# Rust λ-calcul reference implementation

This directory contains a reference implementation of a normal order semantics λ-calculus based language.
Current syntax is based on S-expressions, ie. Lisp. There is a command-line interpreter for batch and interactive evaluation of input, and an embryonic tester daemon.

# Tester

The tester daemon is inspired by [Extreme Startup](https://github.com/rchatley/extreme_startup): It's a REST-ish server and client that allows to repeatedly send λ-terms to a remote execution engine and compare the result against its expectations.

The interaction flow is simple:

* HTTP server starts on some known port (eg. 8080)
* Client sends a `POST /register` request, passing in as payload a JSON object with a `url` and `name` string fields
  ```
  curl -v -X POST -d '{"url":"http://127.0.0.1:8888/eval", "name": "toto"}' -H 'Content-type: application/json' http://localhost:8080/register
  ```
* Obviously, client needs to start a HTTP server able to respond to a `GET` request at the given URL
* If URL is not already registered, server accepts the registration (returning a 200 result) and starts a _testing thread_
* The _tester_ then repeatedly sends `POST` requests to the client's registered URL
  * The body of the request is plain text S-expression representing a λ-term
  * The tester expects the response to be the plain text result of the evaluation of those terms
* If the client fails to answer, or answers wrongly, the server keeps sending the same request
* If the client's answer is correct, the server sends another term to evaluate and awards 1 point to the client
* The `/leaderboard` endpoint provides a crude HTML page listing each clients' current score

## Building

This software is written in Rust (sorry @xvdw), so one needs a Rust toolchain installed, then:

```
cargo build && cargo test
```

## Running

To run the server:

```
cargo run --bin server
```

There are `--port` and `--host` arguments should one want to change the default `127.0.0.1:8080`