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

[Hans Hagen]

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
>      42 roads.
>    \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
     42 roads.
\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
-----------------------------------------------------------------