Arithmetic expression and TRY_BLOCK_ERROR

Arithmetic expression and TRY_BLOCK_ERROR

[DervishD]

    Hi all :)

    I'll try to make it short ;) Why this:

    ...
    (( TRY_BLOCK_ERROR = 0 ))
    ...

    and not just this:

    ...
    TRY_BLOCK_ERROR=0
    ...
    ?????

    Thanks a lot :) If anyone is interested, take a look at zsh-users
8485 and 8489.
    
    Raúl Núñez de Arenas Coronado

-- 
Linux Registered User 88736 | http://www.dervishd.net
http://www.pleyades.net & http://www.gotesdelluna.net
It's my PC and I'll cry if I want to...

Re: Arithmetic expression and TRY_BLOCK_ERROR

[John Reese]

2005/9/27, DervishD <zsh@dervishd.net>:
>     Hi all :)
>     I'll try to make it short ;) Why this:
>     ...
>     (( TRY_BLOCK_ERROR = 0 ))
>     ...
>     and not just this:
>     ...
>     TRY_BLOCK_ERROR=0
>     ...
>     ?????
>

The parentheses make it an integer variable.  Also, that particular
assignment sets $? to 1.  Maybe that's desired.  I don't know. 
Probably it's just that it's a fairly compact syntax for setting an
integer variable.

ofb:1% thok=0                                                       17:08 ofb:~
ofb:1% (( khot = 0 ))                                               17:08 ofb:~
ofb:1% integer xox=0                                            17:08 <1> ofb:~
ofb:1% let box=0                                                    17:08 ofb:~
ofb:1% typeset -p thok khot xox box                                 17:09 ofb:~
typeset thok=0
typeset -i khot=0
typeset -i xox=0
typeset -i box=0

Re: Arithmetic expression and TRY_BLOCK_ERROR

[Will Maier]

On Tue, Sep 27, 2005 at 05:11:28PM -0700, John Reese wrote:
[snip]
> ofb:1% thok=0                                                       17:08 ofb:~

Would you mind sharing the code in you .zshrc that generates that
attractive, spartan prompt?

-- 

[Will Maier]---------------[willmaier@ml1.net/wcmaier@jabber.ccc.de]

Re: Arithmetic expression and TRY_BLOCK_ERROR

[John Reese]

2005/9/27, Will Maier <willmaier@ml1.net>:
> On Tue, Sep 27, 2005 at 05:11:28PM -0700, John Reese wrote:
> [snip]
> > ofb:1% thok=0                                                       17:08 ofb:~
>
> Would you mind sharing the code in you .zshrc that generates that
> attractive, spartan prompt?
>

RPS1='%B%T %(0?,,<%?> )%m:%~%b'
PS1="%Bofb${WINDOW:+:$WINDOW}%#%b"

The right prompt displays the status code of the last command if it
was non-zero, and if I'm running inside screen the screen number goes
in the left prompt.

Re: Arithmetic expression and TRY_BLOCK_ERROR

[DervishD]

    Hi John :)

 * John Reese <john.reese@gmail.com> dixit:
> 2005/9/27, DervishD <zsh@dervishd.net>:
> >     Hi all :)
> >     I'll try to make it short ;) Why this:
> >     ...
> >     (( TRY_BLOCK_ERROR = 0 ))
> >     ...
> >     and not just this:
> >     ...
> >     TRY_BLOCK_ERROR=0
> >     ...
> >     ?????
> >
> The parentheses make it an integer variable.

    I know it, what I don't understand is why is it needed :? I mean,
that variable is already an integer variable.

>  Also, that particular
> assignment sets $? to 1.  Maybe that's desired.  I don't know. 

    Not in that context (is the code of the "throw" and "catch"
functions).

> Probably it's just that it's a fairly compact syntax for setting an
> integer variable.

    'let variable=0' is shorter ;) I really don't know the reason,
but I can find this kind of assignment everywhere :-/

    Raúl Núñez de Arenas Coronado

-- 
Linux Registered User 88736 | http://www.dervishd.net
http://www.pleyades.net & http://www.gotesdelluna.net
It's my PC and I'll cry if I want to...

Re: Arithmetic expression and TRY_BLOCK_ERROR

[Bart Schaefer]

On Sep 28, 10:46am, DervishD wrote:
}
}     'let variable=0' is shorter ;) I really don't know the reason,
} but I can find this kind of assignment everywhere :-/

I suspect it's simply Peter's preference to always use variables in
a consistent context, i.e., either in math expressions or out, not
some of each.  A possible reason for this is future-proofing.
Suppose you have:

	(( variable = 0 ))	# or any other integer constant

Then later that gets changed to:

	(( variable = othervariable ))

If you had instead written it without the (( )), the meaning of:

	variable=othervariable

is entirely different.

Also, some people prefer the readability of being able to put spaces
around the "=".

However, doing integer/float assignments in math context is marginally
more efficient than doing them as plain assignments.  In a single
command this is probably offset by the overhead of parsing the (( )),
but in a loop it could become important, and if you're in the habit of
always writing the (( )) you won't forget them where they matter.

Re: Arithmetic expression and TRY_BLOCK_ERROR

[DervishD]

    Hi Bart :)

 * Bart Schaefer <schaefer@brasslantern.com> dixit:
> On Sep 28, 10:46am, DervishD wrote:
> }
> }     'let variable=0' is shorter ;) I really don't know the reason,
> } but I can find this kind of assignment everywhere :-/
> I suspect it's simply Peter's preference to always use variables in
> a consistent context, i.e., either in math expressions or out, not
> some of each.  A possible reason for this is future-proofing.

    I understand, thanks for the explanation :)

> Also, some people prefer the readability of being able to put spaces
> around the "=".

    Me, for example. In fact, the entire ((...)) syntax is quite good
when reading shource files, it really catches the eye.
 
> However, doing integer/float assignments in math context is marginally
> more efficient than doing them as plain assignments.  In a single
> command this is probably offset by the overhead of parsing the (( )),
> but in a loop it could become important, and if you're in the habit of
> always writing the (( )) you won't forget them where they matter.

    Thanks for both the explanation and the advice :)

    Raúl Núñez de Arenas Coronado

-- 
Linux Registered User 88736 | http://www.dervishd.net
http://www.pleyades.net & http://www.gotesdelluna.net
It's my PC and I'll cry if I want to...