private static function validateTokens($tokenStream)
{
// No return value --- throws exception when error encountered.
$stack = array();
for ($i = 0; $i < count($tokenStream); $i++) {
$node = $tokenStream[$i];
switch ($node->type) {
case ExpType::$TERNARY:
// drop through
// drop through
case ExpType::$PAREN:
// Check balance
if (in_array($node->value, ExpLexer::$ENDS)) {
$stackLeft = array_pop($stack);
if (ExpLexer::$PAIRS[$node->value] != $stackLeft) {
throw new ExpLexerException("Unbalanced expression");
}
} else {
array_push($stack, $node->value);
}
break;
case ExpType::$UNARY_OP:
// Check unary operator gramma
if (!ExpLexer::hasUnaryLeft($tokenStream, $i)) {
throw new ExpLexerException("Mal-format unary operator");
}
break;
case ExpType::$BINARY_OP:
// Check binary operator gramma
if (ExpLexer::hasUnaryLeft($tokenStream, $i) || !ExpLexer::hasBinaryRight($tokenStream, $i)) {
throw new ExpLexerException("Mal-format binary operator");
}
break;
case ExpType::$DOT:
// Check dot gramma
if ($i == count($tokenStream) - 1 || $tokenStream[$i + 1]->type != ExpType::$IDENTITY) {
throw new ExpLexerException("Mal-format dot");
}
break;
case ExpType::$FUNCTION:
// Check function gramma
if ($i == count($tokenStream) - 1 || $tokenStream[$i + 1]->value != '(') {
throw new ExpLexerException("Mal-format function");
}
break;
}
}
if (count($stack) != 0) {
throw new ExpLexerException("Unbalanced expression");
}
}
