module Misc where

-- from ghc data.list, which isn't in yhc.

intersperse:: a -> [a] -> [a]
intersperse _   []      = []
intersperse _   [x]     = [x]
intersperse sep (x:xs)  = x : sep : intersperse sep xs

transpose               :: [[a]] -> [[a]]
transpose []             = []
transpose ([]   : xss)   = transpose xss
transpose ((x:xs) : xss) = (x : [h | (h:t) <- xss]) : transpose (xs : [ t | (h:t) <- xss])


isInfixOf               :: (Eq a) => [a] -> [a] -> Bool
isInfixOf needle haystack = any (isPrefixOf needle) (tails haystack)
tails                   :: [a] -> [[a]]
tails []                =  [[]]
tails xxs@(_:xs)        =  xxs : tails xs
isPrefixOf              :: (Eq a) => [a] -> [a] -> Bool
isPrefixOf [] _         =  True
isPrefixOf _  []        =  False
isPrefixOf (x:xs) (y:ys)=  x == y && isPrefixOf xs ys

-- containers