Factorize stack-editing functions in Annotation

lib/Text/TEIWA/Annotation.hs

@@ -32,12 +32,12 @@ data Annotation = Token Text | Annotations [Node] deriving Show
 attribute :: (Text, Text) -> Text
 attribute (k, v) = Text.concat [" ", k, "=\"", v, "\""]
 
-openTag :: Tag -> String
-openTag (Tag {name, annotated}) =
+openTag :: Tag -> Editor m
+openTag (Tag {name, annotated}) = tell . Text.pack $
   printf "<%s%s>" name . Text.concat $ attribute <$> annotated
 
-closeTag :: Tag -> String
-closeTag = printf "</%s>" . name
+closeTag :: Tag -> Editor m
+closeTag = tell . Text.pack $ printf "</%s>" . name
 
 data EditorState = EditorState {
       input :: Text
@@ -45,15 +45,13 @@ data EditorState = EditorState {
   }
 type Editor m = RWST Config Text EditorState m ()
 
-enter :: Monad m => Tag -> Editor m
-enter t = modify $
-  \editorState -> editorState {tagStack = t:tagStack editorState}
+editStack :: MonadState EditorState m => ([Tag] -> (a, [Tag])) -> m a
+editStack f = state $ \editorState ->
+  let (output, newTagStack) = f $ tagStack editorState in
+  (output, editorState {tagStack = newTagStack})
 
 flushTags :: Monad m => Editor m
-flushTags = do
-  tags <- gets tagStack
-  modify $ \editorState -> editorState {tagStack = []}
-  mapM_ (tell . Text.pack . openTag) tags
+flushTags = editStack (\stack -> (stack, [])) >>= mapM_ openTag
 
 forget :: Monad m => Int64 -> Editor m
 forget count = modify $
@@ -61,7 +59,7 @@ forget count = modify $
 
 annotateNode :: MonadError Error m => Node -> Editor m
 annotateNode (Node {tag, inside}) =
-  enter tag *> annotator inside *> tell (Text.pack $ closeTag tag)
+  editStack (\s -> ((), tag:s)) *> annotator inside *> closeTag tag
 
 annotator :: MonadError Error m => Annotation -> Editor m
 annotator (Token t) = gets (Text.breakOn t . input) >>= wrap