PureScript: a statically typed language which compiles to JavaScript

https://github.com/purescript/purescript

by bpierre • 12 years ago

175 78 12 years ago

derengel• 12 years ago

From the project docs: "Generate simple readable Javascript" - isn't this more of a disadvantage than an advantage? the created Javascript code won't be high performance, which matters a lot in mobile today.

paf3113• 12 years ago

"Simple readable JavaScript" as opposed to the sort of output you might expect from compilers for other Haskell-like languages which attempt to preserve Haskell's semantics. Certainly there are cases where using techniques from pure functional programming can lead to poor performance (monadic recursion jumps to mind), but it is perfectly possible to write fast code using PureScript. And if you really need to squeeze out every last bit of performance, you can always write code in JavaScript and use the FFI.

geoffc• 12 years ago

I can vouch for the real world performance. Phil has used Purescript to dramatically improve the performance of our medical image viewer. It's pretty impressive stuff.

eru2• 12 years ago

What's monadic recursion?

BinaryIdiot3• 12 years ago

Your minification process should be separate from your build process that's required to run it. This can generate JavaScript that's not a huge pain in the ass to debug, then you as the developer can minify it with existing libraries.

Though I'm not necessarily sure it wouldn't be high performance just maybe a hair slower to load. Then again I don't know how well their generator works.

paf3113• 12 years ago

PureScript developer here. Happy to see this here, and happy to answer any questions.

mhd• 12 years ago

With some languages, a big part of the selling point is that it's the same or similar to a language the programmer already uses. Clojure and ClojureScript come to mind, or even server-side JavaScript. Now, with ClojureScript, another common selling point is the synergy with react -- something that would appeal even to people not using Clojure (maybe because they're averse to the JVM).

So where is PureScript positioned related to this? Let's say I'm writing a backend in Ruby or Python and not Haskell, why PureScript instead of CoffeScript or sweet.js?

(I'm actually interested in this, not intended as a put-down.)

paf3113• 12 years ago

I think it's definitely possible to put knowledge of Haskell to use in PureScript, but it's not like Fay, Haste, GHCJS etc. where you can copy code verbatim. I think of PureScript as "an environment in which to write principled JavaScript". That requires that, to a certain extent, you should have JavaScript's semantics in the back of your mind while developing. For that price, you get ease of debugging and some tools which you don't have in many other compile-to-JS languages (an expressive type system, type classes, ability to refactor with confidence etc.)

Of course, one of the best things about AltJS is the interoperability with other languages. PureScript won't be the best tool for every case, but it has a simple FFI. It's possible to write complete front-ends in PureScript, but I'd love to see more examples where PureScript is used alongside something else (I've used TypeScript with PureScript successfully, for example).

mariusmg• 12 years ago

Care for a little comparation with TypeScript ? If i know TS why should i look at PS ?

paf3113• 12 years ago

(Copied from below) I've written quite a lot of TypeScript, and I generally feel very productive in it, but occasionally I feel like I want more from the type system (type classes, rank-N types, sum types, etc.) and tidier syntax. You might be interested in Bodil Stokke's recent Strange Loop talk, where she discusses why she switched from TypeScript. https://www.youtube.com/watch?v=yIlDBPiMb0o

alkonaut4• 12 years ago

Is there any particular reason why PureScript was designed with a single number type (so no proper ints)? I know that's how JS sees things, but now with a whole proper type system it would seem like we should have proper numbers? I admit I haven't read the entire docs, is there a way to e.g. have the type checker ensure a number field such as a year in a date isn't assigned a non integer?

JoshTriplett2• 12 years ago

Consider what it would take, writing in C, to store and compute integers in the "double" type, including range checks after every operation. Unless you go the asm.js route or otherwise ensure that your JIT special-cases integers, constructing range-limited integer types out of JavaScript doubles has a non-trivial cost.

Personally, it surprises me that with all the years of extensions to ECMAScript, nobody has added 1) sized integer types like word32, word64, and so on, and 2) transparent bignums, similar to int/long in Python.

paf3113• 12 years ago

It has been discussed before: https://github.com/purescript/purescript/issues/396

The reason I have been against the idea so far is that an integer type is easily accomplished using the FFI and user code. Here is one example (not quite what you're asking for, but hopefully instructive): https://github.com/darinmorrison/purescript-int64

jp_rider2• 12 years ago

This looks really cool! Do you currently have any abstractions for interacting with DOM elements?

alex_berg• 12 years ago

I'm only a bystander, but I believe PureScript doesn't include data-to-DOM binding. If you want to do it manually, I would look at the Eff monad[1].

It sounds like there are adapters to few popular frameworks, like React [2] and Angular [3].

[1] https://leanpub.com/purescript/read#leanpub-auto-the-eff-mon... [2] https://github.com/purescript-contrib/purescript-react [3] https://github.com/purescript-contrib/purescript-angular

I'm guessing a JS-controlled framework, like React or Mithril, would be a better fit if you choose to use PureScript as a core piece of your app, as they are function-based, like PureScript.

paf3113• 12 years ago

There are a few options, but the most fully-formed is probably purescript-react. I'm also interested to see where the virtual-dom bindings go. The last chapter of the book covers how you might go about writing a library for working with DOM elements in PureScript.

toadkicker3• 12 years ago

Why do I need statically typed languages to compile to Javascript? Isn't it just better to learn functional programming and dynamically typed languages?

chriswarbo• 12 years ago

If you don't write Web stuff, you can ignore JS completely, and PureScript too.

If you prefer dynamically-typed languages, use them directly (JS, CoffeeScript, etc.)

If you prefer statically-typed languages, you must care about a dynamically-typed language, since every statically-typed language can be thought of as a dynamically-typed language + a machine-checkable safety net. For example, Haskell/ML/etc. are built on Lambda Calculus, C/FORTRAN/etc. are built on machine code. If you're programming for the Web, why not use JS as the dynamic part of your language (the "computational content")?

rtfeldman• 12 years ago

It's been picking up a lot of steam lately! Bodil gave a great talk on it at Strange Loop last week: http://www.youtube.com/watch?v=yIlDBPiMb0o

tisue• 12 years ago

Saw two great talks about PureScript at Strange Loop last week, one by the language designer, Phil Freeman, and another by Bodil Stokke. Both the language and — almost equally importantly! — the accompanying book seem really well done to me.

agumonkey• 12 years ago

Indeed, the book covers a large set of very interesting topics without ceremony.

romaimperator• 12 years ago

Here's a gem to use PureScript files with Rails and the asset pipeline. It let's you add and compile PureScript files similar to how CoffeeScript files are added. https://github.com/romaimperator/purescript-rails

boothead• 12 years ago

Just bought the book today ($10 is too low!). After a few nixos hiccups today, so far so good :-)

giulianob• 12 years ago

What's the advantage over something like TypeScript which is a superset of JavaScript but supports types as well?

mck-• 12 years ago

Or Dart for that matter?

paf3113• 12 years ago

I've written quite a lot of TypeScript, and I generally feel very productive in it, but occasionally I feel like I want more from the type system (type classes, rank-N types, sum types, etc.) and tidier syntax. You might be interested in Bodil Stokke's recent Strange Loop talk, where she discusses why she switched from TypeScript. https://www.youtube.com/watch?v=yIlDBPiMb0o

moomin• 12 years ago

If you want types like Java, TypeScript's probably a good choice. However, if you want the flexibility or the guarantees a powerful type system gives you, TypeScript's not going to cut it.

chowells• 12 years ago

The advantage is that types aren't optional. People actually have to respect them.

hawleyal• 12 years ago

noelwelsh2• 12 years ago

Typescript vs Elm? Fight!

(I.e. what are the relative strengths and weaknesses of these two "modern languages targeting JS" offerings?)

gregwebs• 12 years ago

I think you meant Purescript vs Elm. disclaimer: I have used neither.

Elm has its own package manager, not sure if that is good or bad!

The biggest difference is that Elm is almost incidentally a similar strongly typed functional programming language and its biggest focus has always been on FRP (functional reactive programming) to simplify UI programming in the browser.

noelwelsh2• 12 years ago

Yes, I meant Purescript.

sassyalex• 12 years ago

Great language, but javascript code is clean, why not only keeping javascript style and adding typechecking and es6 by default..

andrewchambers• 12 years ago

Javascript being clean is your own (possibly misinformed) opinion.

pmontra• 12 years ago

I agree that's a matter of opinions but I think that the OP has a point. JavaScript is easy to understand for everybody coming from C, Java or PHP even if its core is very different from those two languages. Haskell might be cleaner but it's difficult to get for people that used only procedural languages, which are most of the programmers working today (especially if the expected domain for PureScript is web programming, frontend or backend).

There is a functional language called Elixir which runs on the Erlang virtual machine. Elixir has been designed to look like Ruby even if it's very different. That makes Ruby programmers (and maybe Python ones too) feel at ease in their first approaches with the language. When you realize how different the two languages really are you already grokked enough of Elixir to keep you going. There isn't that feeling of "oh my, I can't make it" one might have when looking at code like this http://svn.openfoundry.org/pugs/src/Pugs/Eval.hs when knowing only about C/Java/PHP/Python/Ruby

Anybody knowing Ruby or possibly Python should compare that with this https://github.com/elixir-lang/plug/blob/master/lib/plug/con...

So, my take is that if a language designer wants to create a functional language that will lure really many procedural programmers into it, s/he has to design something that looks like C or Java. PureScript is too much like Haskell (plus I hate indentation-sensitiveness, but that's almost only a subjective matter). Time will tell.

BinaryIdiot3• 12 years ago

JavaScript has some things in it that shouldn't be used but that's true with almost any language out there. There is no reason you can't write clean, easy to read and understand, code in JavaScript. I'm not sure why you're saying he may be misinformed; you can write really great code in JavaScript.

NaNaN• 12 years ago

Markdown code and JavaScript code are both clean. Now people know how to "kill" JavaScript, but it may become the new assembly language.

cmdrfred2• 12 years ago

I'm new to this but can someone enlighten me about what is the advantage of using this over pure JS?

gamegoblin• 12 years ago

Type correctness can help eliminate an entire class of bugs (type mismatch bugs) found in dynamically typed languages, or various gotchas with implicit typecasting.

cmdrfred2• 12 years ago

Thank you. I know Python, JS, and PHP so type correctness is kinda foreign to me.

toadkicker3• 12 years ago

This is where I find programmers who are comfortable with static languages struggle with dynamic languages. There is a lack of understanding and this is yet another language trying to fix something that isn't fundamentally broken.

zak_mc_kracken• 12 years ago

For those of you who want to see some code:

https://leanpub.com/purescript/read

lemming2• 12 years ago

One thing I couldn't see anywhere - is PureScript strict rather than lazy?

paf3113• 12 years ago

It uses JavaScript's evaluation model - i.e. strict, but you can write lazy code using libraries, such as purescript-lazy.

lemming2• 12 years ago

Interesting, thanks - I've been interested in a language like the Haskell.Next that SPJ described: strict evaluation but with effects controlled by monads. I'll give it a look!

billpg• 12 years ago

I find JS a thoroughly unpleasant language to work with. When will we reach the point where JS could be abstracted away entirely? (Just like how I never need to interact with assembly language any more.)

rattray2• 12 years ago

In what ways does CoffeeScript not suit you perfectly?

marrs• 12 years ago

Not speaking for the parent, CoffeeScript is even worse than Javascript. The killer for me is indentation forming scope. If you accidentally indent your code incorrectly, like when you're copy/pasting from one file to another, you can change the scope of all of the variables within.

The other major problem I have with it is that it encourages us to go back to the class-based patterns that we've been trying to get away from.

dandare• 12 years ago

typescript

afsina• 12 years ago

Dart

bru• 12 years ago

There are several paths:

1. JS as an assembly language. This is what emscripten[0], a LLVM bytecode-to-JS does, by following the asm.js specification[1]. This is for CPU-intensive tasks, not DOM manipulation. You can use any language that has a LLVM frontend.

2. JS as a target language, from a specific, new language. Those include cleaner variants that keep the same semantics (CoffeeScript, TypeScript, maybe Dart, ...) or more innovative ones, such as Elm[2], which is written in Haskell too. I'd say that a big innovation that makes the life easier is FRP (which is at the heart of Elm or React.js).

I fail yet to see what advantages PureScript brings compared to Elm.

0: https://github.com/kripken/emscripten 1: http://asmjs.org 2: http://elm-lang.org/

paf3113• 12 years ago

I fail yet to see what advantages PureScript brings compared to Elm.

I think they fit different use cases. Elm is excellent at interactive web apps using FRP. PureScript is a little more general purpose and has a few type system features which Elm currently does not (type classes and rank N polymorphism). Also, PureScript's generated code is a bit simpler and doesn't need a runtime library.

pjmlp2• 12 years ago

Looks nice, but my employer will never use anything other than JavaScript as browser language, unless a customer asks to do so.

lmm• 12 years ago

Get a better employer. I can understand thinking that e.g. existing options are not mature enough, but "never" is a stupid policy.

pjmlp2• 12 years ago

Quoting myself

unless a customer asks to do so.

which I agree with.

Since 1986 I already have seen too much technology come and go, to be convinced to use "language of the month" at work.

BinaryIdiot3• 12 years ago

Seeing these types of experiments are always interesting but just like CoffeeScript it requires learning two languages instead of one [so you an debug] which makes it a hard sale. Why not just write clean JavaScript? I know many want to make JavaScript the assembly language of the web but JavaScript is so much more complex than assembly I'm not sure that's necessarily a good goal to have.

Granted I would love for more languages to be usable on the web; even if I thought JavaScript was the best language it's always good to have competition and alternatives. But I think that has to come through browser support. I wonder how feasible it would be to generate some sort of byte code similar to how Java and others work with the JVM.

Tloewald• 12 years ago

I wish a fraction of the effort going into "fixing" javascript went into fixing the real abomination: the DOM API (and CSS). Then everyone would benefit, even people using Dart, Coffeescript, and TypeScript.

chadillac• 12 years ago

I wish people would just realize that JavaScript isn't going anywhere and make the effort to understand it instead of trying to gloss over the quirks of it.

Understanding the key parts of writing JS (closures, scope, GC, etc.) isn't all that hard and it seems like more efforts are geared towards an abstraction layer and/or framework than just learning the language in the first place.

I think it's syntax and familiar looking and feeling environment cheerfully misleads people into thinking they are in a comfort zone, while they thrash around throwing sand in their own eyes, albeit with a familiar looking bucket and shovel.

PureScript: a statically typed language which compiles to JavaScript

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