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by jazzturk (Novice)
on Oct 27, 2000 at 08:18 UTC ( #38772=CUFP: print w/replies, xml ) Need Help??

I just finished writing a dynamically-scoped Lisp interpreter in Perl. Don't hate me. I couldn't help myself. URI is in my .sig below:

James Bailie

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RE: Lisp-In-Perl
by runrig (Abbot) on Oct 31, 2000 at 00:55 UTC
    Well, comparing your 'Lisp' interpreter against 'perl-lisp' in CPAN (lisp), I have to say that your's is a more complete implementation, and I think the more correct one. On this simple script:
    >(set 'a (list 1 2 3)) Both return: (1 2 3) #Right! >(cdr a) perl-lisp returns: 3 #Wrong! Lisp returns: (2 3) #Right!
    So yours wins here. I think this is because perl-lisp implements lists (1 2 3) as an array instead of an actual linked list (even though when you use 'cons' it seems to construct a proper list), so there is no real way for it to return what its supposed to. Sure, it (perl-lisp) could either shift the array, or take a list slice (which copies the array), but neither is a correct implementation of a list.

    Sorry to say, though, that neither lisp's will execute my favorite Lisp function:
    (defun transpose (x) (apply 'mapcar (cons 'list x)) Which on this input: (transpose '((1 2 3) (4 5 6) (7 8 9) (10 11 12))) Should product this output: ((1 4 7 10) (2 5 8 11) (3 6 9 12))
    This is because neither lisp's implement the apply function, perl-lisp doesn't implement the mapcar function, and I don't think your Lisp correctly implements mapcar, because mapcar should accept any number of lists following the function, but yours only accepts one, and I think (not sure here, its been awhile since I've really done lisp) that you should have to quote the function passed in. (Every once in a while, I've thought that perl should have a mapcar function also :)

    Neither have an append function, either. I would think that appending lists is something a list processing language ought to be able to do :-)
    One thing in perl-lisp's favor, it does have a setq function, which your's lacks, but of course is a trivial thing and should be easy to implement if you wanted to :)

    One more thing you might want to consider is using h2xs to create a normal installable perl module (where you can make/make test/make install), with some tests, like the CPAN modules, and then consider putting this on CPAN.

    I've been looking at the syntax for Common Lisp and it seems I was wrong about mapcar. In Common Lisp it does only take one list argument, so this implementation of mapcar is not an incorrect one, just not a very good one (as is Common Lisp's).
RE: Lisp-In-Perl
by elwarren (Curate) on Oct 30, 2000 at 04:57 UTC
    This is just wrong :-)

    LISP=Lisp InSide Perl
    LISP=Lisp Isn't Supposed to be in Perl
    PERL=Perl Even Runs Lisp
RE: Lisp-In-Perl
by merlyn (Sage) on Oct 27, 2000 at 10:44 UTC

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