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))

mattwellss/sphpeme