Pun: A small library to enable pattern matching in JavaScript and CoffeeScript | Hacker News Reader

Pun: A small library to enable pattern matching in JavaScript and CoffeeScript

github.com

73 pointsunignorant16 comments

Very cool! You might also want to check out sparkler, which uses macros to let you do this with a little better syntax: https://github.com/natefaubion/sparkler

I'd heard of sparkler, but my impression was that macros prevent it from working with CoffeeScript.

There's also matches.js, which is the deprecated precursor to sparkler: https://github.com/natefaubion/matches.js

What I'd like is a small library to complement lodash/underscore with utility functions required when using high-level ones. It's very annoying to have verbose

    _.each([1,2,3], function(x) { something(x, 'param'); }

when it could be

   _.each([1,2,3], $.call(something, _, 'param'))

It seems like the current solution is to use _.pluck() or similar functions for common use-cases, or use _.partial which I find even more verbose than standard functions.

e.g.

    _.map(objs, $.pluck('person.age'))    
    promise.then($.ret(some_fn, _, 'a'))

promise.then(some_fn) doesn't work because what we want is to return some_fn from within a function.

    promise.then(function(x) { return some_fn(x, 'a'); })

I know there are ways around, but those are not unified in a standard and coherent library that could complement other high-level libraries.

Recently watched this video, which describes why underscore is actually making this difficult through its design.

https://www.youtube.com/watch?v=m3svKOdZijA

That was a great talk! Thank you. Started out a bit hanky because of his nervousness but he pulled through and ramped up.

Happily, you're first example is actually already supported in the latest Underscore (1.6.0):

  _.each([1,2,3], _.partial(something, _, 'param'))

Example:

  _.map([1, 2, 3, 4], _.partial(Math.pow, _, 8))
  // [1, 256, 6561, 65536]

Admittedly, "_.partial" is 3 more characters than "$.call", but if you really used it a lot, you could alias it to something short like "_p".

Unfortunately, this doesn't seem to be present in the latest Lo-Dash (which I generally prefer).

Use LiveScript.

No, seriously, LiveScript is great and I used it in production already, without any problems. Your first example would look like this in LS:

    _.each [1 to 3], (something _, 'param')

where "_" in this context means partial application.

Even better, LS has special syntax for accessing an object method and binding it at the same time, this is a bit of code I wrote recently:

    httpify-promise = (promise) ->
        # add `success` and `error` methods to the promise, making it into
        # $http-compatible one
        promise with
            success: (promise~then _, null)
            error:   (promise~then null, _)

Now this is really beautiful and powerful.

I also played with promises some time ago, in Node, where I used q library and LiveScript. Partial application and curried functions from prelude-ls let me write code like this:

    read-dir(directory)
        .then map (path.join directory, _)
        .then get-stats
        .then tee (collect-files-into accum)
        .then filter (at 1)
        .then walk-subdirs
        .thenResolve accum

(the whole file here: http://klibert.pl/walkfiles.html)

In short, having support for many higher-level idioms as part of a language, as opposed to library, makes it MUCH more pleasant to work with.

That tee + thenResolve pattern is a first for me. Is this from LS or did they take it from another lang/lib ?

It's actually a very little function I wrote, based on `tee` Unix shell command: http://unixhelp.ed.ac.uk/CGI/man-cgi?tee

It looks like this:

    tee = (func, val) --> func(val); val

which could be equivalently written as:

    tee = (func) -> (val) -> func(val); val

In other words it's an identity function which additionally executes some other function for side-effects. In the shell the `tee` command always writes to the file, while my version can execute any side-effect, but I think my version is just a generalization of the standard Unix command and so I named it like this.

I'm sure this function has its own, formal name, with the word "monad" or "combinator" (maybe K combinator?) in it, but I wasn't patient enough to research it :)

`thenResolve` is a standard method on a promise object implemented by the Q library (https://github.com/kriskowal/q/wiki/API-Reference#promisethe...) I used, it's equivalent to

   .then () -> accum

In other words, `thenResolve` appends a success callback which discards previous value and always returns another value.

Once again, take a look at the full source at http://klibert.pl/walkfiles.html - I'm going to update it with a full explanation of what's going on, but even right now it's only 90 lines with including comments, and should be a good example of main LS strengths. I'm probably going to write another example which makes use of even more (and more advanced) LS features when I'm done with explaining this one.

Actually my reflection started with using tee and pipes in bash, having a desire to sync/join on the multiple paths created by tees. Interesting job that you did.

A quick comparison of some Python implementations I found via quick Googling:

https://gist.github.com/andybak/45e3155420d18420a34a

Nice, that's a clever use of decorators. A bit annoying that you need repeated "defs", though.

Here's another approach based on Macropy (basically, macros for Python): https://github.com/lihaoyi/macropy#pattern-matching.

Very awesome.

Also see LiveScript http://livescript.net/

This is cool but I would love if these features were implemented at compile time instead of using functions. Great work either way!

I love this kind of stuff.

Every time I see things like this I'm grateful for Dart SDK

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