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From: sam@kalessin.jpl.nasa.gov (Sam Sirlin)
Newsgroups: comp.lang.apl
Subject: Re:  "over" and "by"
Message-ID: <1991Jan14.030907.17684@jato.jpl.nasa.gov>
Date: 14 Jan 91 03:09:07 GMT
References: <15160010@hpdmd48.boi.hp.com>
Sender: sam@kalessin.jpl.nasa.gov (Sam Sirlin)
Organization: Jet Propulsion Laboratory, Pasadena, CA
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In article <15160010@hpdmd48.boi.hp.com> rrr@hpdmd48.boi.hp.com (Rudi Rynders) writes:
>
> The  "OVER" and  "BY" constructs mentioned in my previous
> note are defined as follows:
>
>    over =.;@({.;}.)&":@,
>
>    by =.(,~"_1' '&;&;)~
>
>
>  Using these one can neatly produce the result of the APL
...
>  
>  but how this it work?
>
To see how they work, I applied the various operators first. For example
   a over b
is
   a u@v&w@x b   for appropriate verbs u-x
which is equivalent to
   u v w (a x b)
or
   ;({.;}.)":(a,b)
which is easy to understand. Applying this idea to by (a little more subtle)
I get
   a by b
equivalt to
   (' ';;a),"_1 b
which is also much easier for me to comprehend. 

Sam Sirlin
Jet Propulsion Laboratory         sam@kalessin.jpl.nasa.gov




Sam Sirlin
Jet Propulsion Laboratory         sam@kalessin.jpl.nasa.gov