private function compileExpression(AST\Node $expression) : string
{
if ($expression instanceof AST\Constant) {
return var_export($expression->getValue(), true);
} else {
if ($expression instanceof AST\Variable) {
return '$' . $expression->getName();
} else {
if ($expression instanceof AST\Operator) {
$operatorTemplate = OPERATORS[$expression->getKind()]['expression'];
$leftString = $this->compileExpression($expression->getLeftOperand());
$rightString = $this->compileExpression($expression->getRightOperand());
$string = preg_replace(['/\\$a/', '/\\$b/'], [$leftString, $rightString], $operatorTemplate);
return '(' . $string . ')';
} else {
if ($expression instanceof AST\FunctionCall) {
$argumentStrings = array_map([$this, 'compileExpression'], $expression->getArguments());
$string = FUNCTIONS[$expression->getName()]['phpFunction'] . '(' . implode(',', $argumentStrings) . ')';
return $string;
} else {
throw new \Exception("Unexpected node type: {getclass({$expression})}");
}
}
}
}
}
public function evaluate(AST\Node $expression, array $environment) : float
{
if ($expression instanceof AST\Constant) {
return $expression->getValue();
} else {
if ($expression instanceof AST\Variable) {
if (!isset($environment[$expression->getName()])) {
throw new \Exception("'{$expression->getName()} must be defined!");
}
return $environment[$expression->getName()];
} else {
if ($expression instanceof AST\Operator) {
static $cachedOperators = [];
if (!isset($cachedOperators[$expression->getKind()])) {
$operatorFunction = create_function('$a, $b', 'return ' . OPERATORS[$expression->getKind()]['expression'] . ';');
$cachedOperators[$expression->getKind()] = $operatorFunction;
} else {
$operatorFunction = $cachedOperators[$expression->getKind()];
}
$left = $this->evaluate($expression->getLeftOperand(), $environment);
$right = $this->evaluate($expression->getRightOperand(), $environment);
return $operatorFunction($left, $right);
} else {
if ($expression instanceof AST\FunctionCall) {
$arguments = array_map(function ($argument) use($environment) {
return $this->evaluate($argument, $environment);
}, $expression->getArguments());
return FUNCTIONS[$expression->getName()]['phpFunction'](...$arguments);
} else {
throw new \Exception("Unexpected node type " . get_class($expression));
}
}
}
}
}
