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From:         eem@ipsaint.ipsa.reuter.COM (Mcdonnell, Eugene E.)
Subject:      adverse in J
Message-ID: <1993Jan10.053316.18324@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:         10 Jan 93 05:00:05 UT
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-----------Message forwarded from IPSA Mailbox-------------


no. 6889070 filed  4.54.37  sun 10 jan 1993
from eem
to   uclapl
subj adverse in J

  

Paul Moore (pmoore@cix.compulink.co.uk). asks what the meaning of 
u :: v is.  It is related to obverse, in the sense that either u 
or v is executed.  In fact, u :: v y is u y unless circumstances 
are adverse to u's successful execution, in which case the 
"adverse" verb v is executed.  Similarly for x u :: v y.  

The motivation for this language facility is to reduce the 
occasions when quoted strings are required in J.  Compare it with 
"do left if error" (".), whose arguments are required to be 
character lists, with all the resulting nastinesses familiar to 
those who have used the execute primitive in APL systems -- or 
the execute alternate system function in APL2. 


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