[mercury-users] lisp macros

[Peter Schachte]

On Thu, May 30, 2002 at 05:00:29PM +1000, Michael Day wrote:

> Wouldn't it be difficult for the compiler to parse a module that contained
> macros that acted on that module itself?

Parse, no, but sometimes it is difficult to write a module that
expands source code in such a way that it can successfully expand
itself.  I often use a trick to ensure that my term_expansion clauses
are not applied to the module that defines them.  In fact, if the
Prolog system removes the old definition of a predicate before
compiling the new one, then much of the time when compiling your
own term_expansion module, the expansion code in memory will be
incomplete.

> Would it be necessary to define
> macros in one module to use them in another? That way the macro module
> could be compiled and then executed by the compiler on the second
> module...

I think that is the most sensible solution to this problem.  For a
system that supplies only a source-to-binary compiler, it will not be
possible to compile a file that defines expansion clauses that are
meant to be run on itself:  you would need to have compiled the file
before you could compile the same file.

-- 
Peter Schachte              That government is best which governs least.
schachte at cs.mu.OZ.AU            -- Thomas Jefferson 
www.cs.mu.oz.au/~schachte/  
Phone: +61 3 8344 9166      
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