# 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 overall interaction flow is the following:

* HTTP server starts on some known port (eg. 8080)
* Clients register themselves with the server
* Server registers client and starts sending expressions to evaluate
* Leaderboard is updated depending on whether clients' answers are correct or not

## Detailed Interactions

We use the following variables to represent, well, variable elements that should be replaced depending on the actual deployment:

* `SERVER_BASE_URL`: the base URL of the server, should be communicated by facilitator in some ways, eg. `http://1.2.3.4:8080`,
* `CLIENT_URL`: URL of a client as defined by their specific implementation.

### Registration

The client needs to send a `POST /register` request, passing in as payload a JSON object with a `url` and `name` string fields:

```
curl -v -X POST -d '{"url":"${CLIENT_URL}", "name": "toto"}' -H 'Content-type: application/json' ${SERVER_BASE_URL}/register
```

Notes:

* Obviously, client needs to start a HTTP server able to respond to a `GET` request at the given URL. To check or troubleshoot connectivity, one can use the [netcat](https://linux.die.net/man/1/nc) program to fire up a local server with `nc -l 12345` and use the ip and port to register the client. This will echo in the terminal whatever the _server_ sends
* If URL is not already registered, server accepts the registration (returning a `200 OK` 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`

# NOTES

* [x] make command line to register more explicit
* [x] `nc -l` is a simple echo server to show what's sent by the server
* [x] keep the readme exposed by the server
* [ ] use JSON formatting for request/response
* [ ] debug user address on the leaderboard page
  * [ ] shows status of client (not connected/connected/replying correctly or not)
* [ ] add more logs to server to help troubleshoot users access/registration
* [ ] THE SERVER MUST NOT CRASH
* [ ] cheatsheet λ-calcul exposed on `/help`
* [ ] propose to send JSON or S-Exp
* [ ] persist user state to avoid losing connections
* [ ] deploy automatically server on punkachien.net with radicle CI

* [ ] ask people to implement something
* [ ] prepare starter kit to overcome
* [ ] différentes couleurs de pistes (verte/rouge/noire)
* [ ] pair programming w/ Manu, people do their own stuff if they want
* [ ] ne pas oublier le routeur wifi