Defining macro-variables without a value
From @stepan-a
I have no opinion about the null value (it is an implementation detail that will not affect the user experience). In C macro language I believe it's legal to use the #define statement without assigning a value (and that an error is thrown if one is trying to do something with its value). I really don't like the idea of providing a value to a variable if we only have to test for the existence of the variable in the sequel, and I would prefer to issue an error if the variable is used later for arithmetic or anything else involving its value (I also consider this as safer since the variable is not intended for this, so in this sense the alternative you advocate is not equivalent). We are currently forced to do as you suggest when declaring variables in the .mod files and it is rather ugly...