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

Note that in this example, there are no side-effects in the disjunction.


Also, I don't see the big advantage of || vs. ?:.

        contextList = findContext(scope, name, flags, &remainder);
        if ( contextList ? remainder[0] != '\0' : FALSE ) {

             ...

-- Brad

-----Original Message-----
From: Warmke, Doug [mailto:doug_warmke@mentor.com] 
Sent: Tuesday, August 15, 2006 12:42 PM
To: Brad Pierce; sv-bc@eda-stds.org
Subject: RE: [sv-bc] [Fwd: Issues with IEEE 1364-2005]

Of all the things, I just took advantage of this while writing some code
yesterday:

        contextList = findContext(scope, name, flags, &remainder);
        if (!contextList || remainder[0] != '\0') { 
             ...

"remainder" is not initialized if the function returns NULL.
So I don't want to dereference it with [0] in that case.
C's short-circuiting disjunction guarantees this won't happen.

Regards,
Doug


> -----Original Message-----
> From: owner-sv-bc@server.eda-stds.org 
> [mailto:owner-sv-bc@server.eda-stds.org] On Behalf Of Brad Pierce
> Sent: Tuesday, August 15, 2006 12:28 PM
> To: sv-bc@server.eda-stds.org
> Cc: michael.burns@freescale.com; wadams@freescale.com
> Subject: 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
> > 
> > 
> 
>