composable-callbacks.js

const after = t => x => cont => {
  const id = setTimeout (cont, t, x)
  return () => clearTimeout (id)
}

const map = f => run => cont => run(x => cont (f (x)))
const chain = f => run => cont => run(x => f (x) (cont))

const run = chain (x => after (2000) (`${x}C`))
                  (map (x => `${x}B`)
                       (after (1000) ('A')))


const cancel = run (console.log)

// calling cancel will clear the timeout and allow the process to exit
// cancel()

with-rejection-branch.js

const fs = require('fs')

const pipe = fs => fs.reduce ((f, g) => x => g (f (x)), x => x)

const readFile = p => rej => res => {
  fs.readFile (p, 'utf8', (e, x) => e ? rej (e) : res (x))
  return () => {}
}

const after = t => x => _ => res => {
  const id = setTimeout (res, t, x)
  return () => clearTimeout (id)
}

const map = f => fork => rej => res => fork (rej) (x => res (f (x)))
const chain = f => fork => rej => res => fork (rej) (x => f (x) (rej) (res))

const program = pipe ([ readFile
                      , map (x => x.trim ())
                      , map (x => `${x}B`)
                      , chain (x => after (2000) (`${x}C`)) ])

const fork = program ('test.txt')

const cancel = fork (e => console.error (`Handled ${e}`))
                    (console.log)