ALlow multiple comma-separated files for --defaults.

MANUAL.txt

@@ -356,11 +356,12 @@ header when requesting a document from a URL:
     `slidy`, `slideous`, or `s5` directory
     placed in this directory will override pandoc's normal defaults.
 
-`-d` *FILE*, `--defaults=`*FILE*
+`-d` *FILE*[,*FILE*,...], `--defaults=`*FILE*[,*FILE*,...]
 
 :   Specify a set of default option settings.  *FILE* is a YAML
     file whose fields correspond to command-line option
-    settings.  All options for document conversion, including input
+    settings.  (Multiple files may be specified, separated by
+    commas.) All options for document conversion, including input
     and output files, can be set using a defaults file.  The file will
     be searched for first in the working directory, and then in
     the `defaults` subdirectory of the user data directory

src/Text/Pandoc/App/CommandLineOptions.hs

@@ -64,6 +64,7 @@ import Data.Text (Text)
 import Text.DocTemplates (ToContext(toVal), Context(..))
 import qualified Text.Pandoc.UTF8 as UTF8
 import qualified Data.YAML as Y
+import Data.List.Split (splitWhen)
 
 parseOptions :: [OptDescr (Opt -> IO Opt)] -> Opt -> IO Opt
 parseOptions options' defaults = do
@@ -161,11 +162,8 @@ options =
 
     , Option "d" ["defaults"]
                  (ReqArg
-                  (\arg opt -> do
-                      let fp' = if null (takeExtension arg)
-                                   then addExtension arg "yaml"
-                                   else arg
-                      foldM applyDefaults opt [fp']
+                  (\arg opt ->
+                      foldM applyDefaults opt (splitWhen (==',') arg)
                   )
                   "FILE")
                 ""
@@ -982,7 +980,10 @@ splitField s =
 
 -- | Apply defaults from --defaults file.
 applyDefaults :: Opt -> FilePath -> IO Opt
-applyDefaults opt fp = runIOorExplode $ do
+applyDefaults opt filepath = runIOorExplode $ do
+  let fp = if null (takeExtension filepath)
+              then addExtension filepath "yaml"
+              else filepath
   setVerbosity $ optVerbosity opt
   dataDirs <- liftIO defaultUserDataDirs
   let fps = case optDataDir opt of