Checks the number of parameters of the function. This method is called during the parsing of the equation to check syntax. Functions which set numberOfParameter=-1 should overwrite this method.

Returns the number of required parameters, or -1 if any number of parameters is allowed.

Run the function on the stack. Pops the arguments from the stack, and pushes the result on the top of the stack.

Sets the number of current number of parameters used in the next call of run(). This method is only called when the reqNumberOfParameters is -1.