Sunday, May 18, 2014

lfest: A Routing Party for LFE Web Apps

The Clojure community (in particular, James Reeves) has produced one of the best APIs I've seen for creating RESTful services, or any application using path dispatching (routing), really: Compojure.

I've been really missing this in LFE. Despite the fact that creating RESTful apps in LFE with YAWS is so simple it doesn't even need a framework, the routes can be a bit difficult to read, due to some of the destructuring that's done (e.g., URL paths).

Take the following route declaration from the yaws-rest-starter project:

Note that this example delegates additional routing to other functions, since all the routing in one function was pretty difficult to read. This, however, detracts from the overall readability in a different way: there's not one place to look to see what functions map to the complete URL-space for this service.

I wanted to be able to do something like what you can do in Clojure:

LFE is a Lisp with macros, so why not? Also, nox or mheise (I forget who) on the #erlang-lisp channel had previously noted all the lfe* projects (and these too), and suggested that someone create the inevitable "lfest" repo on Github.

Enter lfest. After a weekend of hacking and debugging some tiny macros, surprisingly little code now supports routes definitions like the following in LFE+YAWS web apps:

If you're curious to see what this actually expands to before getting compiled in a .beam file, you can view it here.

Bonus for LFE webdevs: this project also has a module of HTTP status codes, for easy re-use in other projects.

The recent work I've been doing with macros has really helped shape the section I've been planning to write in the LFE User Guide. I haven't wanted it to be yet another dry description of macros in a Lisp-2. Instead, my hope is to help jump-start people into how to think about macros, how to start writing them immediately (without years of study first), and how to debug them.

The trick, as with all complicated subjects, is how to remove the barrier to entry and get folks that necessary hands-on experience without dumbing-down the material. It's almost ready...

Also, it's Bay to Breakers today, and Ocean Beach is bumpin. The synchronicity is just eery. May you party just as hard with routes in LFE.

Wednesday, May 07, 2014

LFE Design Summit

Well, maybe not summit, but certainly a meeting of minds :-)

The LFE Community is pleased to announce that we will be holding our first ever community design meeting in Stockholm, Sweden this June during the Erlang User Conference! We have set aside 1 hour for a kick-off discussion that we can continue in breakout sessions, hallways, meadhalls, in #erlang-lisp on Freenode, and on the LFE mail list

Our goals are to not only share plans, but to discover what you want in LFE, how you want to use it. This is an opportunity for us to work together, explore interesting problems to solve, build community awareness around language goals, and identify efforts around which each of us are interested in collaborating with others in the course of subsequent months.

We've opened up a Google Docs form so you can add your ideas for session topics. Here are some discussion topics that we've come up with so far:
  • LFE Standard Library 
  • Java Interop via Erjang 
  • State of LFE/LFE Roadmap 
  • Specs, Types, Debug Info and Dialyzer: Erlang Core AST in BEAM 
  • Refining LFE docs and guides, creating a CookBook, etc.
Add your favorites!

In the next couple weeks, we'll identify the top session topics the folks have proposed and attempt to cover these during the Erlang User Conference. Robert was able to get us some meeting space & time for this; he's hoping to have something viewable on the EUC site soon.

This is a first step; let's see how this goes, and if people really enjoy it, we can have a real summit next time!

Update: Robert has announced the time and place.