Document how this would work with Arrays/Iterables/Observables

[ichpuchtli]

Could you add examples of how this syntax would look with arrays/iterables and the up coming observables spec

i.e.

var sum = [1,2,3,4,5,6,7,8,9]
   |> filter(x => x % 2 == 0)
   |> map(x => x ** 2)
   |> reduce((total, next) => total + next, 0)

[jonasem]

Keep in mind object observe will be removed from the spec.https://mail.mozilla.org/pipermail/es-discuss/2015-November/044684.html

[ichpuchtli]

Observables !== Object.Observe

[jonasem]

Good point. My bad.

[nmn]

You'd need a utility library to pull out object methods, probably.

There are a few options:

const thisify = fn => (...args) => context => fn.apply(context, args);

// Usage:
const Arr = Array.prototype;
var sum = [1,2,3,4,5,6,7,8,9]
   |> thisify(Arr.filter)(x => x % 2 == 0)
   |> thisify(Arr.map)(x => x ** 2)
   |> thisify(Arr.reduce)((total, next) => total + next, 0)

const thisify = fn => (...args) => context => fn.apply(context, args);
const extractMethods = (obj) => {
  let methods = {};
  for (let key in obj) {
    if (typeof obj[key] === 'function'){
      methods[key] = thisify(obj[key]);
    }
  }
}

// Usage:
const List = extractMethods([]); // or extractMethods(Array.prototype);

var sum = [1,2,3,4,5,6,7,8,9]
   |> List.filter(x => x % 2 == 0)
   |> List.map(x => x ** 2)
   |> List.reduce((total, next) => total + next, 0)

// Ideal Example:
Object.assign(Array, extractMethods(Array.prototype));

var sum = [1,2,3,4,5,6,7,8,9]
   |> Array.filter(x => x % 2 == 0)
   |> Array.map(x => x ** 2)
   |> Array.reduce((total, next) => total + next, 0)

I think eventually the JS built-ins should extended to include these methods statically on Array itself, without needing to use the extractMethods helper, but this is a good stop-gap.

[Qard]

Alternatively, we could just crib the &.property syntax from ruby. So you'd get something like:

var sum = [1,2,3,4,5,6,7,8,9]
   |> &.filter(x => x % 2 == 0)
   |> &.map(x => x ** 2)
   |> &.reduce((total, next) => total + next, 0)

[dallonf]

I'm not sure something like this is necessary... what's the difference between this:
(Using Qard's example, adding a flatten call to demonstrate something that will make sense in a moment)

var sum = [1,2,3,4,5,6,7,8,9]
   |> &.filter(x => x % 2 == 0)
   |> &.map(x => ([x, x ** 2]))
   |> flatten
   |> &.reduce((total, next) => total + next, 0)

and this (already supported):

var sum = [1,2,3,4,5,6,7,8,9]
   .filter(x => x % 2 == 0)
   .map(x => ([x, x ** 2]))
   |> flatten // WRONG! see below
   .reduce((total, next) => total + next, 0)

oop, actually I see it now - that above code sample doesn't do what it looks like. You would actually need something like this:

var sum = [1,2,3,4,5,6,7,8,9]
   .filter(x => x % 2 == 0)
   .map(x => ([x, x ** 2]))
   |> _ => flatten(_)
   .reduce((total, next) => total + next, 0)

Still not terrible, though.

[Volune]

@dallonf I think you mean

var sum = [1,2,3,4,5,6,7,8,9]
   .filter(x => x % 2 == 0)
   .map(x => ([x, x ** 2]))
   |> flatten
   |> _ => _
   .reduce((total, next) => total + next, 0)

Personally I would just use a custom library all the way to support iterables, generators, and not creating an array on each step.

import _ from 'some-lib';
var sum = [1,2,3,4,5,6,7,8,9]
   |> _.filter(x => x % 2 == 0)
   |> _.map(x => ([x, x ** 2]))
   |> _.flatten
   |> _.reduce((total, next) => total + next, 0)

[darthtrevino]

I haven't seen any information yet on how this proposal works with Observables. It would be rad if you could use this to compose observable streams into a processing graph.

const dataStream = readDataFromRemeteServerAsObservable()
  |> groupBy('category')
  |> max()

// vs what you do in RxJS currently:

const dataStream = readDataFromRemeteServerAsObservable()
  .pipe(
     groupBy('category'),
     max()
   )

[mAAdhaTTah]

Most relevant is #101, which talks about using Pipeline for importable methods.

[felixfbecker]

I'm baffled that RxJS operators are not mentioned in the use cases section. That seems like a way bigger use case than any of the examples mentioned

[littledan]

@felixfbecker PRs welcome to improve the examples.

[felixfbecker]

@littledan #144

[littledan]

Great text, thank you!