function fib_closure()
  local a = 1
  local b = 1
  return function()
    local v = a
    a, b = b, b + v
    return v
  end
end

function fib_ite_expand ()
   local a = 1
   return function (_, b)
      v = a
      a = b
      return (v + b), v
   end, nil, 1
end

function fib_stateless()
   local state = {a = 1, b = 1}
   return function (st)
      v = st.a
      st.a, st.b = st.b, st.b + v
      return v
   end, state
end