I'm trying to draw some random arrows using Metapost. For that I use a piece of code from fpast that in found at stackexchange

Unfortunately this code does not work in context (request for a solution) because the freelabel() function. If I disable it the result is the expected.

What is wrong with this code?

\starttext

\startMPcode

numeric u, nb_vectors, wd;

u := 1cm; % unit length

nb_vectors := 20; wd = .5;

boolean intersect; pair random_origin; color random_color; path candidate, random_vector[];

vardef bb(expr p) =

save orig, extr; pair orig, extr; orig = point 0 of p; extr = point 1 of p;

pair v,w; v = wd*unitvector(extr-orig)*u; w = v rotated 90;

(orig - v + w) -- (extr + v + w) -- (extr + v - w) -- (orig - v - w) -- cycle

enddef;

pickup pencircle scaled 2bp;

i = 1;

forever:

exitunless (i <= nb_vectors);

intersect := false;

random_length := u*(2+uniformdeviate(1));

random_angle := uniformdeviate(359);

random_origin := u*(uniformdeviate(wd*nb_vectors), uniformdeviate(wd*nb_vectors));

random_color := (uniformdeviate(1), uniformdeviate(1), uniformdeviate(1));

candidate := random_origin -- (random_origin + random_length*dir(random_angle));

j := 1;

forever:

exitif (j = i) or (intersect = true);

if bb(random_vector[j]) intersectiontimes bb(candidate) <> (-1, -1):

intersect := true;

fi;

j := j+1;

endfor;

if intersect = false:

random_vector[i] = candidate;

drawarrow candidate withcolor random_color;

freelabel(btex $v$ etex, point .5 of candidate, point .5 of candidate + dir (random_angle + 90));

i := i+1;

fi;

endfor;

\stopMPcode

\stoptext