Sphpeme

A dumb slow Scheme running inside php

Usage

The file sphpeme.php is autoloaded, so all the functions therein there are available.

Example

<?php

use Sphpeme\EnvExtender\AggregateEnvExtender;
use Sphpeme\ExpHandler\DefineExpHandler;
use Sphpeme\ExpHandler\IfExpHandler;
use Sphpeme\ExpHandler\LambdaExpHandler;
use Sphpeme\ExpHandler\LetHandler;
use Sphpeme\ExpHandler\LetStarHandler;
use Sphpeme\ExpHandler\NamedLetHandler;
use Sphpeme\ExpHandler\ScalarHandler;
use Sphpeme\ExpHandler\SymbolHandler;
use Sphpeme\Reader;

require __DIR__ . '/vendor/autoload.php';

$env = new \Sphpeme\Env\StdEnv();
$reader = Reader::fromFilepath(__DIR__ . '/fib.scm');
$parsedLib = $reader->read();

// Evaluator with ORDERED expression handlers
$eval = new \Sphpeme\Evaluator(
    new SymbolHandler(),
    new ScalarHandler(),
    new LambdaExpHandler(new AggregateEnvExtender()),
    new IfExpHandler(),
    new DefineExpHandler(),
    new NamedLetHandler(),
    new LetHandler(),
    new LetStarHandler()
);

// Evaluate the library, adding its definitions to our env
$eval($parsedLib, $env);

$fakeInput = '(fib 15)';
$fake = fopen('php://memory', 'w+b');
fwrite($fake, $fakeInput);
rewind($fake);
// Evaluate some other code, which uses the updated env
$program = Reader::fromStream($fake)->read();
$time = microtime(true);
$eval($program, $env);
echo microtime(true) - $time;

Tests

Near all of sphpeme.php is covered by tests. Tests can be run by calling phpunit after comoposer installation:

$ ./vendor/bin/phpunit

Todo

Speed

While it's unlikely that sphpeme will ever exist outside the context of "toy," faster is better! Evaluation and tokenization are two areas ripe for improvement.

Ideas

• Fewer function calls
• "Flattener" for envs, eliminating linear search for a match

Features

letrec

With the addition of let* and let, many local definition needs are covered.

cond

Better than nested if!!!

m-m-m-macros!

maybe.

Credits

Much of the work here is simply a translation of Peter Norvig's excellent article, (How to Write a (Lisp) Interpreter in(Python))