MaplePrimes - answers and comments on Question, parameter gymnastics

non-matching default values

Joe Riel — Fri, 11 Mar 2011 20:40:56 Z

For newer releases of Maple you can assign a default value that is different from the declared type and use that to determine whether an argument has been passed. Here NULL might be appropriate

proc( ...  S :: symbol := NULL, L :: list := [], ... )
    if S = NULL then <do something> end if;

unassigning NULL

tijgertron — Mon, 14 Mar 2011 12:06:43 Z

Ah, but suppose I use S in the sequel, and that the user has not specified the symbol. In that case, S should simply be used in its place, but now it's been assigned NULL. Without unassigning it, I cannot use it. However, unassign('S') obviously leads to an error. Any ideas?

non-ambiguity

Axel Vogt — Mon, 14 Mar 2011 13:19:12 Z

Even if it might be done: why should it be done?

Why not simply provide to routines, say procList and procSymbol ...

In that case the user sees what to use as input

ease of use

tijgertron — Mon, 14 Mar 2011 13:56:26 Z

Because then it would just be a required parameter, and I want to remove as much of the complexity of the application as possible. More 'advanced' users might want to give their own symbols to certain parameters, but maybe not the average user.

Apart from that, though, there is the problem that the user is only allowed to specify one, because they cannot be used both at the same time in the procedure. Trying to specify both should give an error but when I have them both as ordered required parameters then it seems rather silly to produce an error.

solution

tijgertron — Mon, 14 Mar 2011 16:18:23 Z

Of course I can create an if-then procedure, where I handle all cases separately, even though that means repeating some of the code. It's not very fancy, but it gets the job done.

suggestion

Joe Riel — Mon, 14 Mar 2011 18:31:42 Z

Is this what you want:

proc( ...  S :: symbol := ':-S', L :: list := [], ... )
...
end proc