RE: [PHP-DEV] Possible problem in the parser

[Andi Gutmans]

You are right that it doesn't behave the same as C. However, personally 
although it might have been better for it to work like C I don't think it's 
a good idea to change it now. First of all it would break backwards 
compatibility in a way which would be hard for people to find where the bug 
is and how to fix it. Secondly, not meaning to insult anyone here, but I 
think people who write such code without using parentheses should improve 
their coding style :)

Andi

At 12:01 PM 3/14/2003 +0000, Ford, Mike               [LSS] wrote:
> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
> Sent: 13 March 2003 19:33
> To: Ford, Mike [LSS]
> Cc: 'Andrey Hristov'; [EMAIL PROTECTED]
> Subject: RE: [PHP-DEV] Possible problem in the parser
>
>
> At 14:58 13.03.2003, Ford, Mike               [LSS] wrote:
>
> >Just to make this completely clear, in left-associative PHP
> >
> >    b = a==1? 4:a==2? 5:6;
> >
> >is equivalent to
> >
> >    b = (a==1? 4:a==2)? 5:6;
>
>
> NO it is not equal. Either '==' has higher precedence OR '?:' has.
> See one of my previous mails where i showed where the error is.
Yes, it is -- believe me, I've researched this extensively.  It is NOT 
about precedence, but associativity.  If you want me to be totally 
completist about this:

Starting from:

   b = a==1? 4:a==2? 5:6;

precedence rules make this equivalent to:

   b = (a==1)? 4:(a==2)? 5:6;

but this is still ambiguous -- which ?: phrase do you evaluate 
first?  Associativity provides the answer: in PHP, where ?: is left 
associative (i.e. the left most ?: is evaluated first), the result is 
equivalent to:

   b = ((a==1)? 4:(a==2))? 5:6;

On the other hand, in c, where ?: is right associative, the equivalent is:

   b = (a==1)? 4:((a==2)? 5:6);

which, apart from the additional (unnecessary) parentheses around the == 
comparisons, is exactly what I said before.

QED

Cheers!

Mike

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Mike Ford,  Electronic Information Services Adviser,
Learning Support Services, Learning & Information Services,
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