Re: macro expansion

[Alan Bawden <ALAN at MIT-MC>]

    Date: 24 Nov 1980 21:02:02-PST
    From: CSVAX.fateman at Berkeley

    Why do you say the macros are being mis-used?  If there are no
    incompatibilities when the expansion converges, why not give it a
    better meaning when the expansion does not converge?  

Well I heven't yet accused anyone of mis-using anything since I am
still trying to figure out just what we are talking about.  I am not
sure I can imagine a reasonable interpretation for a divergent macro
expansion other than as an error.  In fact I think I prefer that it
get a PDL overflow so that I can find out that I am losing right away,
rather than waiting untill I grow suspicious waiting for my program
finish.  (It also helps in debugging if macros are expanded
recursively; you can poke back up the stack and look at the original
code before the macro expanded it into a DO with 69 GENSYMed labels...)

							  I asked
    Friedman about compilation, and he said he is not interested in
    that...  As for a clearly USEFUL example, I cannot provide one off
    the top of my head, but you might look at some of Friedman's
    papers, perhaps.  I have no particular stake in this personally.

Anyone who doesn't care about compilation, and who also wants some
peculiar features in his interpreter, is a good candidate for writing
his own interpreter!  My misgivings about munging with the way that
macros are exapanded only extend as far as real-world Lisp programmers
are forced to live with the result.  I am as interested as anyone in
interpreters with unusual and/or theoretically interesting properties.
I have lost count of the interpreters I have written just to see what
it is like to type to a read-eval-print loop with X strange property.
Writing a Lisp interpreter in Lisp is an easy exercise that
practically anyone can do (after all, someone else has already done
the really hard part: written all the subrs!).