undiagnosed pic error

[Douglas McIlroy]

Pic knows how to fill a box, a circle or an ellipse.
Groff(7) says you can fill "closed drawn objects".
So, on a whim, I tried to fill a triangle by drawing a closed line.

.PS
line from 0,0 to 0,1 to 1,1 to 0,0 fill 0.5
.PE

The line is drawn but not filled, and no diagnostic  is
issued for the inapplicable "fill".

A nice fix would be to make filled polygons work, perhaps
with a keyword "polygon", which behaves like "line", but
closes the figure automatically. Self-crossing polygons can
be handled as in PostScript.

A super-duper fix would support filling of closed curves made
of lines, splines and arcs.

In any event, it is wrong to silently ignore "fill".

Doug