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

Well, *avoiding* the side effect of a crash is a good thing.

I think everyone agrees that this functionality can be had in
various ways.

The point is that short-circuiting is a long and established
practice in programming.  Experienced C programmers rely on
it all the time, and it's easy to read other people's code
that relies on it.  Reading the ternary operator example
is tougher... I had to study it a bit to see what was
going on.

If SystemVerilog establishes short-circuiting in a way
consistent with C, it will help adoption and appreciation
of the language by most users.

Does anyone else dissent to establishing conventional
short-circuiting behavior for || and && besides Brad?

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 1:04 PM
> To: sv-bc@server.eda-stds.org
> Subject: 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
> > > 
> > > 
> > 
> > 
> 
>