func insert_after(a,b) {
b{:next} = a{:next};
a{:next} = b;
}
var B = Hash.new(
data => 3,
next => nil, # not a circular list
);
var A = Hash.new(
data => 1,
next => B,
var C = Hash.new(
data => 2,
insert_after(A, C);