RE: [sv-bc] [Fwd: Issues with IEEE 1364-2005]

What's an example of the usefulness of C's left-to-right
short-circuiting disjunction?

-- Brad   

-----Original Message-----
From: Will Adams [mailto:wadams@freescale.com] 
Sent: Tuesday, August 15, 2006 6:26 AM
To: Brad Pierce
Cc: sv-bc@eda-stds.org; michael.burns@freescale.com
Subject: Re: [sv-bc] [Fwd: Issues with IEEE 1364-2005]

The `&&&' operator can only appear in limited syntactic contexts. The
following reasonable uses of conjunction are not allowed by the syntax.

   c = a &&& b ;
   if ( ! ( a &&& b ) )

The second of these is a problem because there is no `|||' short
circuiting disjunction, and the syntax does not allow this operation to
be expressed with `!' and `&&&'.

If `&&' is not required to have short-circuit evaluation, and `&&&' is
suggested as an alternative for cases where short-circuiting is desired,
we have a situation where a familiar operator has unfamiliar semantics,
and the familiar semantics are only available in limited contexts from
an unfamiliar operator.

will


Brad Pierce wrote:
>> It sounds like '&&&' is not appropriate to use as a general-purpose
> short-circuit
>> logical AND.
> 
> Because &&& allows the
> 
>      expression 'matches' pattern &&& ...
> 
> syntax, it can do *more* than a general-purpose short-circuit logical 
> AND.  How does its greater generality make it inappropriate for a more

> restrictive purpose?
> 
> Regardless of the original reasons for introducing
> 
>     if (expression &&& expression)
> 
> it behaves exactly like C users have come to expect from
> 
>     if (expression && expression)
> 
> .
> 
> -- Brad
> 
> -----Original Message-----
> From: Steven Sharp [mailto:sharp@cadence.com]
> Sent: Monday, August 14, 2006 2:43 PM
> To: Brad.Pierce@synopsys.COM; nikhil@bluespec.com
> Cc: wadams@freescale.com; sv-bc@eda-stds.org; 
> michael.burns@freescale.com
> Subject: Re: [sv-bc] [Fwd: Issues with IEEE 1364-2005]
> 
> 
>> From: "Rishiyur Nikhil" <nikhil@bluespec.com>
> 
>> '&&&' is not merely a conjunction operator, and its reason for 
>> existence is not to introduce short-circuiting-- it is because it has

>> a
> 
>> variable-binding function unique to the pattern-matching facilities 
>> of the language.
> 
> Thanks for the explanation.  It sounds like '&&&' is not appropriate 
> to use as a general-purpose short-circuit logical AND.
> 
> Steven Sharp
> sharp@cadence.com
> 
>