Newsgroups: comp.lang.apl
Path: utzoo!utgpu!news-server.csri.toronto.edu!torsqnt!tmsoft!itcyyz!yrloc!rbe
From: rbe@yrloc.ipsa.reuter.COM (Robert Bernecky)
Subject: Re: APL, J syntax descriptions; PD software
Message-ID: <1991May17.215146.27807@yrloc.ipsa.reuter.COM>
Keywords: APL, J, PD, manual, texts, compilers
Reply-To: rbe@yrloc.ipsa.reuter.COM (Robert Bernecky)
Organization: Snake Island Research Inc, Toronto
References: <129234@unix.cis.pitt.edu>
Date: Fri, 17 May 91 21:51:46 GMT

In article <129234@unix.cis.pitt.edu> mgkst1@unix.cis.pitt.edu (Michael G Koopman) writes:
>
>Are there any compilers for APL variants?  If not what makes a compiler
>for APL so difficult?  With the almost advent of Fortran 90 is anyone
>considering these compiler designs with respect to APL designs?

Tim Budd has a free APL compiler, written as a university project.

STSC offered an APL compiler, but I believe they no longer actively
(or at all??) market it.

Recent rumour suggests that someone has obtained rights to distribute
YAT (Yorktown Apl Translator (apl to Fortran)), written at IBM's T.J.
Watson Labs.

I am working on a J compiler. Stay tuned.

Why is an compiler so difficult? Partially because it was common
knowledge that it was nearly impossible. Once that belief got walked
on, it became less hard. 

More seriously, the major problems of compiling APL to get more speed
(I presume that's the major reason you'd want to compile it) are
things like:

a. Dynamic scoping rules. You need to examine the entire possible calling
]  tree.

b. execute, function fix, function expunge, and similar goodies.

c. Ability for arrays to change type, rank, and shape underfoot.

However, even a naive compiler won't do bad on certain problems in
which large arrays are being used. See Bernecky, et al., in APL90
(Acorn: APL to C on Real Numbers). A toy compiler did about half as
good as hand-unrolled Fortran on real seismic problems.

Robert Bernecky      rbe@yrloc.ipsa.reuter.com  bernecky@itrchq.itrc.on.ca 
Snake Island Research Inc  (416) 368-6944   FAX: (416) 360-4694 
18 Fifth Street, Ward's Island
Toronto, Ontario M5J 2B9 
Canada