Is it possible to have some explanation of the parameters of the macro numberstriped(#1,#2,#3) ?
How to have horizontal hatching ? (How to change the slope hatching ?)

There is also anglestriped in mp-tool with some examples. The second argument changes the angle.

\startMPpage[offset=2mm]

path p, q ;

p := unitsquare scaled 4cm ;

z1 = point 3.6 of p ;

q := subpath (0,2) of p -- z1 -- cycle;

q := q shifted(-4cm,-4cm);

draw q anglestriped(1,180,6) withcolor blue;

draw p ;

\stopMPpage

(I have not yet found why the striped path q goes out of position. Looking at mp-tool may help.)

I just noticed that the position of labels is not quite the same when using macros and macro Metafun Metapost:
I think the labels are too near to the corners of the square with the macro Metafun.