[metapost] Error when defining a function

[Taco Hoekwater]

Peng Yu wrote:
> Hi
> 
> I couldn't figure out what is wrong with the following metapost
> program. Would you please help me?

The formal macro arguments should be single symbolic tokens, not
sequences (x1 is essentially 'x', followed by '1').

In this case, I would propose you use

def drawrect(expr lx, rx, by, ty) =
  draw (lx,by)--(rx,by)--(rx,ty)--(lx,ty)--cycle
enddef;

Best wishes, Taco