JavaScript Pattern Matching Proposal

Post by bterlson » Wed, Apr 25, 2018, 9:03 PM UTC

abritinthebay wrote: post #171

bterlson wrote: post #136

I think it's good to note that this proposal is not far along the process. Pattern matching, if it clears TC39 (a tall order, to be honest), won't land in a spec for half a decade at least I would bet. So, keep the feedback coming, and don't worry that you'll have to learn this syntax tomorrow. It's still very early, and I wouldn't be surprised if there are at least a couple major revisions before anything like this…

> if it clears TC39 (a tall order, to be honest), won't land in a spec for half a decade at least I would bet. Given current speed of iteration I think you can cut that in half. The key will be implementations - Babel plugins help with that.

Post by Zacru » Wed, Apr 25, 2018, 9:05 PM UTC

codedokode wrote: post #53

Zyst wrote: post #43

Earlier quoted context omitted.

In fairness I think that would look a bit more like this: const getDate = (date) => { switch (date) { case 1: return 'mon' case 2: return 'tues' default: return 'wed' } } let date = getDate(1) Which is, of course, still less terse. What I normally use when I have cases like this is an object-as-a-map. IE: const dates = { 1: 'mon', 2: 'tues' } let day = dates[3] || 'wed';

By the way, I don't think it is a good idea to write a function as a constant. Please compare this function getDate(date) { .. } to this: const getDate = (date) => { ... } The first version is more readable. We instantly see that it is a function and in a second case it looks like a constant at first. Also without the equal and arrow sign it looks simpler.

Post by mpfundstein » Wed, Apr 25, 2018, 9:14 PM UTC

cshepp wrote: post #169

mpfundstein wrote: post #135

Earlier quoted context omitted.

Shameless plug but here is my pattern machter [1] :D Example: // simple factorial const factorial = n => match(n) .when(0, 1) .otherwise(n => n * factorial(n - 1)); // walking a tree class Tree { constructor(left, right) { this.left = left; this.right = right; } } class Node { constructor(value) { this.value = value; } } const T = (l, r) => new Tree(l, r); const N = v => new Node(v); const walkT = t => match(t) .when…

Method-based syntax for pattern matching is easier to read and grok (IMO), but it lacks the dynamic capabilities of data-oriented syntax (in Kasai, patterns can be built/manipulated at runtime). It's interesting to compare the two approaches.

    const match = require('pmatch-js')
    const _ = require('lodash')

    const fizzbuzz = x => match(x)
      .when(a => a % 3 == 0 && a % 5 == 0, 'fizzbuzz')
      .when(a => a % 5 == 0, 'buzz')
      .when(a => a % 3 == 0, 'fizz')
      .otherwise(a => a)

    console.log(
      _.range(1, 101).map(fizzbuzz).join(' ')
    )

Post by faitswulff » Wed, Apr 25, 2018, 9:21 PM UTC

m0meni wrote: post #6

Pattern matching seems to be very trendy/popular right now. It's a big jump from JS, but https://reasonml.github.io has very nice pattern matching that you can use, and it integrates with the JS ecosystem very nicely.

Post by aylmao » Wed, Apr 25, 2018, 9:27 PM UTC

westoncb wrote: post #164

sibeliuss wrote: post #154

Earlier quoted context omitted.

With JavaScript being the most used language in the world I highly doubt the old stereotypes still apply

Is it the most used language in the world? Seems like I keep hearing comments like that, but the rankings I've seen don't list it that way.