# [NTG-context] Conditional text appearing in a fixed vertical space

Fabrice L fabrice.alpha at gmail.com
Wed Jan 12 00:13:55 CET 2022

> Le 11 janv. 2022 à 17:56, Gavin via ntg-context <ntg-context at ntg.nl> a écrit :
>
> Thanks Hans! This is great. I made a slight change to add an additional feature. By moving the “mysolution” definition out of \startmode[solution], I can now use mysolution in either mode. I’d use this if I want to give my solution to one of the problems, as an example, on the handout.
>
> -Gavin

I have similar problem for my courses. The solution I use, different than the one offered, is to write in a « special » color the text I want to hide from the students. This permits me to have hidden texts in figures for exemple. Also, I do not calculate space required, this is automated !  Here is MWE :

\enablemode[solution]

\doifmode{solution}{
\definecolor[solcolor][magenta]
}
\doifnotmode{solution}{
\definecolor[solcolor][white]
}
\definedescription[solution]
[color=solcolor]

\starttext

How many roads? \startcolor[solcolor] Professor note.\stopcolor
\startsolution
\stopsolution

How much wood?
\startsolution
Alotta wood!
\stopsolution

No more questions.

\stoptext

So the color used when solutions are hidden are white on white, we can not see the text;  but of course, if you change the background, you see the hidden text. So there is another step to the process (I usually do this only once a term); open the file in Acrobat, and find the option to delete hidden text. The text for which the color is the same as the background is really deleted. You can try to select the text in any pdf view/editor, the text is gone !

Fabrice.

>
>
> % \enablemode[solution]
>
> % Define "mysolution” for use independent of solution mode.
> \definenarrower[mysolution]
>  [before=\blank\it,
>   after=\blank]
>
> % If in solution mode, define "solution" to use "mysolution"
> \startmode[solution]
>   \tolerant\protected\def\startsolution[#1]%
>     {\startmysolution}
>   \protected\def\stopsolution
>     {\stopmysolution}
> \stopmode
>
> % If NOT in solution mode, define "solution" to produce a blank space
> \startnotmode[solution]
>   \tolerant\protected\def\startsolution[#1]%
>     {\doifelsenothing{#1}{\blank[1in]}{\blank[#1]}
>      \gobbleuntil\stopsolution}
>   \protected\def\stopsolution
>     {}
> \stopnotmode
>
>
> \starttext
>
>  \startsolution
>  \stopsolution
>
> How much wood?
>  \startsolution[1.5in]
>    Alotta wood!
>  \stopsolution
>
> No more questions.
>
> \stoptext
>
>
>> On Jan 11, 2022, at 1:13 PM, Hans Hagen <j.hagen at xs4all.nl> wrote:
>>
>> On 1/11/2022 8:50 PM, Gavin via ntg-context wrote:
>>> Hello List,
>>> I am making problem sets for a physics class. Solutions use the style defined in the example below, and only appear if the “solution” mode is enabled. I am struggling to get a vertical space for the solution which is the same whether or not the solution is printed. Different problems require different amounts of space, so this should be an argument or key-value.
>>> In the example below, the first solution has the desired behavior. The second solution has the syntax I’d like, but it doesn’t make the space without a solution.
>>> Any ideas would be welcome! I am still pretty new to ConTeXt, so I struggle mixing things like the plain tex \vbox and ConTeXt \start…\stop concepts.
>>> Thanks,
>>> Gavin
>>> \definemode[solution][yes] % yes to enable solutions, no to disable
>>> \definebuffer  [solution] % Captures solution in a buffer that isn't used
>>> \startmode[solution] % If in solution mode, redefine \startsolution...\stopsolution
>>> \definedelimitedtext[solution][ % Solution italic and indented
>>>  spacebefore=medium,
>>>  spaceafter=medium,
>>>  style=\rm\it,
>>>  leftmargin=standard, % Indents block on the left
>>>  rightmargin=yes, % Indents block on the right
>>>  indentnext=no,
>>>  before=\vbox to 1in\bgroup,
>>>  after=\egroup,
>>> ]
>>> \stopmode
>>> \starttext
>>> How many roads? (The 1-inch space below appears whether or not it contains a solution.)
>>> \vbox to 1in{%
>>>  \startsolution
>>>  \stopsolution
>>> }
>>> How much wood? (I would like to define solution so this to behaves like the previous question.)
>>> \startsolution[1in]
>>>  Alotta wood!
>>> \stopsolution
>>> No more questions.
>>> \stoptext
>> a mix between big and low level
>>
>> % \enablemode[solution]
>>
>> \startmode[solution] % If in solution mode, redefine \startsolution...\stopsolution
>>
>>   \definenarrower
>>     [mysolution]
>>     [before=\blank,
>>      after=\blank]
>>
>>   \tolerant\protected\def\startsolution[#1]%
>>     {\startmysolution
>>      \it}
>>
>>   \protected\def\stopsolution
>>     {\stopmysolution}
>>
>> \stopmode
>>
>> \startnotmode[solution] % If in solution mode, redefine \startsolution...\stopsolution
>>
>>   \tolerant\protected\def\startsolution[#1]%
>>     {\doifelsenothing{#1}{\blank[2.5cm]}{\blank[#1]}
>>      \gobbleuntil\stopsolution}
>>
>>   \protected\def\stopsolution
>>     {}
>>
>> \stopnotmode
>>
>> \starttext
>>
>> How many roads? (The 1-inch space below appears whether or not it contains a solution.)
>>
>> \startsolution
>> \stopsolution
>>
>> How much wood? (I would like to define solution so this to behaves like the previous question.)
>>
>> \startsolution[1in]
>>   Alotta wood!
>> \stopsolution
>>
>> No more questions.
>> \stoptext
>>
>> much nicer is to use the blocks mechanism (but i need to check if we can do the 2in there)
>>
>> Hans
>>
>> -----------------------------------------------------------------
>>                                         Hans Hagen | PRAGMA ADE
>>             Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
>>      tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
>> -----------------------------------------------------------------
>
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