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New Science Discovery: Perl Idiots Remain Idiots After A Decade!New

 
 
Xah Lee
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      02-29-2012
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
 
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Chiron
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      02-29-2012
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.
 
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Rainer Weikusat
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      02-29-2012
Xah Lee <(E-Mail Removed)> 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.
 
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Chiron
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      02-29-2012
On Wed, 29 Feb 2012 17:18:24 +0100, Kiuhnm wrote:

> 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


Neither mathematics nor computer science is outdated. Such an assertion
is without merit.

Mathematics is not exclusively - nor even primarily - concerned with
computations.



--
Can anything be sadder than work left unfinished? Yes, work never begun.
 
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namekuseijin
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      02-29-2012
On Feb 29, 5:09*am, Xah Lee <(E-Mail Removed)> 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 ofoperators
> 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.
 
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Xah Lee
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      03-01-2012
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:

* 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 <kiuhnm03.4t.yahoo.it> 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 have2
> > 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

 
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Chiron
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      03-01-2012
On Wed, 29 Feb 2012 23:06:42 -0500, Shmuel (Seymour J.) Metz wrote:

> In <ubo3r.20367$(E-Mail Removed)>, on 02/29/2012
> at 11:43 AM, Chiron <(E-Mail Removed)> said:
>
>>Sure, mathematically it *should* go a particular way,

>
> No. Mathematically it should go the way that it is defined to go. There
> is nothing in Mathematics that either requires or prohibits infix
> notation in programming languages, or even in Mathematical notation.
>

Yes. That (the mathematically defined way) is a particular way, is it
not?

>>it makes sense to keep things as clear as possible.

>
> Often infix notation with well thought out precedence is the clearest
> way to go. RPN and the like have their place, but often are difficult
> for real people to read.


However, I wasn't specifically referring to infix/postfix/prefix or
anything of that nature. I wasn't limiting my comment to lisp notation
in particular, since what I said applies to any language. I was
referring to the placement of parentheses (or other groupings) to
indicate to *humans* what the intended sequence of events was. The
problem with precedence is that it is not always clear how it will go.
Different languages have different rules, some of which depart from the
rules in mathematics. Some implementations of languages are buggy in
this regard.

Mathematically, and in any language with which I am familiar, the
sequence: 2 + 6 / 3 will yield 4. It is unnecessary, but harmless, to
write this as 2 + (6 / 3). A naive reader (or just a tired or hurried
one) might come up with 8 / 3 if there aren't any parentheses.

Whenever there is *any* possibility of ambiguity, I see no reason not to
clarify. Back in the days when the way you wrote your code affected how
it was compiled, it made sense to rely heavily on language-specific
features, thus saving a few bytes. With gigabyte memories, gigahertz
clock speeds, and optimizing compilers, the pressure to try to optimize
by hand is gone. A few extra parentheses, or even breaking down a
complex sequence of events into discrete, simpler ones, is no longer a
costly luxury. A few extra variables, if they help clarity, aren't going
to hurt anything. Let the machine do the grunt work. Pamper your
readers (which in a few weeks or months might be you) and show exactly
what you had in mind. That's all I'm saying.

--
I'd just as soon kiss a Wookie.
-- Princess Leia Organa
 
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Chiron
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      03-01-2012
On Wed, 29 Feb 2012 23:10:48 -0500, Shmuel (Seymour J.) Metz wrote:

> ROTF,LMAO! You obviously don't have a clue as to what Mathematics means.
> Free hint: it doesn't mean Arithmetic. You're as bigoted as Xah Lee,



Hmm... maybe, instead of just ridiculing him, you could explain where he
is mistaken. Of course, doing that is a *LOT* harder than just calling
him a bigot.

BTW, I happen to agree with you insofar as this poster not understanding
the nature of mathematics. His comment reminds me of the article,
"Transgressing the Boundaries: Towards a Transformative Hermeneutics of
Quantum Gravity" (http://www.physics.nyu.edu/sokal/transgress_v2/
transgress_v2_singlefile.html). Also known as the "Sokal Hoax."

--
Boling's postulate:
If you're feeling good, don't worry. You'll get over it.
 
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Rainer Weikusat
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      03-01-2012
Shmuel (Seymour J.) Metz <(E-Mail Removed)> writes:
> In <(E-Mail Removed) >, on 02/29/2012
> at 03:15 PM, Rainer Weikusat <(E-Mail Removed)> said:
>
>>'mathematics' (an essentially outdated write-only programming
>>language dating back to the times when humans had to perform
>>computations themselves)

>
> ROTF,LMAO! You obviously don't have a clue as to what Mathematics
> means. Free hint: it doesn't mean Arithmetic.


You obviously don't have any sense of humour. But don't let this
trouble you.
 
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Chiron
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      03-02-2012
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!!
 
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