[mpfundstein]

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(Node, v => console.log(v.value))
        .when(Tree, t => { walkT(t.left); walkT(t.right)})
        .otherwise(_ => 'error');

    const mapT = (f, t) => match(t)
        .when(Node, v => N(f(v.value)))
        .when(Tree, t => T(mapT(f, t.left), mapT(f, t.right)))
        .otherwise(_ => { throw new Error('error') });

Works also on deeply nested objects.

[1] https://github.com/MarkusPfundstein/pmatch-js

[cshepp]

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.

[mpfundstein]

If you mean by method-based pattern matching that you evaluate a function for each 'case'. My lib can do that do:

    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(' ')
    )

But maybe you mean something totally different :-)

EDIT: Ah I think I know what you mean. Your lib takes an array of tuples to define the patterns. Sorry for the confusion.

[dkarbayev]

Wow, importing the whole lodash to use just one function? There’s es6 way of getting an array with a range of numbers:

    [...Array(100).keys()].map(v=>v+1)

A little bit longer but no dependencies.

[fangaorne]

Although this method is pretty, I see 4 loops in this small line. a better way would be to only import the range method from lodash like so :

    import _range from "lodash/range";

[mpfundstein]

Pretty cool trick mate. Didn’t know