/**
* Function that evaluates a given syntax tree
* @param array $params
* @param array $env Environment to be used
* @return mixed Result
*/
public function evaluate($params)
{
if (is_numeric($params)) {
return (double) $params;
} elseif (is_string($params)) {
$ret = Common::findInEnv($this->env, $params);
if ($ret === Common::NONE) {
throw new Exception("undefined atom {$params}");
} else {
return $ret;
}
} elseif (!is_array($params)) {
return $params;
} elseif ($params[0] == 'quote') {
if (count($params) != 2) {
throw new Exception("bad syntax for quote");
}
return $params[1];
} elseif ($params[0] == 'lambda') {
if (count($params) != 3) {
throw new Exception("bad syntax for lambda");
}
$parms = $params[1];
$body = $params[2];
$env = $this->env;
return function ($args) use($parms, $body, $env) {
$newEnv = new Environment(Common::zip($parms, $args));
$x = new TinyLisp(array($newEnv, $env));
return $x->evaluate($body);
};
} elseif ($params[0] == 'if') {
if (count($params) != 4) {
throw new Exception("bad syntax for if");
}
$ret = $this->evaluate($params[1]) ? $this->evaluate($params[2]) : $this->evaluate($params[3]);
return $ret;
} elseif ($params[0] == 'define') {
if (count($params) != 3) {
throw new Exception("bad syntax for define");
}
$multiple_scoped = false;
foreach ($this->env as $key => $value) {
if ($value instanceof Environment) {
$multiple_scoped = true;
break;
}
}
$param = is_array($params[2]) ? $this->evaluate($params[2]) : $params[2];
if ($multiple_scoped) {
// multiple scopes, apply this only to the top most
$this->env->v[0][$params[1]] = $param;
} else {
$this->env->v[$params[1]] = $param;
}
} elseif ($params[0] == 'print') {
if (count($params) != 2) {
throw new Exception("bad syntax for print");
}
print_r($this->evaluate($params[1]));
} else {
$proc = $this->evaluate($params[0]);
$args = array();
// for (define first car), $proc may return 'car', in which case we need to re-evaluate
if (is_string($proc)) {
array_shift($params);
return $this->evaluate(array_merge(array($proc), $params));
}
for ($i = 1; $i < count($params); $i++) {
$args[] = $this->evaluate($params[$i]);
}
if (is_callable($proc)) {
return $proc($args);
} elseif (is_array($proc) && method_exists($proc[0], $proc[1])) {
return call_user_func_array($proc, array($args));
} else {
throw new Exception("Can't parse " . print_r($params, true));
}
}
}
