, reverse -- :: [a] -> [a]
, intersperse -- :: a -> [a] -> [a]
+ , intercalate -- :: [a] -> [[a]] -> [a]
, transpose -- :: [[a]] -> [[a]]
-- * Reducing lists (folds)
-- ** The \"@By@\" operations
-- | By convention, overloaded functions have a non-overloaded
-- counterpart whose name is suffixed with \`@By@\'.
+ --
+ -- It is often convenient to use these functions together with
+ -- 'Data.Function.on', for instance @'sortBy' ('compare'
+ -- \`on\` 'fst')@.
-- *** User-supplied equality (replacing an @Eq@ context)
-- | The predicate is assumed to define an equivalence.
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,
--