@@ -77,8 +77,8 @@ module Data.Text.Lazy
7777 -- * Construction
7878
7979 -- ** Scans
80− -- , scanl
81− -- , scanl1
80+ , scanl
81+ , scanl1
8282 -- , scanr
8383 -- , scanr1
8484
@@ -424,6 +424,29 @@ minimum :: Text -> Char
424424minimum t = S.minimum (stream t)
425425{-# INLINE minimum #-}
426426
427+-- | /O(n)/ 'scanl' is similar to 'foldl', but returns a list of
428+-- successive reduced values from the left. This function is subject
429+-- to array fusion.
430+--
431+-- > scanl f z [x1, x2, ...] == [z, z `f` x1, (z `f` x1) `f` x2, ...]
432+--
433+-- Note that
434+--
435+-- > last (scanl f z xs) == foldl f z xs.
436+scanl :: (Char -> Char -> Char) -> Char -> Text -> Text
437+scanl f z t = unstream (S.scanl f z (stream t))
438+{-# INLINE scanl #-}
439+
440+-- | /O(n)/ 'scanl1' is a variant of 'scanl' that has no starting
441+-- value argument. This function is subject to array fusion.
442+--
443+-- > scanl1 f [x1, x2, ...] == [x1, x1 `f` x2, ...]
444+scanl1 :: (Char -> Char -> Char) -> Text -> Text
445+scanl1 f t0 = case uncons t0 of
446+ Nothing -> empty
447+ Just (t,ts) -> scanl f t ts
448+{-# INLINE scanl1 #-}
449+
427450-- | /O(n)/ 'splitAt' @n t@ returns a pair whose first element is a
428451-- prefix of @t@ of length @n@, and whose second is the remainder of
429452-- the string. It is equivalent to @('take' n t, 'drop' n t)@.