Metapost: return value of vardef macros

Question

Can we return a path or picture from a vardef macros? And how to call the return value? Google said "the last statement has no semicolon; its value is returned by the function". My purpose is to repeat using the path or picture. Followed is a small code. But it failed. Maybe I misunderstood something. Please note that the returned path or picture might not need to be drawn out. It might be used to help to construct something else, e.g., help to find intersection point.

vardef foo (expr from, to) =
  path p;
  p = from -- to
enddef;

beginfig(1)
  path p;
  pair A, B;
  A = (0,0);
  B = (1,1);
  p = foo (A, B);
  draw p;
endfig;

Answer 1

You can, and there is no need to specify the type of the returned object or even to give it a name. This should work for you as well:

vardef foo (expr from, to) =
  from -- to
enddef;

beginfig(1)
  path p;
  pair A, B;
  A = (0,0);
  B = cm*(1,1);
  p = foo (A, B);
  draw p;

endfig;
end.

Edit: here is an equivalent but much shorter coding of the same program, without variables which are unnecessary in this simple case.

vardef foo (expr from, to) =
  from -- to
enddef;

beginfig(1)
  draw foo (origin, cm*(1,1));
endfig;
end.