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From: jaxon@sp27.csrd.uiuc.edu (Greg P. Jaxon)
Newsgroups: comp.lang.apl
Subject: Re: brackets
Keywords: brackets indexing axis
Message-ID: <1991Feb28.200918.6276@csrd.uiuc.edu>
Date: 28 Feb 91 20:09:18 GMT
References: <1991Feb23.234505.5960@csi.uottawa.ca> <1991Feb26.210503.2798@yrloc.ipsa.reuter.COM> <6697@idunno.Princeton.EDU>
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> Brackets are anomalous in APL

Indeed their effects on the object to their left are basically left up
to that object.  But I associated one semantic action with the OBJ to [
binding in APLB:  The value of #IO to be used when interpreting the
content of the brackets was picked up at this point.  The limit on RANK
was also applied here (if OBJ was data, ['s could have no more than RANK - 1
semicolons, if OBJ was not data, no semicolons, and value(s) in range for
axis numbers (remember laminate?)) 

The binding of #IO allows an axis specifier to become part of a derived
function and be used in a different #IO binding without changing the
axis being specified.  One advantage of "rank" is that axes aren't numbered,
they are counted!  Does J have a variable #IO, or have we finally been spared
that disaster?