Re: New Science Discovery: Perl Idiots Remain Idiots After A Decade!New Science Discovery: Perl Idiots Remain Idiots After A Decade!
On 3/12/2012 20:00, Albert van der Horst wrote: [...] Sorry for triple posting. I hadn't noticed the follow up and I was blaming my newsserver. BTW, Python is the next language (right after Perl) I'm going to learn. Then I'll probably have a look at Ruby... Kiuhnm -- http://mail.python.org/mailman/listinfo/python-list
Re: New Science Discovery: Perl Idiots Remain Idiots After A Decade!New Science Discovery: Perl Idiots Remain Idiots After A Decade!
On 3/12/2012 20:00, Albert van der Horst wrote: In article<4f5df4b3$0$1375$4fafb...@reader1.news.tin.it>, Kiuhnm wrote: On 3/12/2012 12:27, Albert van der Horst wrote: Interestingly in mathematics associative means that it doesn't matter whether you use (a.b).c or a.(b.c). Using xxx-associativity to indicate that it *does* matter is a bit perverse, but the Perl people are not to blame if they use a term in their usual sense. You may see it this way: Def1. An operator +:SxS->S is left-associative iff a+b+c = (a+b)+c for all a,b,c in S. Def2. An operator +:SxS->S is right-associative iff a+b+c = a+(b+c) for all a,b,c in S. Def3. An operator +:SxS->S is associative iff it is both left and right-associative. I know, but what the mathematicians do make so much more sense: (a+b)+c = a+(b+c)definition of associative. Henceforth we may leave out the brackets. That's Def3. I don't see your point. Don't leave out the brackets if the operators if the operators is not associative. (1 - 1) - 1 != 1 - (1 - 1) and yet we can leave out the parentheses. P.S. There is no need for the operators to be SxS->S. For example a b c may be m by n, n by l, l by k matrices respectively. Ops, you're right. Kiuhnm -- http://mail.python.org/mailman/listinfo/python-list
Re: New Science Discovery: Perl Idiots Remain Idiots After A Decade!New Science Discovery: Perl Idiots Remain Idiots After A Decade!
On 3/12/2012 20:00, Albert van der Horst wrote: In article<4f5df4b3$0$1375$4fafb...@reader1.news.tin.it>, Kiuhnm wrote: On 3/12/2012 12:27, Albert van der Horst wrote: Interestingly in mathematics associative means that it doesn't matter whether you use (a.b).c or a.(b.c). Using xxx-associativity to indicate that it *does* matter is a bit perverse, but the Perl people are not to blame if they use a term in their usual sense. You may see it this way: Def1. An operator +:SxS->S is left-associative iff a+b+c = (a+b)+c for all a,b,c in S. Def2. An operator +:SxS->S is right-associative iff a+b+c = a+(b+c) for all a,b,c in S. Def3. An operator +:SxS->S is associative iff it is both left and right-associative. I know, but what the mathematicians do make so much more sense: (a+b)+c = a+(b+c)definition of associative. Henceforth we may leave out the brackets. That's Def3. I don't see your point. Don't leave out the brackets if the operators if the operators is not associative. (1 - 1) - 1 != 1 - (1 - 1) and yet we can leave out the parentheses. P.S. There is no need for the operators to be SxS->S. For example a b c may be m by n, n by l, l by k matrices respectively. Ops, you're right. Kiuhnm -- http://mail.python.org/mailman/listinfo/python-list
Re: New Science Discovery: Perl Idiots Remain Idiots After A Decade!New Science Discovery: Perl Idiots Remain Idiots After A Decade!
On 3/12/2012 20:00, Albert van der Horst wrote: In article<4f5df4b3$0$1375$4fafb...@reader1.news.tin.it>, Kiuhnm wrote: On 3/12/2012 12:27, Albert van der Horst wrote: Interestingly in mathematics associative means that it doesn't matter whether you use (a.b).c or a.(b.c). Using xxx-associativity to indicate that it *does* matter is a bit perverse, but the Perl people are not to blame if they use a term in their usual sense. You may see it this way: Def1. An operator +:SxS->S is left-associative iff a+b+c = (a+b)+c for all a,b,c in S. Def2. An operator +:SxS->S is right-associative iff a+b+c = a+(b+c) for all a,b,c in S. Def3. An operator +:SxS->S is associative iff it is both left and right-associative. I know, but what the mathematicians do make so much more sense: (a+b)+c = a+(b+c)definition of associative. Henceforth we may leave out the brackets. That's Def3. I don't see your point. Don't leave out the brackets if the operators if the operators is not associative. (1 - 1) - 1 != 1 - (1 - 1) and yet we can leave out the parentheses. P.S. There is no need for the operators to be SxS->S. For example a b c may be m by n, n by l, l by k matrices respectively. Ops, you're right. Kiuhnm -- http://mail.python.org/mailman/listinfo/python-list
Re: New Science Discovery: Perl Idiots Remain Idiots After A Decade!New Science Discovery: Perl Idiots Remain Idiots After A Decade!
In article <4f5df4b3$0$1375$4fafb...@reader1.news.tin.it>, Kiuhnm wrote: >On 3/12/2012 12:27, Albert van der Horst wrote: >> Interestingly in mathematics associative means that it doesn't matter >> whether you use (a.b).c or a.(b.c). >> Using xxx-associativity to indicate that it *does* matter is >> a bit perverse, but the Perl people are not to blame if they use >> a term in their usual sense. > >You may see it this way: >Def1. An operator +:SxS->S is left-associative iff > a+b+c = (a+b)+c for all a,b,c in S. >Def2. An operator +:SxS->S is right-associative iff > a+b+c = a+(b+c) for all a,b,c in S. >Def3. An operator +:SxS->S is associative iff it is both left and >right-associative. I know, but what the mathematicians do make so much more sense: (a+b)+c = a+(b+c)definition of associative. Henceforth we may leave out the brackets. Don't leave out the brackets if the operators if the operators is not associative. P.S. There is no need for the operators to be SxS->S. For example a b c may be m by n, n by l, l by k matrices respectively. > >Kiuhnm Groetjes Albert -- -- Albert van der Horst, UTRECHT,THE NETHERLANDS Economic growth -- being exponential -- ultimately falters. albert@spe&ar&c.xs4all.nl &=n http://home.hccnet.nl/a.w.m.van.der.horst -- http://mail.python.org/mailman/listinfo/python-list
Re: New Science Discovery: Perl Idiots Remain Idiots After A Decade!New Science Discovery: Perl Idiots Remain Idiots After A Decade!
On 3/12/2012 12:27, Albert van der Horst wrote: Interestingly in mathematics associative means that it doesn't matter whether you use (a.b).c or a.(b.c). Using xxx-associativity to indicate that it *does* matter is a bit perverse, but the Perl people are not to blame if they use a term in their usual sense. You may see it this way: Def1. An operator +:SxS->S is left-associative iff a+b+c = (a+b)+c for all a,b,c in S. Def2. An operator +:SxS->S is right-associative iff a+b+c = a+(b+c) for all a,b,c in S. Def3. An operator +:SxS->S is associative iff it is both left and right-associative. Kiuhnm -- http://mail.python.org/mailman/listinfo/python-list
Re: New Science Discovery: Perl Idiots Remain Idiots After A Decade!New Science Discovery: Perl Idiots Remain Idiots After A Decade!
In article <0078bbfb-5dfc-48fc-af1a-69de3cf15...@b1g2000yqb.googlegroups.com>, Xah Lee wrote: >New Science Discovery: Perl Idiots Remain Idiots After A Decade! > >A excerpt from the new book =E3=80=88Modern Perl=E3=80=89, just published, = >chapter 4 >on =E2=80=9COperators=E2=80=9D. Quote: > >=C2=ABThe associativity of an operator governs whether it evaluates from >left to right or right to left. Addition is left associative, such >that 2 + 3 + 4 evaluates 2 + 3 first, then adds 4 to the result. >Exponentiation is right associative, such that 2 ** 3 ** 4 evaluates 3 >** 4 first, then raises 2 to the 81st power. =C2=BB > >LOL. Looks like the perl folks haven't changed. Fundamentals of >serious math got botched so badly. You're confused. Associativity of operators is defined in mathematics. (The same concept may be used in programming). "left-associativity" and "right-associativity" are computer languages concept and their definitions are not from mathematics. Interestingly in mathematics associative means that it doesn't matter whether you use (a.b).c or a.(b.c). Using xxx-associativity to indicate that it *does* matter is a bit perverse, but the Perl people are not to blame if they use a term in their usual sense. Groetjes Albert -- -- Albert van der Horst, UTRECHT,THE NETHERLANDS Economic growth -- being exponential -- ultimately falters. albert@spe&ar&c.xs4all.nl &=n http://home.hccnet.nl/a.w.m.van.der.horst -- http://mail.python.org/mailman/listinfo/python-list
Re: New Science Discovery: Perl Idiots Remain Idiots After A Decade!New Science Discovery: Perl Idiots Remain Idiots After A Decade!
On 3/2/2012 14:12, Xah Lee wrote: On Mar 1, 3:00 am, Kiuhnm wrote: They did not make up the terminology, if that is what you are saying. The concepts of left and right associativity are well-known and accepted in TCS (Theoretical CS). Aho, Sethi and Ullman explain it this way in "Compilers: Principles, Techniques and Tools": "We say that the operator + associates to the left because an operand with plus signs on both sides of it is taken by the operator to its left. [...]" And they also show parse trees similar to the ones I wrote above. how do they explain when 2 operators are adjacent e.g. 「3 △ 6 ▲ 5 」? The same way you do, I guess. An operand that has operators on both sides is operand of the operator of higher precedence. For instance, in 3 * 4 + 6 4 is operand of * but not of +. Indeed, the operands of + are 3*4 and 6. do you happen to know some site that shows the relevant page i can have a look? Nope, sorry. Kiuhnm -- http://mail.python.org/mailman/listinfo/python-list
Re: New Science Discovery: Perl Idiots Remain Idiots After A Decade!New Science Discovery: Perl Idiots Remain Idiots After A Decade!
On Mar 1, 3:00 am, Kiuhnm wrote: > They did not make up the terminology, if that is what you are saying. > The concepts of left and right associativity are well-known and accepted > in TCS (Theoretical CS). > Aho, Sethi and Ullman explain it this way in "Compilers: Principles, > Techniques and Tools": > "We say that the operator + associates to the left because an operand > with plus signs on both sides of it is taken by the operator to its > left. [...]" > And they also show parse trees similar to the ones I wrote above. how do they explain when 2 operators are adjacent e.g. 「3 △ 6 ▲ 5 」? do you happen to know some site that shows the relevant page i can have a look? thanks. Xah On Mar 1, 3:00 am, Kiuhnm wrote: > On 3/1/2012 1:02, Xah Lee wrote: > > > i missed a point in my original post. That is, when the same operator > > are adjacent. e.g. 「3 ▲ 6 ▲ 5」. > > > This is pointed out by Kiuhnm 〔kiuhnm03.4t.yahoo.it〕 and Tim Bradshaw. > > Thanks. > > > though, i disagree the way they expressed it, or any sense this is > > different from math. > > They did not make up the terminology, if that is what you are saying. > The concepts of left and right associativity are well-known and accepted > in TCS (Theoretical CS). > > If you change the terminology, no one will understand you unless you > provide your definitions every time (and then they may not accept them). > > Another way of saying that an operator is left-associative is that its > parse tree is a left-tree, i.e. a complete tree where each right child > is a leaf. > For instance, (use a monospaced font) > 1 + 2 + 3 + 4 > gives you this left-tree: > + > + 4 > + 3 > 1 2 > while 1**2**3**4 > gives you this right-tree: > ** > 1 ** > 2 ** > 3 4 > > Aho, Sethi and Ullman explain it this way in "Compilers: Principles, > Techniques and Tools": > "We say that the operator + associates to the left because an operand > with plus signs on both sides of it is taken by the operator to its > left. [...]" > And they also show parse trees similar to the ones I wrote above. > > Kiuhnm -- http://mail.python.org/mailman/listinfo/python-list
Re: New Science Discovery: Perl Idiots Remain Idiots After A Decade!New Science Discovery: Perl Idiots Remain Idiots After A Decade!
On Wed, 29 Feb 2012 00:09:16 -0800, Xah Lee wrote: Xah, you won't grow even an inch taller by cutting others down. -- I joined scientology at a garage sale!! -- http://mail.python.org/mailman/listinfo/python-list
Re: New Science Discovery: Perl Idiots Remain Idiots After A Decade!New Science Discovery: Perl Idiots Remain Idiots After A Decade!
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
Re: New Science Discovery: Perl Idiots Remain Idiots After A Decade!New Science Discovery: Perl Idiots Remain Idiots After A Decade!
On 3/1/2012 1:02, Xah Lee wrote: i missed a point in my original post. That is, when the same operator are adjacent. e.g. 「3 ▲ 6 ▲ 5」. This is pointed out by Kiuhnm 〔kiuhnm03.4t.yahoo.it〕 and Tim Bradshaw. Thanks. though, i disagree the way they expressed it, or any sense this is different from math. They did not make up the terminology, if that is what you are saying. The concepts of left and right associativity are well-known and accepted in TCS (Theoretical CS). If you change the terminology, no one will understand you unless you provide your definitions every time (and then they may not accept them). Another way of saying that an operator is left-associative is that its parse tree is a left-tree, i.e. a complete tree where each right child is a leaf. For instance, (use a monospaced font) 1 + 2 + 3 + 4 gives you this left-tree: + + 4 + 3 1 2 while 1**2**3**4 gives you this right-tree: ** 1** 2** 3 4 Aho, Sethi and Ullman explain it this way in "Compilers: Principles, Techniques and Tools": "We say that the operator + associates to the left because an operand with plus signs on both sides of it is taken by the operator to its left. [...]" And they also show parse trees similar to the ones I wrote above. Kiuhnm -- http://mail.python.org/mailman/listinfo/python-list
Re: New Science Discovery: Perl Idiots Remain Idiots After A Decade!New Science Discovery: Perl Idiots Remain Idiots After A Decade!
i missed a point in my original post. That is, when the same operator are adjacent. e.g. 「3 ▲ 6 ▲ 5」. This is pointed out by Kiuhnm 〔kiuhnm03.4t.yahoo.it〕 and Tim Bradshaw. Thanks. though, i disagree the way they expressed it, or any sense this is different from math. to clarify, amend my original post, here's what's needed for binary operator precedence: ① the symbols are ordered. (e.g. given a unique integer) ② each symbol is has either one of left-side stickness or right-side stickness spec. (needed when adjacent symbols are the same.) About the lisp case mentioned by Tim, e.g. in「(f a b c)」, whether it means 「(f (f a b) c)」 or 「(f a (f b c))」 . It is not directly relevant to the context of my original post, because it isn't about to operators. It's about function argument eval order. Good point, nevertheless. the perl doc, is still misleading, terribly bad written. Becha ass! Xah On Feb 29, 4:08 am, Kiuhnm wrote: > On 2/29/2012 9:09, Xah Lee wrote: > > > > New Science Discovery: Perl Idiots Remain Idiots After A Decade! > > > A excerpt from the new book 〈Modern Perl〉, just published, chapter 4 > > on “Operators”. Quote: > > > «The associativity of an operator governs whether it evaluates from > > left to right or right to left. Addition is left associative, such > > that 2 + 3 + 4 evaluates 2 + 3 first, then adds 4 to the result. > > Exponentiation is right associative, such that 2 ** 3 ** 4 evaluates 3 > > ** 4 first, then raises 2 to the 81st power. » > > > LOL. Looks like the perl folks haven't changed. Fundamentals of > > serious math got botched so badly. > > > Let me explain the idiocy. > > > It says “The associativity of an operator governs whether it evaluates > > from left to right or right to left.”. Ok, so let's say we have 2 > > operators: a white triangle △ and a black triangle ▲. Now, by the > > perl's teaching above, let's suppose the white triangle is “right > > associative” and the black triangle is “left associative”. Now, look > > at this: > > > 3 △ 6 ▲ 5 > > > seems like the white and black triangles are going to draw a pistol > > and fight for the chick 6 there. LOL. > > Sorry, but you're wrong and they're right. > Associativity governs the order of evaluation of a group of operators > *OF THE SAME PRECEDENCE*. > If you write > 2**3**4 > only the fact the '**' is right associative will tell you that the order is > 2**(3**4) > and not > (2**3)**4 > I remind you that 2^(3^4) != (2^3)^4. > > Kiuhnm -- http://mail.python.org/mailman/listinfo/python-list
Re: New Science Discovery: Perl Idiots Remain Idiots After A Decade!New Science Discovery: Perl Idiots Remain Idiots After A Decade!
On Feb 29, 5:09 am, Xah Lee wrote: > New Science Discovery: Perl Idiots Remain Idiots After A Decade! > > A excerpt from the new book 〈Modern Perl〉, just published, chapter 4 > on “Operators”. Quote: > > «The associativity of an operator governs whether it evaluates from > left to right or right to left. Addition is left associative, such > that 2 + 3 + 4 evaluates 2 + 3 first, then adds 4 to the result. > Exponentiation is right associative, such that 2 ** 3 ** 4 evaluates 3 > ** 4 first, then raises 2 to the 81st power. » > > LOL. Looks like the perl folks haven't changed. Fundamentals of > serious math got botched so badly. > > Let me explain the idiocy. > > It says “The associativity of an operator governs whether it evaluates > from left to right or right to left.”. Ok, so let's say we have 2 > operators: a white triangle △ and a black triangle ▲. Now, by the > perl's teaching above, let's suppose the white triangle is “right > associative” and the black triangle is “left associative”. Now, look > at this: > > 3 △ 6 ▲ 5 > > seems like the white and black triangles are going to draw a pistol > and fight for the chick 6 there. LOL. > > 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. > > 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)」.) > > compare it with this: > > 〈Perl ＆ Python: Complex > Numbers〉http://xahlee.org/perl-python/complex_numbers.html > > and for a good understanding of functions and operators, see: > > 〈What's Function, What's > Operator?〉http://xahlee.org/math/function_and_operators.html associativity of operators mean little in the Lisp world obviously, so why was this posted here? Sorry, perl, python and emacs folks... BTW, it's the same in javascript: it is so such that 2 + 3 + "4" is "54" and "2" + 3 + 4 is "234". Blame weak typing and + overloading, though it may be a blessing. -- http://mail.python.org/mailman/listinfo/python-list
Re: New Science Discovery: Perl Idiots Remain Idiots After A Decade!New Science Discovery: Perl Idiots Remain Idiots After A Decade!
On 2/29/2012 16:15, Rainer Weikusat wrote: [...] 'mathematics' (an essentially outdated write-only programming language dating back to the times when humans had to perform computations themselves) [...] Theoretical Computer Science is a branch of mathematics. Are you saying it is outdated? Kiuhnm -- http://mail.python.org/mailman/listinfo/python-list
Re: New Science Discovery: Perl Idiots Remain Idiots After A Decade!New Science Discovery: Perl Idiots Remain Idiots After A Decade!
Xah Lee writes: > A excerpt from the new book 〈Modern Perl〉, just published, chapter 4 > on “Operators”. Quote: > > «The associativity of an operator governs whether it evaluates from > left to right or right to left. Addition is left associative, such > that 2 + 3 + 4 evaluates 2 + 3 first, then adds 4 to the result. > Exponentiation is right associative, such that 2 ** 3 ** 4 evaluates 3 > ** 4 first, then raises 2 to the 81st power. » > > LOL. Looks like the perl folks haven't changed. Fundamentals of > serious math got botched so badly. > > Let me explain the idiocy. > > It says “The associativity of an operator governs whether it evaluates > from left to right or right to left.”. Ok, so let's say we have 2 > operators: a white triangle △ and a black triangle ▲. Now, by the > perl's teaching above, let's suppose the white triangle is “right > associative” and the black triangle is “left associative”. Now, look > at this: > > 3 △ 6 ▲ 5 > > seems like the white and black triangles are going to draw a pistol > and fight for the chick 6 there. LOL. As the perlop manpage would have told you, Operator associativity defines what happens if a sequence of the same operators is used one after another Since this is not the case in your example, it doesn't seem to be applicable here. Also, the Perl I'm aware doesn't have 'white triangle' and 'black triangle' operators and it also doesn't have operators of equal precedence and different associativity. It can't, actually, since there would be no way to evaluate an expression like the mock one you invented above. Lastly, that something happens to be in one way or another way in the completely arbitrary set of rules and conventions commonly referred to as 'mathematics' (an essentially outdated write-only programming language dating back to the times when humans had to perform computations themselves) doesn't mean it is of any relevance anywhere else just because of this, no matter how dear it might be to lots of people. -- http://mail.python.org/mailman/listinfo/python-list
Re: New Science Discovery: Perl Idiots Remain Idiots After A Decade!New Science Discovery: Perl Idiots Remain Idiots After A Decade!
On Wed, Feb 29, 2012 at 6:43 AM, Chiron wrote: > Personally, I think this whole issue of precedence in a programming > language is over-rated. It seems to me that grouping of any non-trivial > set of calculations should be done so as to remove any possible confusion > as to intent. Some languages do this. e.g. all lisps. -- Devin -- http://mail.python.org/mailman/listinfo/python-list
Re: New Science Discovery: Perl Idiots Remain Idiots After A Decade!New Science Discovery: Perl Idiots Remain Idiots After A Decade!
On 2/29/2012 9:09, Xah Lee wrote: New Science Discovery: Perl Idiots Remain Idiots After A Decade! A excerpt from the new book 〈Modern Perl〉, just published, chapter 4 on “Operators”. Quote: «The associativity of an operator governs whether it evaluates from left to right or right to left. Addition is left associative, such that 2 + 3 + 4 evaluates 2 + 3 first, then adds 4 to the result. Exponentiation is right associative, such that 2 ** 3 ** 4 evaluates 3 ** 4 first, then raises 2 to the 81st power. » LOL. Looks like the perl folks haven't changed. Fundamentals of serious math got botched so badly. Let me explain the idiocy. It says “The associativity of an operator governs whether it evaluates from left to right or right to left.”. Ok, so let's say we have 2 operators: a white triangle △ and a black triangle ▲. Now, by the perl's teaching above, let's suppose the white triangle is “right associative” and the black triangle is “left associative”. Now, look at this: 3 △ 6 ▲ 5 seems like the white and black triangles are going to draw a pistol and fight for the chick 6 there. LOL. Sorry, but you're wrong and they're right. Associativity governs the order of evaluation of a group of operators *OF THE SAME PRECEDENCE*. If you write 2**3**4 only the fact the '**' is right associative will tell you that the order is 2**(3**4) and not (2**3)**4 I remind you that 2^(3^4) != (2^3)^4. Kiuhnm -- http://mail.python.org/mailman/listinfo/python-list
Re: New Science Discovery: Perl Idiots Remain Idiots After A Decade!New Science Discovery: Perl Idiots Remain Idiots After A Decade!
On Wed, 29 Feb 2012 00:09:16 -0800, Xah Lee wrote: Personally, I think this whole issue of precedence in a programming language is over-rated. It seems to me that grouping of any non-trivial set of calculations should be done so as to remove any possible confusion as to intent. It is one more obstacle to accidental errors in logic, where you intend one thing, possibly overlook precedence, and get a strange result. Sure, mathematically it *should* go a particular way, and any programming language *should* follow that. Still... they don't, and since they don't it makes more sense to be really obvious what you meant to do. As someone pointed out, a programming language is for humans; computers don't need them. That being the case, it makes sense to keep things as clear as possible. -- It's OKAY -- I'm an INTELLECTUAL, too. -- http://mail.python.org/mailman/listinfo/python-list
New Science Discovery: Perl Idiots Remain Idiots After A Decade!New Science Discovery: Perl Idiots Remain Idiots After A Decade!
New Science Discovery: Perl Idiots Remain Idiots After A Decade! A excerpt from the new book 〈Modern Perl〉, just published, chapter 4 on “Operators”. Quote: «The associativity of an operator governs whether it evaluates from left to right or right to left. Addition is left associative, such that 2 + 3 + 4 evaluates 2 + 3 first, then adds 4 to the result. Exponentiation is right associative, such that 2 ** 3 ** 4 evaluates 3 ** 4 first, then raises 2 to the 81st power. » LOL. Looks like the perl folks haven't changed. Fundamentals of serious math got botched so badly. Let me explain the idiocy. It says “The associativity of an operator governs whether it evaluates from left to right or right to left.”. Ok, so let's say we have 2 operators: a white triangle △ and a black triangle ▲. Now, by the perl's teaching above, let's suppose the white triangle is “right associative” and the black triangle is “left associative”. Now, look at this: 3 △ 6 ▲ 5 seems like the white and black triangles are going to draw a pistol and fight for the chick 6 there. LOL. 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. 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)」.) compare it with this: 〈Perl ＆ Python: Complex Numbers〉 http://xahlee.org/perl-python/complex_numbers.html and for a good understanding of functions and operators, see: 〈What's Function, What's Operator?〉 http://xahlee.org/math/function_and_operators.html -- http://mail.python.org/mailman/listinfo/python-list
