Haskell数据结构

Question

我正在尝试在Haskell中构建一个数据结构,其中的函数可以用来避免重新计算值.例如,假设我有这个功能:

f :: Int -> Int -> Int
f 1 1 == 1
f m n
    | abs m > n = 0
    | OTHERWISE if value of f m n has already been computed by another recursive branch, return that value and add it to the "database"
    | OTHERWISE return f (m-1) (n-1) + f (m - 1) n

我已经看过memoization,但还没能实现解决方案:

建议？:)

Answer 1

这里有一个很好的解释.

我喜欢memoize包:)

示例(解决"青蛙正在跳楼梯......"问题):

import Data.Function.Memoize 

ladder :: Integer -> Integer -> Integer 
ladder n k = g n 
  where g = memoize f 
        f 0 = 1 
        f x = sum [g (x - y) | y <- [1..if x < k then x else k]]