Dynamic 在Haskell中动态构建列表理解

我很好奇是否可以在Haskell中动态构建列表理解

例如，如果我有以下内容：

all_pows (a,a') (b,b') = [ a^y * b^z | y <- take a' [0..], z <- take b' [0..] ]

然而，我真正想要的是

all_pows [(Int,Int)] -> [Integer]

---

这样我就可以支持

N

对参数，而无需构建

N

版本的

all\u-pows

。我对Haskell还是个新手，所以我可能忽略了一些显而易见的事情。这可能吗？

单子列表的魔力：

ghci> let powers (a, b) = [a ^ n | n <- [0 .. b-1]] ghci> powers (2, 3) [1,2,4] ghci> map powers [(2, 3), (5, 3)] [[1,2,4],[1,5,25]] ghci> sequence it [[1,1],[1,5],[1,25],[2,1],[2,5],[2,25],[4,1],[4,5],[4,25]] ghci> mapM powers [(2, 3), (5, 3)] [[1,1],[1,5],[1,25],[2,1],[2,5],[2,25],[4,1],[4,5],[4,25]] ghci> map product it [1,5,25,2,10,50,4,20,100] ghci> let allPowers list = map product $ mapM powers list ghci> allPowers [(2, 3), (5, 3)] [1,5,25,2,10,50,4,20,100] 或者使用折叠

import Data.List
product list = foldl' (*) 1 list

---

但实际上，它已经被定义了！我喜欢这种语言☺☺☺

让powers（a，b）=[a^n | n@Tordek谢谢，我略过了原文有点太快了。
cartesianProduct :: [[a]] -> [[a]]
cartesianProduct [] = [[]]
cartesianProduct (list:lists)
  = [ (x:xs) | x <- list, xs <- cartesianProduct lists ]

product list = product' 1 list
  where product' accum [] = accum
        product' accum (x:xs)
          = let accum' = accum * x
             in accum' `seq` product' accum' xs

import Data.List
product list = foldl' (*) 1 list