[metapost] nonstopmode interaction

[Troy Henderson]

Here is my dilemma.  I have written a homemade function grapher (which
currently does only 3D function surface plots but will eventually do 2D
function plots, 2D and 3D parametric curves/surfaces, and perhaps more).

http://www.tlhiv.org/mpgraph/ (Only tested in Mozilla Firefox currently)

The user provides a function, a domain (and optional range) as well as
several other tweaks for the graph.  One of the tweaks is how the x,y, and z
axes are labeled.  Everything is computed internally with Perl (CGI) and
Perl simply writes a MetaPost file that stores everything (filled paths,
stroked paths, labels, etc.).  The only thing that the user can "break" in
the MetaPost file is providing a x,y,z axis label (using TeX code) that does
not typeset.  Everything else is generated safely with the Perl script.

So, I would like to either

1) have MetaPost continue through compilation errors caused by the labels
resulting in a nice picture without labels (which seems unlikely)

2) have some way to let the user know that a label has failed (which seems
doable, I'm just not clear how to do this)

I would appreciate any ideas that anyone may have.

Troy
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