alpaca_elli_example

A very simple Alpaca example application providing two HTTP endpoints with elli.

In preparing for the Alpaca v0.2.8 release this has turned up a number of basic usability issues for Alpaca:

• no source annotations in the code generator output makes for a quite frustrating development and debugging experience as this means no stack traces! This will be pretty much top of my list for v0.2.9 and I might even delay v0.2.8 for it.
• exhaustiveness checks when using pattern matching in function heads can fail when the checker tries to load a type from a module that has already been compiled. E.g. if elli_request.alp has already been built successfully, exhaustiveness checks of endpoint.alp will throw errors because the module for elli_request.alp doesn't appear to be available.
• incorrect line numbers in some type errors.
• some frustrating issues around multi-arity functions and type specifications for them e.g. there appear to be problems when handle/1 and handle/2 both exist but only a spec for handle/1 is available. I haven't dug into this too deeply yet so it may be more complicated or even rather simple.

This currently uses some pending changes to the rebar3 plugin from lepoetemaudit that allow a pre-built version of Alpaca to be used directly.

Build and Run

You will need a local build of Alpaca, basic steps:

• clone the language repository
• build a local untagged Alpaca distribution
• set the ALPACA_ROOT environment variable to the location of your local Alpaca build

Here are the basic steps:

$ git clone https://github.com/alpaca-lang/alpaca.git
$ cd alpaca
$ rebar3 compile
$ bash ./make-release.sh
$ export ALPACA_ROOT=`pwd`/alpaca-unversioned_

Then you should be able to build and run this elli example:

$ cd $WHEREVER_YOU_CLONED_THIS_REPO
$ rebar3 clean
$ rebar3 release
$ ./_build/default/rel/alpaca_elli_example/bin/alpaca_elli_example foreground

Then:

➜  alpaca_elli_example git:(master) ✗ curl localhost:3000/test
Test endpoint.
➜  alpaca_elli_example git:(master) ✗ curl localhost:3000/hello/world
Hello, world
➜  alpaca_elli_example git:(master) ✗ curl localhost:3000/hello/Wat
Hello, Wat
➜  alpaca_elli_example git:(master) ✗ curl -X PUT localhost:3000/hello/Wat
Not found
➜  alpaca_elli_example git:(master) ✗