I'm beginning to come around to the idea that a 'proper' macro processor could be useful, but I'm still struggling to think of good uses for it. Aristotle came up with one, allowing Assert() to provide meaningingful error messages about what failed, particularly useful if the condition being tested has multiple sub-conditions. His example was Assert( A eq B && C eq D); could fail with a message saying "A equaled B but C did not equal D" which could be handy, though a C-style Assert macro that took a text argument for output if the condition failed, used twice could achieve this, Then need to adjust the texts when the conditions change is better handled by the compiler than the programmer.

Can you think of (and preferably pseudo-code:) an application that you would like to use immediately if P5 woke up tomorrow and had grown a macro-processor?