there have a lot of situation we need memorize intermediate computation value. 

and use in further.

like this, compute nth fib question.

So,how memorize it?

i have an ugly solution.it used HashTable for memorization.

fib n table

 | n==1 =1

 | n==2 =1

 | otherwise =

  case lookup table of

    Just v   ->(v,table)

    Nothing ->let (v,table') = fib (n-1) table in

                   let ( v',table'')= v + fib(n-2) table' in

                   (v',table'')

i am an beginner come from imperative programming language.

so fib memorize version program hurt my brain ... particular in Nothing branches.

so do you have some good idea