Algebraic Data Types in JavaScript | Hacker News Reader

Algebraic Data Types in JavaScript

w3future.com

45 pointsamelius5 comments

I've written something like this, essentially just providing sum types, but it'e currently embedded in some code at work. If anyone is familiar with putting ES6 NPM libraries together and would like to help, I'd be happy to open source it.

Thanks for reminding me that I really should write an updated version of that library!

  Color = Data(function() ({ Red: {}, Green: {}, Blue: {}, Yellow: {} }))

Is this JS or pseudocode? There are some extra parens in there and the pattern repeats everywhere.

That may be the "expression closure" from "javascript 1.8" that was mentioned. When was this written? 2008? I thought ES6 was the new hotness now? It just goes to show you, if you want future-proof, code in coffeescript. [EDIT:] ...which of course didn't exist until 2009. Anyway here it is:

  Color = Data -> Red: {}, Green: {}, Blue: {}, Yellow: {}

Those are the JavaScript 1.8 (FF-only) "expression closures" the author mentions. JavaScript 1.8 introduces a succinct syntax for anonymous functions:

    function (a, b, c) a + b * c;

which is the same as

    function (a, b, c) { return a + b * c; }

Of course, this syntax breaks down if you want to return an object literal from your anonymous function. Curly braces are too overloaded in JS! Adding parentheses disambiguates between the new and the old function syntax.

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