3 files changed, 12 insertions(+), 7 deletions(-)

M src/Data/Text/ParagraphLayout/Plain.hs
M src/Data/Text/ParagraphLayout/Run.hs
M src/Data/Text/ParagraphLayout/TextContainer.hs

@@ 101,6 101,8 @@ instance Functor WithSpan where
 
 instance TextContainer a => TextContainer (WithSpan a) where
     getText (WithSpan _ c) = getText c
+
+instance SeparableTextContainer a => SeparableTextContainer (WithSpan a) where
     splitTextAt8 n (WithSpan rs c) = (WithSpan rs c1, WithSpan rs c2)
         where (c1, c2) = splitTextAt8 n c
 

@@ 30,6 30,8 @@ data Run = Run
 
 instance TextContainer Run where
     getText = runText
+
+instance SeparableTextContainer Run where
     splitTextAt8 n r =
         ( r { runText = t1 }
         , r { runText = t2, runOffsetInSpan = runOffsetInSpan r + l1 }

@@ 1,5 1,6 @@
 module Data.Text.ParagraphLayout.TextContainer
-    (TextContainer
+    (SeparableTextContainer
+    ,TextContainer
     ,getText
     ,splitTextAt8
     ,splitTextsAt8


@@ 9,13 10,13 @@ where
 import Data.Text (Text)
 import Data.Text.Foreign (I8, lengthWord8)
 
+-- | Class of data types containing `Text` that can be accessed.
 class TextContainer a where
-
-    -- | Unwrap text from the container.
     getText :: a -> Text
 
-    -- | Split a text container at the given number of `Word8` units
-    -- from its beginning.
+-- | Class of data types containing `Text` that can be split at a given number
+-- of `Word8` units from the start of the text.
+class TextContainer a => SeparableTextContainer a where
     splitTextAt8 :: I8 -> a -> (a, a)
     splitTextAt8 _ _ = error "container cannot be split"
 


@@ 25,13 26,13 @@ class TextContainer a where
 --
 -- If @n@ falls on a container boundary, the total number of output containers
 -- will equal the number of input containers; otherwise, it will be one larger.
-splitTextsAt8 :: TextContainer a => I8 -> [a] -> ([a], [a])
+splitTextsAt8 :: SeparableTextContainer a => I8 -> [a] -> ([a], [a])
 splitTextsAt8 n rs = (pre, post)
     where
         pre = reverse rpre
         (rpre, post) = splitTextsAt8' n [] rs
 
-splitTextsAt8' :: TextContainer a => I8 -> [a] -> [a] -> ([a], [a])
+splitTextsAt8' :: SeparableTextContainer a => I8 -> [a] -> [a] -> ([a], [a])
 splitTextsAt8' _ rpre [] = (rpre, [])
 splitTextsAt8' n rpre (r:rs)
     | n <= 0 = (rpre, r:rs)