Yeah, you reminded me of something...
Most 'common problems' with tcl/tk are the "lists theory", substitution theory,
and command theory.
In short, the 'lists theory' is that everything is a list, and tcl works a lot
with list manipulations.
substitution theory is that, if I do "function $arg" the $arg will be
substituted, and if it had a space, the
'function' will get two arguments, if I do {function $arg} (the {} means it's a
list) the $arg will not be
substituted and the argument will be the same as if I wrote "function \$arg".
If I do [list function $arg] then
$arg will be substituted but if it had a space in it, it will still count as
one argument (not two like
before).. actually $arg will become a list element.
Example :
set file "c:\My documents\file.txt"
if you do
button .b -command "open $file"
then it will fail because it would be the same as doing :
button .b -command "open c:\My documents\file.txt"
(this is what will be stored), so once evaluated, it will evaluate "C:\My" as
the first argument and
"documents\file.txt" as the second argument.
If you do :
button .b -command {open $file}
then it will fail because it will say "$file : file not found" unless you
create a file named "$file"
if you do :
button .b -command [list open $file]
then it will work because Tcl will store the callback as : {open {C:\My
documents\file.txt}} (a list with two
elements, the first being the command, the second being the argument).
and finally, about the 'command theory', it's to say that EVERYTHING is a
command. even 'if'.. so the if is a
command which takes :
if expression body ?elseif body? ?elseif body? ... ?else body?
so if you do :
if $a return
it works, if you want to do :
if $a == $b return
it won't work because you sent "$a" as one argument "==" as a second argument
(the body '==' is invalid, it
would say that '==' is not a valid command) and $b as the third argument (again
error because it only accepts
else and elseif) and return as the 4th argument. So you group them into a list :
if {$a == $b} return
the {$a == $b} becomes a list. You could have also done :
if [list $a == $b] return
but it's better to put braces, and the 'if' command will evaluate the
expression and *substitute in the parent
namespace* (which is why it works, even if { } will disable substitution).
Also, you CAN'T do :
if {$a == $b} {
return 0
}
else
{
return 1
}
because it will say "else : invalid command". The commands are delimited by
either a ';' or by a newline, so
when you close the brace after the if and go to the next line, it means that
you finished with the 'if'. This
means you HAVE to put the 'else' on the same line as the closing brace of the
body, like this :
if {$a == $b} {
return 0
} else {
return 1
}
The same applies for the 'else' you can't put a newline after the 'else',
otherwise it will say "{ : invalid
command".
You can put newlines inside the body of the if only because we do a { } (if you
do [list] you'll need to put a
backslash at the end of each line otherwise it will say "missing close
bracket", like this :
if {$a == $b} [list \
return 0 \
] else [list \
return 1
]
but you DON'T WANT TO DO THIS because... well, remember { } allows you to
disable substitution, so if you do for
example :
if {$a == $b} [list return [exit]]
then when evaluation the 'if', the [list return [exit]] will be evaluated (to
go as an argument of the if) and
'exit' will be called even if $a != $b.
So to continue, when you do the { }, nothing is evaluated, so if you do
if { $a == $b } {
return 0
}
then if will get 2 arguments, the first being the expression and the second
being a list containing multiple
elements : a newline, a series of spaces, a 'return', a '0' and a newline. When
the 'if' will evaluated that
list, it will be evaluated as code and the variables/commands will be
substituted/evaluated and the newlines
will be interpreted as command delimiters.
You can also do something like this :
set body { whatever_function $arg
return 0
}
if {$a == $b} $body
and since $body is not between { } it will be replaced by the code above...
beware, if you did :
if {$a == $b} {$body }
then $body will only be substituted AFTER the if is entered and will be
evaluated as one command, it will say
that :
{whatever_function $arg
return 0
} : invalid command
oh and yes, if you were meant to ask, yes, you can put newlines and put spaces
in a command, so if you do :
proc {a
b
c} { } {puts 'abc called'}
a command called {a
b
c} will be created. And you can call it with
{a
b
c}
or with :
set command "a\nb\nc"
$command
it's fun Tcl, right ? you just need to understand those three basics, anything
is a command getting executed..
the tcl keywords are just 'built-in' commands (like if), understand lists and
substitutions... and once you get
that, you can do a lot of fancy stuff (like commands with spaces or newlines in
them :p)
Finally, here are three interesting links in the forums in which I explained
what I just explained in this mail,
a bit differently, maybe better, with other examples, and probably with a bit
more info. So please read them
too.
http://www.amsn-project.net/forums/viewtopic.php?p=17467
http://www.amsn-project.net/forums/viewtopic.php?p=5801#5801
http://www.amsn-project.net/forums/viewtopic.php?p=4461#4461
and I would REALLY love it if someone could summarize all this (or just
copy/paste it?) to the wiki in a page
like Dev:Tcl/Tk_Tutorials
p.s.: I never tried/tested the commands with newlines, but I'm guessing they
will work,I know that if I had put
$body, it will tell me an error trying to execute a command containing the
newline, but I never created one in
itself.
Thanks and have fun!
KaKaRoTo
On Thu, May 31, 2007 at 12:05:49AM +0200, Mirko Hansen wrote:
> Wow thanks a lot everybody for this nice welcome. It's a real pleasure to
> me. I think I should introduce myself roughly. Well, I think you all already
> know, but my name is Mirko. ;) I'm 24 years old, living in Germany, and
> actually I'm studying computer science at university. It's sometimes really
> time-consuming, especially if we have those really nice homeworks like the
> last two days, but I hope I'll be of use for the team, anyway I'll give my
> best to. As Youness said, I'm very new to TCL, I never had to deal with it
> before, so I would be really grateful if you advise me of my possibly made
> mistakes, to be able to learn from them. :)
>
> I think you'll hear from me soon. To a great teamwork! :)
>
> Bye,
> Mirko
>
> 2007/5/30, Youness Alaoui <[EMAIL PROTECTED]>:
> >
> >yeah, sounds intriguing right ?
> >well, baaazen is the username of Mirko. And this mail is to announce that
> >he's been added as part of the team.
> >So everyone, please welcome Mirko into the team, and please be helpful.
> >Mirko, if you need anything, don't hesitate to ask. I think you've been
> >following the ML for a little while now
> >so you should know how we work. in short ;
> >1 - a bugfix, you can commit
> >2 - a change to the UI should be discussed
> >3 - a change of behavior should be discussed
> >4 - a new feature should be discussed.
> >
> >Mirko is still studying and won't have much time (like everyone else) but
> >he promised to do his best to try and
> >help. He doesn't know much Tcl but from the patches he sent, it shows that
> >he's very skilled and I'm sure he'll
> >learn it all pretty soon.
> >
> >KaKaRoTo
> >
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