[metapost] Cannot fill sector

[Yasir Malik]

Hi,

I'm having trouble filling a sector.  Metapost does not return an error, 
but the "area" path is not filled.  Here's my code:

beginfig(1);

u = 1cm;

pair o, p[];
path halfcirc, area, triangle;
numeric diam;

diam = 10u;

o := (0, 0);
p0 := (diam/2, 0);
p0 := p0 rotated 72; % a cycle cannot be formed with 10 degrees
p1 := p0 rotated 72;
triangle = p0--o--p1;

halfcirc = halfcircle scaled diam;

draw halfcirc;
draw triangle;

area = buildcycle(triangle, halfcirc);
fill area withgreyscale .7;


endfig;


Also, as I note in the comment, if I rotate p0 by 10 degrees, Metapost 
says the two paths do not intersect.

I appreciate your help.

Thanks,
Yasir