Hi all,
cleaning up the code in my module, I run into a very interesting
problem. I want to pass a user-defined value to Metapost. Until now,
the value "scale" had to be numeric, and I used it like this:
draw fullcircle scaled \MPvar{scale}mm
and Metapost was happy, and I was too. Now Aditya made the reasonable
suggestion that users should be allowed to input any dimension and not
be restricted to "mm." Easy enough. However, I also want a fallback
just in case they input a number, in that case, I want to fall back to
mm as a default. So I tried (after Taco's excellent explanation on the
wiki):
\expandafter\processaction\expandafter[\CVERscale]%
[\v!unknown=>{\doifdimensionelse%
{\CVERscale}%
{\setupMPvariables[CircleSomething][scale=\CVERscale]}%
{\doifnumberelse%
{\CVERscale}%
{\newdimen\CIscale \global\CIscale=\CVERscale mm
{\setupMPvariables[CircleSomething][scale=\the\CIscale]}}%
{\setupMPvariables[CircleSomething][scale=10mm\relax]%
\message{Please give a proper value for the "scale"
argument!}}}},
\v!default=>{\setupMPvariables[CircleSomething][scale=10mm
\relax]}]
So what I want: first check if \CVERscale is a dimension; if it is,
assign it to the "scale" parameter. If it isn't, check if it is a
number; if this is the case, append the unit "mm" to it and put it
into a dimension register. If it isn't a number either, make the value
sufficiently absurd for the user to realize and write a message to the
terminal. This is all fine and dandy and works, sort of: it works
perfectly with dimensions, but when I try with a number as input, it
doesn't fall back to the unit "mm," but to "pt," AFAICS. That's nice
too, but I have no clue why, and I would prefer mm. If it helps, I can
try to give you a minimal test file tomorrow, but maybe somebody spots
what I'm doing wrong? (I tried both with mkii and mkiv, and always get
the same result.)
All best
Thomas
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