allow method
Implementation
bool allow() {
if (tokens.isEmpty) return true;
Token previous = tokens.last;
return (previous.type == TokenType.EQUAL ||
previous.type == TokenType.LEFT_PAREN) ||
previous.type == TokenType.COMMA ||
previous.type == TokenType.COLON ||
previous.type == TokenType.MINUS ||
previous.type == TokenType.PLUS ||
previous.type == TokenType.STAR ||
previous.type == TokenType.SLASH ||
previous.type == TokenType.PRINT;
}