1 files changed, 17 insertions, 4 deletions
diff --git a/haddock-library/src/Documentation/Haddock/Doc.hs b/haddock-library/src/Documentation/Haddock/Doc.hs
index fe8cf99b..66bd1c97 100644
--- a/haddock-library/src/Documentation/Haddock/Doc.hs
+++ b/haddock-library/src/Documentation/Haddock/Doc.hs
@@ -1,15 +1,20 @@
 {-# OPTIONS_GHC -fno-warn-orphans #-}
 module Documentation.Haddock.Doc (docParagraph, docAppend,
                                   docConcat, metaDocConcat,
-                                  metaDocAppend, emptyMetaDoc) where
+                                  metaDocAppend, emptyMetaDoc,
+                                  metaAppend, metaConcat) where
 
-import Data.Monoid (mempty, (<>))
+import Control.Applicative ((<|>), empty)
 import Documentation.Haddock.Types
 import Data.Char (isSpace)
 
 docConcat :: [DocH mod id] -> DocH mod id
 docConcat = foldr docAppend DocEmpty
 
+-- | Concat using 'metaAppend'.
+metaConcat :: [Meta] -> Meta
+metaConcat = foldr metaAppend emptyMeta
+
 -- | Like 'docConcat' but also joins the 'Meta' info.
 metaDocConcat :: [MetaDoc mod id] -> MetaDoc mod id
 metaDocConcat = foldr metaDocAppend emptyMetaDoc
@@ -20,10 +25,18 @@ metaDocConcat = foldr metaDocAppend emptyMetaDoc
 metaDocAppend :: MetaDoc mod id -> MetaDoc mod id -> MetaDoc mod id
 metaDocAppend (MetaDoc { _meta = m, _doc = d })
               (MetaDoc { _meta = m', _doc = d' }) =
-  MetaDoc { _meta = m' <> m, _doc = d `docAppend` d' }
+  MetaDoc { _meta = m' `metaAppend` m, _doc = d `docAppend` d' }
+
+-- | This is not a monoidal append, it uses '<|>' for the '_version'.
+metaAppend :: Meta -> Meta -> Meta
+metaAppend (Meta { _version = v }) (Meta { _version = v' }) =
+  Meta { _version = v <|> v' }
 
 emptyMetaDoc :: MetaDoc mod id
-emptyMetaDoc = MetaDoc { _meta = mempty, _doc = DocEmpty }
+emptyMetaDoc = MetaDoc { _meta = emptyMeta, _doc = DocEmpty }
+
+emptyMeta :: Meta
+emptyMeta = Meta { _version = empty }
 
 docAppend :: DocH mod id -> DocH mod id -> DocH mod id
 docAppend (DocDefList ds1) (DocDefList ds2) = DocDefList (ds1++ds2)