Add variants of pandoc renderer and compiler for items

Add renderPandocItemWithTransformM and pandocItemCompilerWithTransformM,
which work like the respective functions without the `item' infix, but
the transformation function is an Item Pandoc -> Item Pandoc instead of
just a Pandoc -> Pandoc. This allows one to more seamlessly compose
functions that do require the extra information that an item provides,
like bibliographic transformations.

lib/Hakyll/Web/Pandoc.hs

@@ -10,12 +10,14 @@ module Hakyll.Web.Pandoc
     , renderPandocWith
     , renderPandocWithTransform
     , renderPandocWithTransformM
+    , renderPandocItemWithTransformM
 
       -- * Derived compilers
     , pandocCompiler
     , pandocCompilerWith
     , pandocCompilerWithTransform
     , pandocCompilerWithTransformM
+    , pandocItemCompilerWithTransformM
 
       -- * Default options
     , defaultHakyllReaderOptions
@@ -132,6 +134,21 @@ renderPandocWithTransformM ropt wopt f i =
     writePandocWith wopt <$> (traverse f =<< readPandocWith ropt i)
 
 
+--------------------------------------------------------------------------------
+-- | Like 'renderPandocWithTransformM', but work on an 'Item' 'Pandoc' instead
+-- of just a 'Pandoc'. This allows for more seamless composition of functions
+-- that require the extra information that an 'Item' provides, like
+-- bibliographic transformations with
+-- 'Hakyll.Web.Pandoc.Biblio.processPandocBiblio'.
+renderPandocItemWithTransformM
+  :: ReaderOptions -> WriterOptions
+  -> (Item Pandoc -> Compiler (Item Pandoc))
+  -> Item String
+  -> Compiler (Item String)
+renderPandocItemWithTransformM ropt wopt f i =
+    writePandocWith wopt <$> (f =<< readPandocWith ropt i)
+
+
 --------------------------------------------------------------------------------
 -- | Read a page render using pandoc
 pandocCompiler :: Compiler (Item String)
@@ -170,6 +187,20 @@ pandocCompilerWithTransformM ropt wopt f =
     getResourceBody >>= renderPandocWithTransformM ropt wopt f
 
 
+--------------------------------------------------------------------------------
+-- | Like 'pandocCompilerWithTransformM', but work on an 'Item' 'Pandoc'
+-- instead of just a 'Pandoc'. This allows for more seamless composition of
+-- functions that require the extra information that an 'Item' provides, like
+-- bibliographic transformations with
+-- 'Hakyll.Web.Pandoc.Biblio.processPandocBiblio'.
+pandocItemCompilerWithTransformM
+  :: ReaderOptions -> WriterOptions
+  -> (Item Pandoc -> Compiler (Item Pandoc))
+  -> Compiler (Item String)
+pandocItemCompilerWithTransformM ropt wopt f =
+    getResourceBody >>= renderPandocItemWithTransformM ropt wopt f
+
+
 --------------------------------------------------------------------------------
 -- | The default reader options for pandoc parsing in hakyll
 defaultHakyllReaderOptions :: ReaderOptions