function insert (b, node, value) {
  return updateNext(b, node, cons(b, value, readNext(b, node)))
}
function insert (b, node, value) {
  return updateNext(b, node, cons(b, value, readNext(b, node)))
}
function insert ( b , node , value ) { return updateNext ( b , node , cons ( b , value , readNext ( b , node ) ) ) }
insert value into a list after node.
insert value into a list after node .