Lua: add Version type to simplify comparisons

Version specifiers like `PANDOC_VERSION` and `PANDOC_API_VERSION` are
turned into `Version` objects. The objects simplify version-appropriate
comparisons while maintaining backward-compatibility.

A function `pandoc.types.Version` is added as part of the newly
introduced module `pandoc.types`, allowing users to create version
objects in scripts.

2 files changed, 30 insertions, 0 deletions

diff --git a/src/Text/Pandoc/Lua/Module/Types.hs b/src/Text/Pandoc/Lua/Module/Types.hs
new file mode 100644
index 000000000..641bde7d6
--- /dev/null
+++ b/src/Text/Pandoc/Lua/Module/Types.hs
@@ -0,0 +1,28 @@
+{- |
+   Module      : Text.Pandoc.Lua.Module.Types
+   Copyright   : © 2019 Albert Krewinkel
+   License     : GNU GPL, version 2 or above
+
+   Maintainer  : Albert Krewinkel <tarleb+pandoc@moltkeplatz.de>
+   Stability   : alpha
+
+Pandoc data type constructors.
+-}
+module Text.Pandoc.Lua.Module.Types
+  ( pushModule
+  ) where
+
+import Prelude
+import Data.Version (Version)
+import Foreign.Lua (Lua, NumResults)
+import Text.Pandoc.Lua.Marshaling.Version ()
+import Text.Pandoc.Lua.Util (addFunction)
+
+import qualified Foreign.Lua as Lua
+
+-- | Push the pandoc.system module on the Lua stack.
+pushModule :: Lua NumResults
+pushModule = do
+  Lua.newtable
+  addFunction "Version" (return :: Version -> Lua Version)
+  return 1
diff --git a/src/Text/Pandoc/Lua/Module/Utils.hs b/src/Text/Pandoc/Lua/Module/Utils.hs
index 7f201a4b2..21e3f5674 100644
--- a/src/Text/Pandoc/Lua/Module/Utils.hs
+++ b/src/Text/Pandoc/Lua/Module/Utils.hs
@@ -17,6 +17,7 @@ import Prelude
 import Control.Applicative ((<|>))
 import Data.Char (toLower)
 import Data.Default (def)
+import Data.Version (Version)
 import Foreign.Lua (Peekable, Lua, NumResults)
 import Text.Pandoc.Class (runIO, setUserDataDir)
 import Text.Pandoc.Definition ( Pandoc, Meta, MetaValue (..), Block, Inline
@@ -43,6 +44,7 @@ pushModule mbDatadir = do
   addFunction "sha1" sha1
   addFunction "stringify" stringify
   addFunction "to_roman_numeral" toRomanNumeral
+  addFunction "Version" (return :: Version -> Lua Version)
   return 1
 
 -- | Squashes a list of blocks into inlines.