You don't. An OpenSCAD program is like a big math equation. x = x + 1 is
illegal because x can't have two values at once.

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I really think we should use 'constant' or some equally descriptive term.
(define value? like #define)?

Bite the bullet, this keeps coming up so often...

But we need to clarify the iterative list comprehension/recursion in
expressions, v's the for() loops/if() in geometry... I think we are
having/approaching a clash of terminology of module geometry instantiation
v's expression evaluation.

Let the battle begin....

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I'm comfortable with calling them variables, but I suppose they could be
called parameters instead. The wikipedia definition suggests that
"parameter" might be appropriate in a mathematical sense:

http://en.wikipedia.org/wiki/Parameter#Mathematical_functions

"Mathematical functions have one or more arguments that are designated in
the definition by variables. A function definition can also contain
parameters, but unlike variables, parameters are not listed among the
arguments that the function takes. When parameters are present, the
definition actually defines a whole family of functions, one for every valid
set of values of the parameters."

The Variable wikipedia page defines parameters as a subclass of variables:

http://en.wikipedia.org/wiki/Variable_%28mathematics%29#Specific_kinds_of_variables

"To distinguish them, the variable x is called a unknown, and the other
variables are called parameters or coefficients, or sometimes constants,
although this last terminology is incorrect for an equation and should be
reserved for the function defined by the left-hand side of this equation."

It also works well with calling OpenSCAD files "parametric designs".
However, "parameters" and "unknowns" are indistinguishable in code (and in a
formula, for that matter), which would make explaining the difference a
little bit more difficult to a naive person: unknowns appear in the argument
list of the function.

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/"You have my objection. They are variables in the mathematical sense. A
symbol that represents a quantity in a mathematical expression."/

I agree with Mr. Peel and cast my vote similarly.

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Every other language without destructive update operator (c-style assign)
calls them variables, I don't see why OpenSCAD should be different.

They aren't "constant", because a constant is a value that never changes.
function square(s) = s*s;
b = 6;
a = square(b);
The variable a's value isn't constant - it changes according to the value of
b.

What's really needed is:

• Giving an error message when trying to redefine a variable.
• Clean up other doubtful cases.
• An explanation for people from procedural programming languages (C-style).
• Push all these changes to release version.

Have a nice day,
Bananapeel :)

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