MetaFun - Pragma ADE

A different approach is to use a two dimensional array. In doing so, we can access the variables
more easily using loops. If we omit the labels, and angle macro, the previously defined macro can
be reduced considerably.
def draw_problem (expr n, p, q, r, s) = % number and 4 positions
begingroup ; save x, y ;
z[1][1] = p ; z[2][1] = q ; z[3][1] = r ; z[4][1] = s ;
for i=1 upto 4 :
z[i][1] = (x[i][1],y[i][1]) = z[if i=1: 4 else: i-1 fi][2] ;
z[i][2] = (x[i][2],y[i][2]) ;
z[i][3] = (x[i][2]-y[i][2]+y[i][1], y[i][2]+x[i][2]-x[i][1]) ;
z[i][4] = (x[i][1]-y[i][2]+y[i][1], y[i][1]+x[i][2]-x[i][1]) ;
z[i] = 0.5[z[i][1],z[i][3]] ;
endfor ;
z[0] = whatever[z[1],z[3]] = whatever[z[2],z[4]] ;
pickup pencircle scaled .5pt ;
for i=1 upto 4 :
draw z[i][1]--z[i][2]--z[i][3]--z[i][4]--cycle ;
draw z[i][1]--z[i][3] ; draw z[i][2]--z[i][4] ;
if i