Avoiding local variable declarations?

[Marc 'BlackJack' Rintsch]

Re: Avoiding local variable declarations?

On Mon, 17 Nov 2008 10:10:16 +0000, Jorgen Grahn wrote:

On Thu, 13 Nov 2008 12:49:02 -0800 (PST), dpapathanasiou
<denis.papathan asiou@gmail.com wrote: ...

>>but what's wrong with you original code?

>>
>I come from a functional programming school of thought, where you avoid
>local variable declarations if at all possible.

>
I'm not sure that's universal. Using Standard ML at Uni, it was often
useful to use "let name = expr in expr" (or whatever the syntax was) to
simplify an expression. Directly borrowed from mathematics, I assume.

That's (also?) Haskell syntax and I agree that it is useful to write
readable code.

'name' is not a variable, of course; there are no variables in
functional programming. Can't remember what it's called -- named
expression, maybe?

I think it's called variable and works like variables work in
mathematics, i.e. you can assign only once. Not such illogical crap like
``a = a + 1`` which must be obviously false unless 1 is defined as the
neutral element for the definition of ``+`` here. :-)

Ciao,
Marc 'BlackJack' Rintsch

[Steven D'Aprano]

Re: Avoiding local variable declarations?

On Mon, 17 Nov 2008 12:32:35 +0000, Marc 'BlackJack' Rintsch wrote:

Not such illogical crap like
``a = a + 1`` which must be obviously false unless 1 is defined as the
neutral element for the definition of ``+`` here.

I don't quite know what you mean by "neutral element". I think you mean
the identity element under addition, which is zero, but that doesn't work:

0 = 0 + 1

Obviously not.

I think the only workable answer might be a = infinity, but that has two
problems: (1) infinity isn't a valid integer or real number (although
there is a valid float representing infinity on many platforms); and (2)
which infinity? Aleph 0, aleph 1, c, ... There's an infinite number of
them.



--
Steven

[Gabriel Genellina]

Re: Avoiding local variable declarations?

En Mon, 17 Nov 2008 22:18:51 -0200, Steven D'Aprano
<steven@remove. this.cybersourc e.com.auescribi ó:

On Mon, 17 Nov 2008 12:32:35 +0000, Marc 'BlackJack' Rintsch wrote:
>

>Not such illogical crap like
>``a = a + 1`` which must be obviously false unless 1 is defined as the
>neutral element for the definition of ``+`` here.

>
I don't quite know what you mean by "neutral element". I think you mean
the identity element under addition, which is zero, but that doesn't
work:
>
0 = 0 + 1
>
Obviously not.

Perhaps you didn't read carefully the above post? He said "unless *1* is
defined as the neutral element for ``+``"
Calling "1" the identity of the "+" operation, or calling "+" an operation
having "1" as its identity element is, errr, uncommon at least, but
perfectly valid...

--
Gabriel Genellina

[Russ P.]

Re: Avoiding local variable declarations?

On Nov 17, 5:12 pm, "Gabriel Genellina" <gagsl-...@yahoo.com.a r>
wrote:

En Mon, 17 Nov 2008 22:18:51 -0200, Steven D'Aprano
<ste...@remove. this.cybersourc e.com.auescribi ó:
>

On Mon, 17 Nov 2008 12:32:35 +0000, Marc 'BlackJack' Rintsch wrote:

>

Not such illogical crap like
``a = a + 1`` which must be obviously false unless 1 is defined as the
neutral element for the definition of ``+`` here.

>

I don't quite know what you mean by "neutral element". I think you mean
the identity element under addition, which is zero, but that doesn't
work:

>

0 = 0 + 1

>

Obviously not.

>
Perhaps you didn't read carefully the above post? He said "unless *1* is
defined as the neutral element for ``+``"
Calling "1" the identity of the "+" operation, or calling "+" an operation
having "1" as its identity element is, errr, uncommon at least, but
perfectly valid...
>
--
Gabriel Genellina

def __add__(self, other): return self + other - 1

Don't tell me this is not "Pythonic"!

[Steven D'Aprano]

Re: Avoiding local variable declarations?

On Mon, 17 Nov 2008 23:12:25 -0200, Gabriel Genellina wrote:

Perhaps you didn't read carefully the above post?

Er, yes, you got me on that.

:(


--
Steven

[Marc 'BlackJack' Rintsch]

Re: Avoiding local variable declarations?

On Tue, 18 Nov 2008 00:18:51 +0000, Steven D'Aprano wrote:

On Mon, 17 Nov 2008 12:32:35 +0000, Marc 'BlackJack' Rintsch wrote:
>

>Not such illogical crap like
>``a = a + 1`` which must be obviously false unless 1 is defined as the
>neutral element for the definition of ``+`` here.

>
I don't quite know what you mean by "neutral element". I think you mean
the identity element […]

I knew I should have looked it up instead of "translatin g" it from my
mother tongue -- yes I ment "identity element". Sorry for the confusion.

Ciao,
Marc 'BlackJack' Rintch

[Arnaud Delobelle]

Re: Avoiding local variable declarations?

Marc 'BlackJack' Rintsch <bj_666@gmx.net writes:

On Tue, 18 Nov 2008 00:18:51 +0000, Steven D'Aprano wrote:
>

>On Mon, 17 Nov 2008 12:32:35 +0000, Marc 'BlackJack' Rintsch wrote:
>>

>>Not such illogical crap like
>>``a = a + 1`` which must be obviously false unless 1 is defined as the
>>neutral element for the definition of ``+`` here.

>>
>I don't quite know what you mean by "neutral element". I think you mean
>the identity element […]

>
I knew I should have looked it up instead of "translatin g" it from my
mother tongue -- yes I ment "identity element". Sorry for the confusion.
>

Neutral element is correct. But maybe its use is limited to
mathematicians in the english-speaking word.

--
Arnaud

[Gabriel Genellina]

Re: Avoiding local variable declarations?

En Tue, 18 Nov 2008 16:27:46 -0200, Arnaud Delobelle
<arnodel@google mail.comescribi ó:

Marc 'BlackJack' Rintsch <bj_666@gmx.net writes:

>On Tue, 18 Nov 2008 00:18:51 +0000, Steven D'Aprano wrote:

>>On Mon, 17 Nov 2008 12:32:35 +0000, Marc 'BlackJack' Rintsch wrote:
>>>
>>>Not such illogical crap like
>>>``a = a + 1`` which must be obviously false unless 1 is defined as the
>>>neutral element for the definition of ``+`` here.
>>>
>>I don't quite know what you mean by "neutral element". I think you mean
>>the identity element […]

>I knew I should have looked it up instead of "translatin g" it from my
>mother tongue -- yes I ment "identity element". Sorry for the
>confusion.

Neutral element is correct. But maybe its use is limited to
mathematicians in the english-speaking word.

In Spanish I've seen "elemento neutro" and "elemento identidad" used
interchangeably .

--
Gabriel Genellina

[greg]

Re: Avoiding local variable declarations?

Arnaud Delobelle wrote:

Neutral element is correct. But maybe its use is limited to
mathematicians in the english-speaking word.

I've only ever seen "identity element" in English mathematics.
"Neutral element" sounds like something my car's gearbox
might have...

--
Greg

[Mark Wooding]

Re: Avoiding local variable declarations?

greg <greg@cosc.cant erbury.ac.nzwro te:

I've only ever seen "identity element" in English mathematics.
"Neutral element" sounds like something my car's gearbox
might have...

I've encountered both. I think `neutral element' is more common when
dealing with the possibility that it might not be unique (in the way
that identity elements are in groups, rings and fields), but that might
just be my misconception.

-- [mdw]

[Arnaud Delobelle]

Re: Avoiding local variable declarations?

greg <greg@cosc.cant erbury.ac.nzwri tes:

Arnaud Delobelle wrote:
>

>Neutral element is correct. But maybe its use is limited to
>mathematicia ns in the english-speaking word.

>
I've only ever seen "identity element" in English mathematics.
"Neutral element" sounds like something my car's gearbox
might have...

I was an academic mathematician for several years (although not a very
good one) and I can assure you that 'neutral element' is correct and
understood. 'Unit element' is another common synonym.

Unfortunately I can't find a reference in one of the few books in
English that I have at home. Lang's "Algebra" does not seem to use the
term and it's the only undergraduate book I've got. Wikipedia and other
internet sources cite 'neutral element' as a synonym to 'identity
element'.

--
Arnaud