13.6 Common Problems Using Macros

The basic facts of macro expansion have counterintuitive consequences. This section describes some important consequences that can lead to trouble, and rules to follow to avoid trouble.

13.6.1 Wrong Time		Do the work in the expansion, not in the macro.
13.6.2 Evaluating Macro Arguments Repeatedly		The expansion should evaluate each macro arg once.
13.6.3 Local Variables in Macro Expansions		Local variable bindings in the expansion require special care.
13.6.4 Evaluating Macro Arguments in Expansion		Don't evaluate them; put them in the expansion.
13.6.5 How Many Times is the Macro Expanded?		Avoid depending on how many times expansion is done.