打印由Com返回Haskell的整数列表二进制生成.组合

我在 http://www.polyomino.f2s.com/david/haskell/combinatorics.html

我在该模块中使用的源代码是:

combinationsOf 0 _ = [[]]
combinationsOf _ [] = []
combinationsOf k (x:xs) = map (x:) (combinationsOf (k-1) xs)
                          ++ combinationsOf k xs

combinations k n = combinationsOf k [1..n]

我添加了以下签名,看看这是否会产生影响,但事实并非如此:

combinationsOf :: Integer -> [a] -> [[a]]
combinations :: Integer -> Integer -> [[Integer]]

我的Haskell源文件是:

module Main
    where
        import IO
        import qualified CombinatoricsGeneration as CG

        main = putStr $ unlines $ map show CG.combinations(6, 8)

$ ghc --version
The Glorious Glasgow Haskell Compilation System, version 6.12.3
$ ghc -c CombinatoricsGeneration.hs 
$ ghc -o test  CombinatoricsGeneration.o test.hs 

test.hs:6:37:
Couldn't match expected type `[a]'
       against inferred type `t -> t1 -> [[t1]]'
In the second argument of `map', namely `CG.combinations'
In the second argument of `($)', namely
    `map show CG.combinations (6, 8)'
In the second argument of `($)', namely
    `unlines $ map show CG.combinations (6, 8)'

main = putStr $ unlines $ map show [[1,2],[2],[3]]

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