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% language=uk
%
% copyright=pragma-ade readme=readme.pdf licence=cc-by-nc-sa
\startcomponent metafun-conventions
\environment metafun-environment
\startchapter[title={Conventions}]
\startsection[title={Suffixes}]
One characteristic of using \METAFUN\ in \CONTEXT\ is that it is basically one
long run. The code snippets become figures that then get converted to \PDF\ and
embedded. If text is involved, each figure is actually processed twice, once to
identify what needs to be typeset, and once with the result(ing metrics).
Normally that gets unnoticed. You can check for the state by consulting the
boolean \type {mfun_trial_run}.
A consequence of the one run cq.\ multiple runs is that you need to be careful with
undefined or special variables. Consider the following:
\starttyping
vardef foo@#(text t) =
save s ; string s ; s := str @# ;
if length(s) > 0 :
textext(s)
else :
nullpicture
fi
enddef ;
\stoptyping
The following works ok in the first run when bar is undefined:
\starttyping
draw foo.bar("a") ;
\stoptyping
But if afterwards we say:
\starttyping
vardef bar(expr x) =
123
enddef ;
\stoptyping
and expand \type {foo.bar} again we will get an error message because this time
\type {bar} expands. Suffixes are always expanded!
The lesson is: when you get unexpected results or errors, check your variable
definitions. You can use the \type {begingroup} and \type {endgroup} primitives
to protect your variables but then you also need to explicitly use \type {save}
to store their meanings and allocate new ones after that inside the group.
\stopsection
\stopchapter
\stopcomponent
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