An alternative, and perhaps a not so good procedural coding one, is to send the "function name" to a script that then executes the function. For instance, with a login form, there is typically the login, forgotusername, forgotpassword, signin activities that are presented on the form as buttons or anchors. All of these can be directed to/as, say,
weblogin.php?function=login
weblogin.php?function=forgotusername
weblogin.php?function=forgotpassword
weblogin.php?function=signin
And then a switch statement on the receiving page does any prep work and then dispatches or runs the (next) specified function.