Re: Test whether variable has been set

Re: Test whether variable has been set

[Elliot Clifton]

Hi Peter,

Thanks for your reply. I think I may have misunderstood the variable
section on the wiki. I been using \setvariable to both declare and
assign variables from my component files. When I should have been
declaring them in the environment file first, right?
\setvariable[namespace][key=DefaultValue], right? So how do I test for
a (Default)Value?
Sorry, I'm just beginning TeX programming I don't understand how to do this.

Elliot
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Re: Test whether variable has been set

[Aditya Mahajan]

On Sun, 27 May 2007, Elliot Clifton wrote:

> Hi Peter,
>
> Thanks for your reply. I think I may have misunderstood the variable
> section on the wiki. I been using \setvariable to both declare and
> assign variables from my component files. When I should have been
> declaring them in the environment file first, right?
> \setvariable[namespace][key=DefaultValue], right? So how do I test for
> a (Default)Value?
> Sorry, I'm just beginning TeX programming I don't understand how to do this.

Elliot,

You can use \doif{\getvalue{set}{var}}{value} for simple string 
comparisons. See http://wiki.contextgarden.net/System_Macros for basic 
flow control features of ConTeXt.

It may also be possble to see if variables have changed using setups 
http://wiki.contextgarden.net/Inside_ConTeXt#Using_setups_for_namespaces 
but I have never personally used that.

Aditya
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Re: Test whether variable has been set

[Hans Hagen]

Aditya Mahajan wrote:
> On Sun, 27 May 2007, Elliot Clifton wrote:
>
>   
>> Hi Peter,
>>
>> Thanks for your reply. I think I may have misunderstood the variable
>> section on the wiki. I been using \setvariable to both declare and
>> assign variables from my component files. When I should have been
>> declaring them in the environment file first, right?
>> \setvariable[namespace][key=DefaultValue], right? So how do I test for
>> a (Default)Value?
>> Sorry, I'm just beginning TeX programming I don't understand how to do this.
>>     
>
> Elliot,
>
> You can use \doif{\getvalue{set}{var}}{value} for simple string 
> comparisons. See http://wiki.contextgarden.net/System_Macros for basic 
> flow control features of ConTeXt.
>
> It may also be possble to see if variables have changed using setups 
> http://wiki.contextgarden.net/Inside_ConTeXt#Using_setups_for_namespaces 
> but I have never personally used that.
>   
these test if the variable has been set (defined test):

\doifelsevariable#1#2
\doifvariable#1#2
\doifnotvariable#1#2

(is not the same as test for empty)

there is also:

\getvariabledefault#1#2#3

with #3 being a default value for when undefined

Hans


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Re: Test whether variable has been set

[Peter Rolf]

Elliot Clifton schrieb:
> Hi Peter,
> 
> Thanks for your reply. I think I may have misunderstood the variable
> section on the wiki. I been using \setvariable to both declare and
> assign variables from my component files. When I should have been
> declaring them in the environment file first, right?

As long as you can garantee, that your variables are declared *before*
they are read, things are ok. But an environment or extra file is IMO
the cleanest way.

Reading an undefined variable results in the \empty token. This can be
problematic, if you expect a number; e.g.
\dimexpr\getvariable{foo}{width}\relax.

Anyway, it's no good idea to use something that is not defined.

So you have to
  - define a variable, before you use it  or
  - use the \doifnotvariable,\doifvariable and \doifelsevariable macros
before you try to read a (maybe undefined) variable.

I can't say much about the second one. Search the ConTeXt sources to get
an idea.

The \doifnothing,\doifsomething and \doifelsenothing macros just test,
if the variable is empty or not.
A variable can be defined with an empty value (\setvariable[foo][bar=]).
I use this for automatic size calculations. If no default value is
given, then the size is calculated in my macro.


> \setvariable[namespace][key=DefaultValue], right? So how do I test for
> a (Default)Value?

\doifsamestring{\getvariable{foo}{bar}} {your_default_value}
  {equal}%
\doifsamestringelse{\getvariable{foo}{bar}} {your_default_value}
  {equal}
  {unequal}%

probably not the fastest variant. If I remember it right, I had some
problems with \doif comparison (catcodes?).

> Sorry, I'm just beginning TeX programming I don't understand how to do this.
>
No problem. If it's not in the WIKI, this is the place to ask.


Best, Peter

> Elliot
> ___________________________________________________________________________________
> If your question is of interest to others as well, please add an entry to the Wiki!
> 
> maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
> webpage  : http://www.pragma-ade.nl / http://tex.aanhet.net
> archive  : https://foundry.supelec.fr/projects/contextrev/
> wiki     : http://contextgarden.net
> ___________________________________________________________________________________
> 

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___________________________________________________________________________________

Re: Test whether variable has been set

[Peter Rolf]

Hi Elliot,

Elliot Clifton schrieb:
> Hi,
> 
> How can test whether a variable has been set? I couldn't find any
> reference to this in the wiki?
>
What do you mean by "set"?

I use

\doifnothing{\getvariable{foo}{bar}}
  {foo:bar contains nothing.\par}%
\doifsomething{\getvariable{foo}{bar}}
  {foo:bar contains something.\par}%
\doifelsenothing{\getvariable{foo}{bar}}
  {foo:bar contains nothing.\par}
  {foo:bar contains something.\par}%

to test, if a defined(!) variable contains something.

If you want to test if a variable is defined, you can use

\doifnotvariable{foo}{bar}
  {foo:bar is undefined.\par}%
\doifvariable{foo}{bar}
  {foo:bar is defined.\par}%
\doifelsevariable{foo}{bar}
  {foo:bar is defined.\par}
  {foo:bar is undefined.\par}%

Never used these macros, as I always define default values for my variables.


HTH, Peter


> TIA,
> 
> Elliot
> ___________________________________________________________________________________
> If your question is of interest to others as well, please add an entry to the Wiki!
> 
> maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
> webpage  : http://www.pragma-ade.nl / http://tex.aanhet.net
> archive  : https://foundry.supelec.fr/projects/contextrev/
> wiki     : http://contextgarden.net
> ___________________________________________________________________________________
> 

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___________________________________________________________________________________

Test whether variable has been set

[Elliot Clifton]

Hi,

How can test whether a variable has been set? I couldn't find any
reference to this in the wiki?

TIA,

Elliot
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