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From:         eem@ipsaint.ipsa.reuter.COM (Mcdonnell, Eugene E.)
Subject:      reply to Emmett McLean
Message-ID: <1992Dec23.032519.29526@yrloc.ipsa.reuter.COM>
Sender: intern@yrloc.ipsa.reuter.COM (Intern via QUADRAM)
Reply-To:     eem@ipsaint.ipsa.reuter.COM (Mcdonnell, Eugene E.)
Organization: Reuters Information Services (Canada)
Date:         23 Dec 92 03:00:06 UT
Lines: 65


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no. 6849643 filed  2.53.22  wed 23 dec 1992
from eem
to   uclapl
subj reply to Emmett McLean


.In reply to Emmett McLean's inquiry for details of >!._ and u^:g
 and g} :

 A. To understand >!._ you should know that z=. <!.n y for any
 nouns n and y is an atomic encoding of y having class n, so that
 >!._ z is n.  For example,
    y=.123 45 6789
    n=.'social security number'
    z=. <!.n y
    >!._ z
 social security number

 Thus the two verbs <!.n and >!._ allow a noun to be enrolled in
 an arbitrary class n, and for the class of a noun to be
 determined, respectively.  It's not OOP but it has something of
 that flavor.  These are described in J Dictionary Version 5.  

 B. For verbs v0, v1, and v2, and gerund g=.v0`v1`v2, and nouns x
 and y, 
            g} y 
 is defined as 
                     (  v1 y) } (  v2 y)
 and
          x g} y
 is defined as
            (x v0 y) (x v1 y) } (x v2 y)

 Also, for verb f,
       f ^: g y
 is defined as
                f ^: (  v1 y)   (  v2 y)
 and
     x f ^: g y
 is defined as
       (x v0 y) f ^: (x v1 y)   (x v2 y)

 A one- or two-element g is permitted, and expands to 3&$&.|.g. 

 Thus the two forms u^:g and g} are designed to allow a greater
 number of verbs to be specified tacitly than was heretofore
 possible.  Recall section B. of the Hui/Iverson/McDonnell paper
 "Tacit Definition" in APL91 Conference Proceedings (page 204),
 where the translation from explicit to tacit form is permitted
 for a sentence s on nouns x and y provided that s makes no use of
 x or y as argument to an adverb or conjunction.  These two new
 forms provide a way around that restriction for the amend adverb
 } and the power conjunction ^:.  



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