pbsz
if(mech->pbsz)
new = (*mech->pbsz)(app_data, size);
void pbsz (int);
size_t (*pbsz)(void *, size_t);
pbsz((yyvsp[(3) - (5)].i));
pbsz($3);
if(mech->pbsz)
new = (*mech->pbsz)(app_data, size);