AC6

This is a school project for the compilation class. The goal is to write an interpreter for Clap, a toy language designed by YRG.

Build with make, run with ./clap <your file>. The code of the project is on Github, the repository will be made public shortly after the due date.

The code has been optimized for speed, and our interpreter has been the fastest one since the beginning of the speed contest. When this is possible, lists are replaced by Hashtbls to improve lookup efficiency, like in Primitive.ml. Several alternatives were explored, such as using a Map for the current environment (this is less efficient than the actual implementation using a list), and several micro-optimizations are done (e.g. using pattern-matching instead of multiple if/else).

Additional Features

Static Type-Checking

With --type, the interpreter statically check if the types in the program are correct, using the Hindley-Milner algorithme.

Memoization & Maximal Sharing

With --memo, the interpreter use memoization and maximal sharing (hash consing). This ensure that a function application is only computed once (the result is stored in the memory), and that a value is only stored once in the memory.

REPL

With -i or --repl, an interactive interpreter is launched. It works like any other REPL. When you give it a definition, it evaluate it in the current environment, and prints its value. It supports multi-lines code, and some special commands:

• /exit, /quit, or ^D: exit the REPL
• /help: print this list of commands
• /clear: clear the current environment

Note that you have to press <enter> on a newline to end your definition.

Additionally, the REPL can be used for debugging purposes. Run ./clap -i with some files, and it will execute each file one by one, then merge their definitions and launch the REPL.

% echo "val x = 42" > a.clap
% ./clap -i a.clap
** Clap REPL v0.2.0
**
** Press ^D to exit.
**
clap> val xx = x * 2
   ?>
:- xx = 84
clap>^D

Debug Mode

A debug mode can be activated using the --debug flag on the command-line. The interpreter will then print debugging informations.

Primitives

One additional primitive has been added, print, which prints its argument. No newline is printed after it.

Bash completion

Source the utils/bash_completion.sh file somewhere in your ~/.bashrc, e.g.:

. /…/AC6/utils/bash_completion.sh

Or, simpler, copy it as /etc/bash_completion.d/clap. It supports options and filenames completion for the clap executable.

Vim syntax highlighting

Run make vim-clap-syntax and follow the instructions. It will add basic syntax support for Clap in Vim.

Tests

To run the tests, use make check. It’ll run the whole tests suit. When the total number of successful tests is greater than the previous one (or if it’s the first time you’re running the tests), fireworks in ASCII art are displayed, and the new highscore is set.

A script, written in Ruby, can be used to generate a few tests from the email answer of the correcting server. It can be found in utils/get_server_tests.rb. Additionally, some dozens of tests has been written by hand, to match some cases which are not not matched by the “official” tests suit.

Known Issues

• The print primitive doesn’t handle special chars, like \n.
• The type checking is not fully implemented.