(pred))
      )
    )
)

// readFirst :: (String -> Boolean) -> [ String ] -> FileAsync
const readFirst = curry(
  pred => mapReduce(
    load,
    first(pred),
    Async.Rejected('nothing to read')
  )
)

// isValid :: String -> Boolean
const isValid =
  x => x.length > 25

readFirst(isValid, files)
  .fork(
    console.log.bind(console, 'rej\n'),
    console.log.bind(console, 'res\n')
  )

test.txt

Hello.  how are you?