Functional stuff (pipeline, autocurry)

functional-stuff.js

// test-driven with Ji (benchristel.github.com/ji)

// tests go here
// hint: open the javascript console for better failure messages

expect(start(1).done, eq, 1)
expect(start(2).done, eq, 2)

expect(
  start(2)
  	(multiply(3))
  .done
, eq, 6)

expect(concatArgs([1, 2], [3, 4])[2], eq, 3)

expect(
  start(2)
  	(multiply(3))
   	(add(5))
  .done
, eq, 11)

expect(add3(1, 2, 3), eq, 6)
expect(add3(1, 2)(3), eq, 6)
expect(add3(1)(2)(3), eq, 6)
expect(add3(1)(2, 3), eq, 6)
expect(add3(1)(2, 3, 4), eq, 6)

// production code goes here

function start(input) {
  var pipe = function(fn) {
    return start(fn(input))
  }
  
  pipe.done = input
  
  return pipe
}

let multiply = autocurry(2, (a, b) => a * b)

let add3 = autocurry(3, (a, b, c) => a + b + c)

let add = autocurry(2, (a, b) => a + b)

function autocurry(nArgs, f) {
  return function() {
    var firstArgs = arguments
    if (firstArgs.length < nArgs) {
      return autocurry(nArgs - firstArgs.length, function() {
        var restArgs = arguments
        return f.apply(null, concatArgs(firstArgs, restArgs))
      })
    } else {
      return f.apply(null, firstArgs)
    }
  }
}

function concatArgs(a, b) {
  var output = []
  for (let item of a) {
    output.push(item)
  }
  for (let item of b) {
    output.push(item)
  }
  return output
}