The use of the Y Combinator to enable true memoization of a recursive function has been discussed on the 'net a number of times. I used the mockingbird version

The use of the Y Combinator to enable true memoization of a recursive function has been discussed on the 'net a number of times. I used the mockingbird version for a very specific purpose in production a while back, although that was more like corecursion than recursion.