clarification regarding backquote query

[Don Morrison <Morrison at UTAH-20>]

The sort of thing I had in mind for a complicated macro producing macro
was to have a macro producing macro foo consing up the final form,  but
bits and pieces it stuffs in are being created by a function bar.   The
value which foo finally  returns will be  some hairy conglomeration  of
conses, lists, and appends, such  as backquote is particularly good  at
creating.  But the pieces  which bar creates  will mostly be  constant,
but sometimes I'd like bar to be able to return a piece which  contains
a call  on unquote,  which  unquote will  be  seen by  the  dynamically
surrounding  backquote  (i.e.   in   foo),  rather  than  a   lexically
surrounding one. Perhaps  this is  too complicated to  be done  clearly
(this description certainly  is so  complicated that I  doubt it  would
ever be clear) with  backquote, but I seem  to remember having  created
such a beast  where this  seemed more  perspicuous than  the hard  way.
Unfortunately I can't remember the exact example, and all the  examples
I can now dream up don't warrant such a procedure; seems that in all my
toy examples simply adding an unquote in the caller and a backquote  in
the callee  works.   Perhaps  the "dynamic  version"  is  never  really
useful.  And anyway, I gather from  some of the replies that there  are
functional entry points to the required pieces available in MACLISP and
friends, though I still don't know their names. 
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