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

> -----Original Message----- > From: marcus.boerger@t-online.de [mailto:marcus.boerger@t-online.de] > Sent: 13 March 2003 19:33 > To: Ford, Mike [LSS] > Cc: 'Andrey Hristov'; php-dev@lists.php.net > 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 --------------------------------------------------------------------- Mike Ford, Electronic Information Services Adviser, Learning Support Services, Learning & Information Services, JG125, James Graham Building, Leeds Metropolitan University, Beckett Park, LEEDS, LS6 3QS, United Kingdom Email: m.ford@lmu.ac.uk Tel: +44 113 283 2600 extn 4730 Fax: +44 113 283 3211