In a RecDescent grammar, I'd like to add support in my language for "macros".
These macros would be very much like #define macros in C and would support arguments that are instantiated into the expansion. In C, this looks something like: 
#define   add(a,b)        (a+b)

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In my language, I'd like something like: 
myMacro(x,y):        any_expression

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where "any_expression" is any old (deep) expression defined elsewhere in the grammar, and (x,y) would be replaced/instantiated in that expression.

This may seem straighforward, but, well, it ain't to me. (I am, after all, mush4brains.)
In my P::RD grammar, the "macro" rule without arguments would look like: 
macro:         identifier ':' expr

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where, again, expr is defined fully in the grammar. Adding arguments to this... I need to instantiate my (x,y) into the "expr" string before the subrules interpret it.

Now... I thought of using standard Perl substitution in a pre-scan, but this seems less-than-ideal, since it requires some knowledge of the grammar in the Perl REs.

I thought of using two separate grammars, the first of which is a simplified version of the full second grammar, but this also seems a bit redundant.

Then I thought... "This hurts".
And then... "Hey, I'll ask the Monks!!!"

So... what am I missing here? Something obvious, I imagine?

Thanks for any help.
Jim Wiltshire

In reply to Macros in a RecDescent grammar by mush4brains

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