Path: utzoo!mnetor!uunet!husc6!cmcl2!brl-adm!adm!4526P%NAVPGS.BITNET@CUNYVM.CUNY.EDU
From: 4526P%NAVPGS.BITNET@CUNYVM.CUNY.EDU (LT Scott A. Norton, USN)
Newsgroups: comp.lang.pascal
Subject: Re: Pascal User Manual and Report
Message-ID: <11917@brl-adm.ARPA>
Date: 19 Feb 88 20:43:41 GMT
Sender: news@brl-adm.ARPA
Lines: 39

I don't have the actual ISO Pascal standard, but the ISO/DIS 7185 draft
standard has this to say:
-----------------------------------------------------------------------
  6.7.2 Operators
   6.7.2.1 General

      multiplying-operator = "*" | "/" | "div" | "mod" | "and" .
      adding-operator = "+" | "-" | "or" .
      relational-operator = "=" | "<>" | "<" | ">" | "<=" | ">=" | "in".

A factor, or a term, or a simple-expression shall be deignated an operand.
The order of evaluation of the operand of a dyadic operator shall be
implementation-dependent.
NOTE: This means, for example, that the operands may be evaluated in
textual order, or in reverse order, or in parallel or they may not
both be evaluated.
-------------------------------------------------------------------------
I was surprised to read this, because it does not apply to just "and"
and "or".  It would be legal to handle the expression

  a := b * SideEffect(c);

so that SideEffect(c) is not evaluated if b is zero.

It should be noted that Ada has very explicit rules about the order of
evaluation and what optimizations can be made.  In particular, Ada has
two constructs for each of "and" and "or":

"and" will evaluate both operands, "and also" will evaluate the second
only if the first is true.  Similarly, "or" evaluates both, but "or else"
evaluate the second only if the first is false.  So you can use the
construct

   if ( p<>nil ) and also ( p@.data = target ) then ...

LT Scott A. Norton, USN
Naval Postgraduate School
Monterey, CA 93943-5018
4526P@NavPGS.BITNET   4526P@NPS.ARPA