First of all: http://www.youtube.com/watch?v=z5jKMEB4hHE
On Wed, Feb 29, 2012 at 12:09:16AM -0800, Xah Lee wrote: > Now, let me tell you what operator precedence is. First of all, let's > limit ourselfs to discuss operators that are so-called binary > operators, which, in our context, basically means single symbol > operator that takes it's left and right side as operands. Now, each > symbol have a “precedence”, or in other words, the set of operators > has a order. (one easy way to think of this is that, suppose you have > n symbols, then you give each a number, from 1 to n, as their order) > So, when 2 symbols are placed side by side such as 「3 △ 6 ▲ 5」, the > symbol with higher precedence wins. Another easy way to think of this > is that each operator has a stickiness level. The higher its level, it > more sticky it is. You're absolutely correct. > the problem with the perl explanations is that it's one misleading > confusion ball. It isn't about “left/right associativity”. It isn't > about “evaluates from left to right or right to left”. Worse, the word > “associativity” is a math term that describe a property of algebra > that has nothing to do with operator precedence, yet is easily > confused with because it is a property about order of evaluation. (for > example, the addition function is associative, meaning: 「(3+6)+5 = > 3+(6+5)」.) You're not getting it. Math is a language. Perl is a language. They have different rules for grammar. In Perl, C, Python, Java, and pretty much all procedural-based languages, operations are evaluated in two steps: the precedence /and/ the associativity. Each level of precedence has its own associativity, either left-to-right or right-to-left. You can see this in table 2-1 in The C Programming Language. Whatever math does or what you think math does has nothing to do with the way Perl evaluates expressions. -- http://mail.python.org/mailman/listinfo/python-list
