[metapost] Arrows in the middle of a path

[Troy Henderson]

>   def midarrow (expr p, t) =
>     drawarrow subpath(0,t) of p;
>     draw subpath(t,1) of p;
>   enddef;

I might do something like

   def midarrow (expr p, t) =
     drawarrow subpath(0,t*length(p)) of p;
     draw subpath(t,length(p)) of p;
   enddef;

and this works for paths of length greater than 1.  The parameter t is
now a percentage of the total "path time".

Troy