question about vardef variables

[Damien Thiriet <damien@thiriet.web4me.fr>]

Hi,


I have some troubles with understanding metafun's macro mechanism.

Given this MWE:

\starttext
\startMPpage

vardef Test (expr ab,cd)=
   %numeric ab;
   %numeric cd;
   draw unitsquare scaled 10 xshifted ab;
   draw unitsquare scaled 10 yshifted cd;
enddef;

Test (50,100);
\stopMPpage
\stoptext

Uncommenting the two declarations makes me run intro a silent error. I was 
lucky enough yesterday to get an explicit error message with a more 
complex macro.  It made me figure out where my problems came from.

So here are my two questions:
- Why shouldn't we tell metafun if expr is a path, a pair or so on?
- Would it be possible to issue an error message each time this wrong
declaration is made?

Thanks,


Damien Thiriet 
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