3 files changed, 58 insertions, 12 deletions
diff --git a/src/Blessings.hs b/src/Blessings.hs
index 26a0666..559db3e 100644
--- a/src/Blessings.hs
+++ b/src/Blessings.hs
@@ -47,13 +47,16 @@ instance Functor Blessings where
 instance Semigroup (Blessings a) where
     t <> Empty = t
     Empty <> t = t
-    Append t1 t2 <> Append t3 t4 = t1 <> t2 <> t3 <> t4
-    Append t1 t2 <> t3 = t1 <> t2 <> t3
+    Append t1 t2 <> t3 = Append t1 (t2 <> t3)
     t1 <> t2 = Append t1 t2
 
 
 instance Monoid (Blessings a) where
     mempty = Empty
+    mconcat = \case
+      x:[] -> x
+      x:xs -> Append x $ mconcat xs
+      [] -> Empty
 
 
 instance IsString a => IsString (Blessings a) where
@@ -151,8 +154,8 @@ instance IsPm Underline where
         rec xs = case filter (`elem` ([4,24] :: [Word8])) xs of
             [] -> Nothing
             xs' -> case last xs' of
-                1 -> Just Underline
-                22 -> Just NoUnderline
+                4 -> Just Underline
+                24 -> Just NoUnderline
                 _ -> error "filter broken in fromPm :: Pm -> Maybe Underline"
 
 
@@ -273,10 +276,16 @@ instance Blessable a => Blessable (Blessings a) where
 
   drop n = \case
       Append t1 t2 ->
-          case compare n (Bless.length t1) of
-              LT -> Bless.drop n t1 <> t2
-              EQ -> t2
-              GT -> Bless.drop (n - Bless.length t1) t2
+          let
+            n1 = Bless.length (Bless.take n t1)
+            n2 = n - n1
+            t1' = Bless.drop n1 t1
+            t2' = Bless.drop n2 t2
+            isEmpty = (==0) . Bless.length . Bless.take 1
+          in
+            if n1 /= n || isEmpty t1'
+              then t2'
+              else Append t1' t2'
       Plain s ->
           Plain (Bless.drop n s)
       SGR pm t ->
@@ -286,10 +295,13 @@ instance Blessable a => Blessable (Blessings a) where
 
   take n = \case
       Append t1 t2 ->
-          case compare n (Bless.length t1) of
-              LT -> Bless.take n t1
-              EQ -> t1
-              GT -> t1 <> Bless.take (n - Bless.length t1) t2
+          let
+            t1' = Bless.take n t1
+            n' = n - Bless.length t1'
+          in
+            if n' > 0
+              then t1' <> Bless.take n' t2
+              else t1'
       Plain s ->
           Plain (Bless.take n s)
       SGR pm t ->
diff --git a/src/Blessings/ByteString.hs b/src/Blessings/ByteString.hs
new file mode 100644
index 0000000..d914818
--- /dev/null
+++ b/src/Blessings/ByteString.hs
@@ -0,0 +1,17 @@
+{-# OPTIONS_GHC -fno-warn-orphans #-}
+
+module Blessings.ByteString
+    ( module Blessings
+    ) where
+
+import Blessings
+import Blessings.Internal
+import qualified Data.ByteString.Char8 as B
+
+
+instance Blessable B.ByteString where
+  length = B.length
+  drop = B.drop
+  take = B.take
+  intercalate = B.intercalate
+  fromWord8 = B.pack . show
diff --git a/src/Blessings/ByteString/Lazy.hs b/src/Blessings/ByteString/Lazy.hs
new file mode 100644
index 0000000..a32f29b
--- /dev/null
+++ b/src/Blessings/ByteString/Lazy.hs
@@ -0,0 +1,17 @@
+{-# OPTIONS_GHC -fno-warn-orphans #-}
+
+module Blessings.ByteString.Lazy
+    ( module Blessings
+    ) where
+
+import Blessings
+import Blessings.Internal
+import qualified Data.ByteString.Lazy.Char8 as L
+
+
+instance Blessable L.ByteString where
+  length = fromIntegral . L.length
+  drop = L.drop . fromIntegral
+  take = L.take . fromIntegral
+  intercalate = L.intercalate
+  fromWord8 = L.pack . show