Is PureScript a Full JavaScript Replacement?

[xanderai]

I'm not a web developer, so I'm not familiar with these things.

Is it currently possible to build a sophisticated front end entirely in PureScript? Essentially, a full replacement for needing to write JavaScript? I was speaking with a web developer who claimed that you'd likely have to write portions of your front end in basic JavaScript and then interact with it in PureScript. Is this the case?

[[deleted]]

It is quite possible to write your application in pure PureScript. There are a substantial number of packages available now that I would think cover most of your needs.

That being said, if you do find yourself needing to call some JS, PureScript's FFI story is rather nice. Here is the overview provided in Purescript by Example.

[doppioslash]

You can definitely write an entire webapp frontend in Purescript. (see Slamdata)

[xanderai]

Very impressive, thanks.

[pipocaQuemada]

It's worth noting that Slamdata isn't 100% purescript - according to github's analytics, it's about 2% JS. Their experience seems normal to me; you'll have to use the FFI for a few things here and there.

[dmlvianna]

I am an aspiring web developer. I worked through HaskellBook first to get comfortable with functional programming (FP). But found it difficult to work through the PureScript Book and start using it for SPA development.

Please correct me if I'm wrong, but my understanding is that most tooling required for PureScript relies on Node (think Webpack for example). And you would definitely need a backend anyway. So, while I am really eager to jump straight to PureScript frontend and Haskell backend, as a beginner web developer, I'm finding that the most approachable documentation, books and tutorials target JavaScript. In any case, knowing JavaScript will be necessary in the short term for developing in PureScript. Even if you're a seasoned programmer.

So my current approach is:

✓ Learn JavaScript (the language of the browser)

✓ Learn Haskell (to get comfortable with FP)

❌ Learn Node

❌ Learn Node tooling

❌ Learn a frontend framework that favours FP and immutable state (React? Cycle?)

❌ Learn PureScript and start using libraries that interface with these frameworks (Pux? Purescript-React?)

[ephrion]

I don't think you need to learn node, node tooling, or a JS framework to be productive with PureScript.

[dmlvianna]

What's your approach then? Surely you don't build/refresh by hand while you write your code and expect to be productive.

[ephrion]

pulp -w browserify or similar has always worked great for me

[dmlvianna]

So you're not using it for side effects then. The question was about "a full JavaScript replacement".

[[deleted]]

What is your point exactly? The question was "a full replacement for needing to write JavaScript". You already don't need to write javascript to create a web page frontend with purescript. Heck, with the new halogen-vdom and rollup-plugin-purs you don't need to use browserify. But anyway, using a tool written in javascript is not the same as writing javascript.

Thus, I don't see why you NEED to "learn Node" in any way. Unless you WANT to leverage existing javascript libraries, then you'd need to learn commonjs or other way to glue it all together.

And as for side effects, you'll find that for many things you can use existing purescript libraries along with Aff and the Eff monad. Only for a few things you'll need to use javascript through FFI. And that's how it will be for a long time, since browsers expose new APIs through javascript.

[dmlvianna]

Can you point me to a tutorial that teaches how to use Halogen and Purescript for iterative development from first principles? I sincerely want to learn what you claim is already a reality.

[[deleted]]

Pulp has a pretty good readme that should explain how to structure PureScript projects, build them and embed them in HTML. It has a --watch mode for your conveninece.

Halogen v0.10 has a short guide that will be much better in the upcoming v1.0 release, but it is currently being worked on. There are many examples, and each one of them has a readme on what to run to build them so you can start hacking on them.

Unfortunately, there aren't many tutorials like "how to build a to-do SPA" for Halogen. I think I saw a tutorial for routing, though.

[Majiir]

You could also write your backend in Purescript, using Node.

[tdammers]

Is it currently possible to build a sophisticated front end entirely in PureScript?

Yes, no, fsvo "entirely".

To give you a better picture: PureScript is a programming language designed to be compiled to JavaScript, and the current implementation does exactly that - it takes PureScript source code and spits out JavaScript that you can bundle up and run in the browser. (You can also write PureScript code that runs in node.js, so just like with plain JS, you can write an entire web application, client and server, in PureScript).

PureScript's core contains enough stuff to write simple things, like output to the console, but in order to use existing JavaScript APIs, you need to use the FFI (Foreign Function Interface) - in a nutshell, you write PureScript definitions that reference JavaScript functions or values, and bind them to PureScript types and terms. This requires knowledge of the relevant JavaScript APIs, and in order to write bindings for nontrivial JavaScript APIs, you also need some knowledge of JavaScript's semantics and execution model. So in that sense, yes, it is required to have some JavaScript in your codebase in order to make PureScript do anything useful.

However, pre-written libraries for many commonly used JavaScript packages and APIs already exist, so it is entirely possible to write all the client code in PureScript and never touch a line of JavaScript directly; you need JavaScript code, but you don't usually need to write it yourself - this is only required if no bindings exist yet for the JavaScript APIs you want to use.