ftp.cs.arizona.edu/ftp.cs.arizona.edu.tar/ftp.cs.arizona.edu/icon/newsgrp/group96a.txt/000065_icon-group-sender _Wed Mar 6 15:09:39 1996.msg

Internet Message Format | 1996-09-05 | 2KB

Received: by cheltenham.cs.arizona.edu; Wed, 6 Mar 1996 12:20:41 MST
From: "Hamish Lawson" <[e-mail]>
Organization:  University of Teesside (SCM)
To: [e-mail]
Date:          Wed, 6 Mar 1996 15:09:39 GMT0BST
Subject:       Re: Production of an operator's left-hand operand
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Status: O

I've been trying to make a case for a parallel set of operators that
that produce their left-hand side. The example I chose was of
printing the result of some expression only if a subsequent
expression succeeds. It's been pointed out that this can be achieved
thus:

   write(1(e1,e2))

It's my own fault for choosing a poor example. Ken Walker did
concede that there is not an equivalent for comparison operators.
Let's choose a better (I hope!) example: say I want to print out
expression e1 only if its value is less than e2. The order of
evaluation may be important and so

   write(e2 > e1)

may not be possible. We're forced to the rather inelegant alternative

   write((e1 < (temp := e2), temp))

(The temp variable is necessary in the general case because a sceond
evaluation of e2 may produce a new value.)

Thus my proposal of an alternative set of operators that produce
their RH operands (I suggested prefixing the standard operators with
^); our expression then becomes

   write(e1 ^< e2)


| Hamish Lawson, School of Computing and Mathematics,
| University of Teesside, Middlesbrough, Cleveland, UK, TS1 3BA
| Tel: [phone] x3611  Fax: [phone]
| E-mail: [e-mail]