From: Peter Rolf <peter.rolf@arcor.de>
Subject: Re: variables
Date: Wed, 16 Jul 2003 11:11:38 +0200 [thread overview]
Message-ID: <3F1516CA.1000007@arcor.de> (raw)
In-Reply-To: <20030715162223.5116578c.taco@elvenkind.com>
Thank you Taco for your exact answer. I will use \doifelse instead :)
Regards,
Peter
Taco Hoekwater wrote:
>On Tue, 15 Jul 2003 14:59:44 +0200, Peter wrote:
>
>
>
>>I want to test, if a given variable is empty or not. I tried the following,
>>but the test is always false. Is this a bug or a feature ;)
>>
>>
>
>It is a feature/bug of TeX itself that "\if" tests perform a conditionality test
>that is not even remotely intuitive ;-)
>
>The '\if' looks ahead to see if the next two non-expandable tokens have
>the same 'character code' *after* expansion. It will actually compare 's'
>to 'o' in the "second" example (false). The input "second=oops" would have
>given a 'true' result, but would also have typeset the extra letters ('ps') as a
>side-effect.
>
>TeX's \if test can be quite confusing and should normally not
>be used in a document. It is much better to use one of ConTeXt's
>predefined commands, like this one:
>
> \doifelse
> {\TestVAR{first}}
> {}
> {The variable test:first is empty.}
> {The variable test:first contains \TestVAR{first}.}
>
>this compares argument #1 to argument #2, executing #3 or #4 depending
>on the outcome of the test.
>
>Greetings, Taco
>
>
>
>>Any help is welcome.
>>
>>
>>\starttext
>>
>>\setvariables[test]
>> [first=,
>> second=something,]
>>
>>\def\TestVAR#1{\getvariable{test}{#1}}
>>
>>\if\TestVAR{first}\empty %
>> The variable test:first is empty.\else
>> The variable test:first contains \TestVAR{first}.\fi
>>
>>\if\TestVAR{second}\empty %
>> The variable test:second is empty.\else
>> The variable test:second contains \TestVAR{second}.\fi
>>
>>\stoptext
>>
>>
>>Regards,
>>
>> Peter
>>
>>
>>_______________________________________________
>>ntg-context mailing list
>>ntg-context@ntg.nl
>>http://www.ntg.nl/mailman/listinfo/ntg-context
>>
>>
>
>
>
>
prev parent reply other threads:[~2003-07-16 9:11 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-07-15 12:59 variables Peter Rolf
2003-07-15 14:22 ` variables Taco Hoekwater
2003-07-16 9:11 ` Peter Rolf [this message]
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