-{-# OPTIONS -fno-implicit-prelude #-}
+{-# OPTIONS_GHC -fno-implicit-prelude #-}
-----------------------------------------------------------------------------
-- |
-- Module : Data.List
, reverse -- :: [a] -> [a]
, intersperse -- :: a -> [a] -> [a]
+ , intercalate -- :: [a] -> [[a]] -> [a]
, transpose -- :: [[a]] -> [[a]]
-- * Reducing lists (folds)
-- ** Predicates
, isPrefixOf -- :: (Eq a) => [a] -> [a] -> Bool
, isSuffixOf -- :: (Eq a) => [a] -> [a] -> Bool
+ , isInfixOf -- :: (Eq a) => [a] -> [a] -> Bool
-- * Searching lists
isSuffixOf :: (Eq a) => [a] -> [a] -> Bool
isSuffixOf x y = reverse x `isPrefixOf` reverse y
+-- | The 'isInfixOf' function takes two lists and returns 'True'
+-- iff the first list is contained, wholly and intact,
+-- anywhere within the second.
+--
+-- Example:
+--
+-- >isInfixOf "Haskell" "I really like Haskell." -> True
+-- >isInfixOf "Ial" "I really like Haskell." -> False
+isInfixOf :: (Eq a) => [a] -> [a] -> Bool
+isInfixOf needle haystack = any (isPrefixOf needle) (tails haystack)
+
-- | The 'nub' function removes duplicate elements from a list.
-- In particular, it keeps only the first occurrence of each element.
-- (The name 'nub' means \`essence\'.)
intersperse _ [x] = [x]
intersperse sep (x:xs) = x : sep : intersperse sep xs
+-- | 'intercalate' @xs xss@ is equivalent to @('concat' ('intersperse' xs xss))@.
+-- It inserts the list @xs@ in between the lists in @xss@ and concatenates the
+-- result.
+intercalate :: [a] -> [[a]] -> [a]
+intercalate xs xss = concat (intersperse xs xss)
+
-- | The 'transpose' function transposes the rows and columns of its argument.
-- For example,
--