Lofting Curves

        vector uv = vertex(0, 'uv', i@vtxnum);
vector uvw = set(uv[0], 0.0, 0.0);

int prims[] = expandprimgroup(1, '*');
vector pos[];
foreach(int pr; prims){
    vector pos_pr = primuv(1, 'P', pr, uvw);
    append(pos, pos_pr);
}

// De Casteljau
vector p[] = pos;
int n = len(p);

while(n > 1){
    for(int i = 0; i < n - 1; i++){
        p[i] = lerp(p[i], p[i+1], uv[1]);
    }
    n--;
}

v@P = p[0];