[FIX] bug in number of returned document (Right a <> Right b = Right a insead of Right (a <> b))

src/PUBMED.hs

@@ -24,6 +24,7 @@ import Data.Attoparsec.ByteString.Char8 (anyChar)
 import qualified Data.ByteString.Lazy as LBS
 import qualified Data.ByteString      as DB
 import qualified Data.Text as T
+import qualified Data.List as List
 
 -- | API main function
 getMetadataWith :: Text -> Maybe Limit -> IO (Either Text [PubMed])
@@ -56,11 +57,16 @@ type Limit = Integer
 
 runMultipleFPAR :: [Integer]
                 -> IO (Either Text [PubMed])
-runMultipleFPAR ids
-  | length ids < 300 = runSimpleFetchPubmedAbstractRequest ids
-  | otherwise = do
-      runSimpleFetchPubmedAbstractRequest (Prelude.take 300 ids)
-        <> runMultipleFPAR (drop 300 ids)
+runMultipleFPAR ids = List.foldl1' concat'
+                   <$> mapM runSimpleFetchPubmedAbstractRequest (by 300 ids)
+  where
+    by _ [] = []
+    by n ns = head' : ( by n tail')
+      where
+        (head',tail') = List.splitAt n ns
+
+    concat' (Right n) (Right m) = Right $ n <> m
+    concat' n m = n <> m
 
 runSimpleFetchPubmedAbstractRequest ::
   [Integer]