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From: rockwell@socrates.umd.edu (Raul Rockwell)
Newsgroups: comp.lang.apl
Subject: the difference between f : '' and f@]
Message-ID: <ROCKWELL.91Jun6222025@socrates.umd.edu>
Date: 7 Jun 91 03:20:25 GMT
Sender: rockwell@socrates.umd.edu (Raul Rockwell)
Organization: Traveller
Lines: 28

I used f :'' and f@] in my last post, and it's been bugging me that I
didn't make clear what the difference was (or what they have in
common).  By the way, the space, in (f :''), is necessary -- even
though I said f:'' in my other post...

Let  f  represent some J verb.  Then,
  f :'' x
and
  f@] x
and
  f x
should give you the same result.  But both of the derived verbs have
infinite rank, which can be important when using them to construct
other verbs.

However,
  x f :'' y
gives a domain error, while
  x f@] y
gives the same result as  f@] y


There, how's that?  A post which is probably totally incomprehensible
to someone not familiar with J, and probably totally obvious to an
experienced J programmer....  I hope somebody gets some use out of
this.

Raul Rockwell