I guess you can dynamically call functions, but function name and parameters must be stored independently, not in one single string. Example:
PHP Code:
functionname = "say2";
functionparam1 = "Hello!";
(@functionname)(functionparam1);
or
PHP Code:
functionandparams = "putexplosion,2,30,30";
(@functionandparams[0])(functionandparams[1], functionandparams[2], functionandparams[3]);
Such stuff should only be done by experienced scripters though, since it can be quite insecure.