Re: internals Digest 23 Nov 2013 00:01:03 -0000 Issue 3138

The Wikipedia page on Operator associativity, at http://en.wikipedia.org/wiki/Operator_associativity, says the following: Associativity is only needed when the operators in an expression have the same precedence. Usually + and - have the same precedence. Consider the expression 7 - 4 + 2. The result could be either (7 - 4) + 2 = 5 or 7 - (4 + 2) = 1. The former result corresponds to the case when + and - are left-associative, the latter to when + and - are right-associative. In order to reflect normal mathematical usage, addition, subtraction, multiplication, and division operators are usually left-associative while an exponentiation operator (if present) is right-associative. Any assignment operators are also typically right-associative. To prevent cases where operands would be associated with two operators, or no operator at all, operators with the same precedence must have the same associativity. Walter ---------- Forwarded message ---------- > > From: Sherif Ramadan <theanomaly.is@gmail.com> > To: Jakub Zelenka <bukka@php.net> > Cc: Nikita Popov <nikita.ppv@gmail.com>, Tjerk Meesters <tjerk.meesters@gmail.com>, > PHP Internals <internals@lists.php.net> > Date: Fri, 22 Nov 2013 19:00:59 -0500 > Subject: Re: [PHP-DEV] Power function as operator > On Fri, Nov 22, 2013 at 6:59 PM, Jakub Zelenka <bukka@php.net> wrote: > > > Hi, > > > > > >> I'm not entirely sure that making it non-associative is a great idea > >> either, but I have to agree that it does find *some* middle ground. > >> Right-associative exponent operator didn't seem right to me either. > >> > > > > I think there is a good mathematical reason for right associative > > exponent. It calls tetration or power tower. Please look at following > > sources for more details: > > > > http://math.stanford.edu/circle/notes08f/bignumbers.pdf > > http://en.wikipedia.org/wiki/Tetration > > http://mathworld.wolfram.com/PowerTower.html > > > > Regards > > > > Jakub > > > > > Right, that would be why I'm not *entirely* convinced. > -- The greatest dangers to liberty lurk in insidious encroachment by men of zeal, well-meaning but without understanding. -- Justice Louis D. Brandeis