Haskell相当于Ruby的slice_when

Question

我是Haskell的新手,我想要一个像Ruby的slice_when一样的函数:

slice_when Ruby

a = [1,2,4,9,10,11,12,15,16,19,20,21]
b = a.slice_when {|i, j| i+1 != j }
p b.to_a #=> [[1, 2], [4], [9, 10, 11, 12], [15, 16], [19, 20, 21]]

哈斯克尔

ghci > slice_when (\x y -> x+1 /= y) [1,2,4,9,10,11,12,15,16,19,20,21] 

=> [[1, 2], [4], [9, 10, 11, 12], [15, 16], [19, 20, 21]]

非常感谢你.

Answer 1

这是一个sliceWhen我相信你想要的实现:

sliceWhen :: (a -> a -> Bool) -> [a] -> [[a]]
sliceWhen _ []  = []
sliceWhen _ [x] = [[x]]
sliceWhen f (x:y:xs)
  | f x y     = [x] : sliceWhen f (y:xs)
  | otherwise = let z:zs = sliceWhen f (y:xs)
                in (x:z) : zs

上面的函数在每个边界上运行提供的谓词,如果返回True,则创建一个接缝.否则,它会将"当前"值固定到列表其余部分的第一个元素上.