Compose with Promises, using pointfree programming #javascript #functional #programming #pointfree

index.js

let composeP = (...fns) => p =>
  fns
    .reduceRight(
      (acc, it) =>
        Array.isArray(it)
          ? acc.then(it[0], it[1]) // ).catch(
          : acc.then(it), 
      p
    );

const throwErr = () => { throw Error('RGT Ahhh Err'); }

// utils
const log =
  tag => val =>
    (console.log(tag, val), val);

const inc =
  a => b => a + b;

const constant = x => () => x;

let reject = msg => Promise.reject(Error(msg))


// implementation
const process = composeP(
  constant(99),
  [log('succ'), log('eh, sorry')],
  // reject,
  throwErr,
  constant('err klk'),
  log('step 2'),
  inc(2),
  log('step 1'),
  inc(1)
);


process(Promise.resolve(1))
  .then(log('final')).catch(() => console.log('Por si aca'))
  .then(() => console.log('Ahora si'));