Avoid repeating StackValue instances definitions

The lua filters and custom lua writer system defined very similar
StackValue instances for strings and tuples.  These instance definitions
are extracted to a separate module to enable sharing.

4 files changed, 165 insertions, 156 deletions

diff --git a/src/Text/Pandoc/Lua/SharedInstances.hs b/src/Text/Pandoc/Lua/SharedInstances.hs
new file mode 100644
index 000000000..02438b93b
--- /dev/null
+++ b/src/Text/Pandoc/Lua/SharedInstances.hs
@@ -0,0 +1,106 @@
+{-
+Copyright © 2012-2016 John MacFarlane <jgm@berkeley.edu>
+            2017 Albert Krewinkel <tarleb+pandoc@moltkeplatz.de>
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+-}
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE LambdaCase #-}
+#if !MIN_VERSION_base(4,8,0)
+{-# LANGUAGE OverlappingInstances #-}
+#endif
+{-# OPTIONS_GHC -fno-warn-orphans #-}
+{- |
+   Module      : Text.Pandoc.Lua.SharedInstances
+   Copyright   : © 2012–2016 John MacFarlane,
+                 © 2017 Albert Krewinkel
+   License     : GNU GPL, version 2 or above
+
+   Maintainer  : Albert Krewinkel <tarleb+pandoc@moltkeplatz.de>
+   Stability   : alpha
+
+Shared StackValue instances for pandoc and generic types.
+-}
+module Text.Pandoc.Lua.SharedInstances () where
+
+import Scripting.Lua ( LTYPE(..), StackValue(..), newtable )
+import Text.Pandoc.Lua.Util ( addRawInt, addValue, getRawInt, keyValuePairs )
+
+import qualified Data.Map as M
+import qualified Text.Pandoc.UTF8 as UTF8
+
+#if MIN_VERSION_base(4,8,0)
+instance {-# OVERLAPS #-} StackValue [Char] where
+#else
+instance StackValue [Char] where
+#endif
+  push lua cs = push lua (UTF8.fromString cs)
+  peek lua i = fmap UTF8.toString <$> peek lua i
+  valuetype _ = TSTRING
+
+instance (StackValue a, StackValue b) => StackValue (a, b) where
+  push lua (a, b) = do
+    newtable lua
+    addRawInt lua 1 a
+    addRawInt lua 2 b
+  peek lua idx = do
+    a <- getRawInt lua idx 1
+    b <- getRawInt lua idx 2
+    return $ (,) <$> a <*> b
+  valuetype _ = TTABLE
+
+instance (StackValue a, StackValue b, StackValue c) =>
+         StackValue (a, b, c)
+ where
+  push lua (a, b, c) = do
+    newtable lua
+    addRawInt lua 1 a
+    addRawInt lua 2 b
+    addRawInt lua 3 c
+  peek lua idx = do
+    a <- getRawInt lua idx 1
+    b <- getRawInt lua idx 2
+    c <- getRawInt lua idx 3
+    return $ (,,) <$> a <*> b <*> c
+  valuetype _ = TTABLE
+
+instance (StackValue a, StackValue b, StackValue c,
+          StackValue d, StackValue e) =>
+         StackValue (a, b, c, d, e)
+ where
+  push lua (a, b, c, d, e) = do
+    newtable lua
+    addRawInt lua 1 a
+    addRawInt lua 2 b
+    addRawInt lua 3 c
+    addRawInt lua 4 d
+    addRawInt lua 5 e
+  peek lua idx = do
+    a <- getRawInt lua idx 1
+    b <- getRawInt lua idx 2
+    c <- getRawInt lua idx 3
+    d <- getRawInt lua idx 4
+    e <- getRawInt lua idx 5
+    return $ (,,,,) <$> a <*> b <*> c <*> d <*> e
+  valuetype _ = TTABLE
+
+instance (Ord a, StackValue a, StackValue b) =>
+         StackValue (M.Map a b) where
+  push lua m = do
+    newtable lua
+    mapM_ (uncurry $ addValue lua) $ M.toList m
+  peek lua idx = fmap M.fromList <$> keyValuePairs lua idx
+  valuetype _ = TTABLE
diff --git a/src/Text/Pandoc/Lua/StackInstances.hs b/src/Text/Pandoc/Lua/StackInstances.hs
index 8e26ece55..8af7f78c0 100644
--- a/src/Text/Pandoc/Lua/StackInstances.hs
+++ b/src/Text/Pandoc/Lua/StackInstances.hs
@@ -16,12 +16,8 @@ You should have received a copy of the GNU General Public License
 along with this program; if not, write to the Free Software
 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 -}
-{-# LANGUAGE CPP #-}
 {-# LANGUAGE FlexibleInstances #-}
 {-# LANGUAGE LambdaCase #-}
-#if !MIN_VERSION_base(4,8,0)
-{-# LANGUAGE OverlappingInstances #-}
-#endif
 {-# OPTIONS_GHC -fno-warn-orphans #-}
 {- |
    Module      : Text.Pandoc.Lua.StackInstances
@@ -38,15 +34,10 @@ module Text.Pandoc.Lua.StackInstances () where
 
 import Control.Applicative ( (<|>) )
 import Scripting.Lua
-  ( LTYPE(..), LuaState, StackValue(..)
-  , call, getglobal2, ltype, newtable, next, objlen, pop, pushnil
-  )
+  ( LTYPE(..), LuaState, StackValue(..), getglobal2, ltype, newtable, objlen )
 import Text.Pandoc.Definition
-import Text.Pandoc.Lua.Util
-  ( adjustIndexBy, addValue, getTable, addRawInt, getRawInt )
-
-import qualified Data.Map as M
-import qualified Text.Pandoc.UTF8 as UTF8
+import Text.Pandoc.Lua.SharedInstances ()
+import Text.Pandoc.Lua.Util ( addValue, getTable, pushViaConstructor )
 
 instance StackValue Pandoc where
   push lua (Pandoc meta blocks) = do
@@ -261,119 +252,6 @@ instance StackValue QuoteType where
       _ -> return Nothing
   valuetype _ = TTABLE
 
-#if MIN_VERSION_base(4,8,0)
-instance {-# OVERLAPS #-} StackValue [Char] where
-#else
-instance StackValue [Char] where
-#endif
-  push lua cs = push lua (UTF8.fromString cs)
-  peek lua i = fmap UTF8.toString <$> peek lua i
-  valuetype _ = TSTRING
-
-instance (StackValue a, StackValue b) => StackValue (a, b) where
-  push lua (a, b) = do
-    newtable lua
-    addRawInt lua 1 a
-    addRawInt lua 2 b
-  peek lua idx = do
-    a <- getRawInt lua idx 1
-    b <- getRawInt lua idx 2
-    return $ (,) <$> a <*> b
-  valuetype _ = TTABLE
-
-instance (StackValue a, StackValue b, StackValue c) =>
-         StackValue (a, b, c)
- where
-  push lua (a, b, c) = do
-    newtable lua
-    addRawInt lua 1 a
-    addRawInt lua 2 b
-    addRawInt lua 3 c
-  peek lua idx = do
-    a <- getRawInt lua idx 1
-    b <- getRawInt lua idx 2
-    c <- getRawInt lua idx 3
-    return $ (,,) <$> a <*> b <*> c
-  valuetype _ = TTABLE
-
-instance (StackValue a, StackValue b, StackValue c,
-          StackValue d, StackValue e) =>
-         StackValue (a, b, c, d, e)
- where
-  push lua (a, b, c, d, e) = do
-    newtable lua
-    addRawInt lua 1 a
-    addRawInt lua 2 b
-    addRawInt lua 3 c
-    addRawInt lua 4 d
-    addRawInt lua 5 e
-  peek lua idx = do
-    a <- getRawInt lua idx 1
-    b <- getRawInt lua idx 2
-    c <- getRawInt lua idx 3
-    d <- getRawInt lua idx 4
-    e <- getRawInt lua idx 5
-    return $ (,,,,) <$> a <*> b <*> c <*> d <*> e
-  valuetype _ = TTABLE
-
-instance (Ord a, StackValue a, StackValue b) =>
-         StackValue (M.Map a b) where
-  push lua m = do
-    newtable lua
-    mapM_ (uncurry $ addValue lua) $ M.toList m
-  peek lua idx = fmap M.fromList <$> keyValuePairs lua idx
-  valuetype _ = TTABLE
-
--- | Try reading the value under the given index as a list of key-value pairs.
-keyValuePairs :: (StackValue a, StackValue b)
-         => LuaState -> Int -> IO (Maybe [(a, b)])
-keyValuePairs lua idx = do
-  pushnil lua
-  sequence <$> remainingPairs
- where
-  remainingPairs = do
-    res <- nextPair
-    case res of
-      Nothing -> return []
-      Just a  -> (a:) <$> remainingPairs
-  nextPair :: (StackValue a, StackValue b) => IO (Maybe (Maybe (a,b)))
-  nextPair = do
-    hasNext <- next lua (idx `adjustIndexBy` 1)
-    if hasNext
-      then do
-        val <- peek lua (-1)
-        key <- peek lua (-2)
-        pop lua 1 -- removes the value, keeps the key
-        return $ Just <$> ((,) <$> key <*> val)
-      else do
-        return Nothing
-
-
--- | Helper class for pushing a single value to the stack via a lua function.
--- See @pushViaCall@.
-class PushViaCall a where
-  pushViaCall' :: LuaState -> String -> IO () -> Int -> a
-
-instance PushViaCall (IO ()) where
-  pushViaCall' lua fn pushArgs num = do
-    getglobal2 lua fn
-    pushArgs
-    call lua num 1
-
-instance (StackValue a, PushViaCall b) => PushViaCall (a -> b) where
-  pushViaCall' lua fn pushArgs num x =
-    pushViaCall' lua fn (pushArgs *> push lua x) (num + 1)
-
--- | Push an value to the stack via a lua function. The lua function is called
--- with all arguments that are passed to this function and is expected to return
--- a single value.
-pushViaCall :: PushViaCall a => LuaState -> String -> a
-pushViaCall lua fn = pushViaCall' lua fn (return ()) 0
-
--- | Call a pandoc element constructor within lua, passing all given arguments.
-pushViaConstructor :: PushViaCall a => LuaState -> String -> a
-pushViaConstructor lua pandocFn = pushViaCall lua ("pandoc." ++ pandocFn)
-
 -- | Return the value at the given index as inline if possible.
 peekInline :: LuaState -> Int -> IO (Maybe Inline)
 peekInline lua idx = do
diff --git a/src/Text/Pandoc/Lua/Util.hs b/src/Text/Pandoc/Lua/Util.hs
index 9c5625c3c..f0b87c231 100644
--- a/src/Text/Pandoc/Lua/Util.hs
+++ b/src/Text/Pandoc/Lua/Util.hs
@@ -16,6 +16,7 @@ You should have received a copy of the GNU General Public License
 along with this program; if not, write to the Free Software
 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 -}
+{-# LANGUAGE FlexibleInstances #-}
 {- |
    Module      : Text.Pandoc.Lua.Util
    Copyright   : © 2012–2016 John MacFarlane,
@@ -35,11 +36,15 @@ module Text.Pandoc.Lua.Util
   , getRawInt
   , setRawInt
   , addRawInt
+  , keyValuePairs
+  , PushViaCall
+  , pushViaCall
+  , pushViaConstructor
   ) where
 
 import Scripting.Lua
   ( LuaState, StackValue(..)
-  , gettable, pop, rawgeti, rawseti, settable
+  , call, getglobal2, gettable, next, pop, pushnil, rawgeti, rawseti, settable
   )
 
 -- | Adjust the stack index, assuming that @n@ new elements have been pushed on
@@ -84,3 +89,52 @@ setRawInt lua idx key value = do
 -- | Set numeric key/value in table at the top of the stack.
 addRawInt :: StackValue a => LuaState -> Int -> a -> IO ()
 addRawInt lua = setRawInt lua (-1)
+
+-- | Try reading the table under the given index as a list of key-value pairs.
+keyValuePairs :: (StackValue a, StackValue b)
+              => LuaState -> Int -> IO (Maybe [(a, b)])
+keyValuePairs lua idx = do
+  pushnil lua
+  sequence <$> remainingPairs
+ where
+  remainingPairs = do
+    res <- nextPair
+    case res of
+      Nothing -> return []
+      Just a  -> (a:) <$> remainingPairs
+  nextPair :: (StackValue a, StackValue b) => IO (Maybe (Maybe (a,b)))
+  nextPair = do
+    hasNext <- next lua (idx `adjustIndexBy` 1)
+    if hasNext
+      then do
+        val <- peek lua (-1)
+        key <- peek lua (-2)
+        pop lua 1 -- removes the value, keeps the key
+        return $ Just <$> ((,) <$> key <*> val)
+      else do
+        return Nothing
+
+-- | Helper class for pushing a single value to the stack via a lua function.
+-- See @pushViaCall@.
+class PushViaCall a where
+  pushViaCall' :: LuaState -> String -> IO () -> Int -> a
+
+instance PushViaCall (IO ()) where
+  pushViaCall' lua fn pushArgs num = do
+    getglobal2 lua fn
+    pushArgs
+    call lua num 1
+
+instance (StackValue a, PushViaCall b) => PushViaCall (a -> b) where
+  pushViaCall' lua fn pushArgs num x =
+    pushViaCall' lua fn (pushArgs *> push lua x) (num + 1)
+
+-- | Push an value to the stack via a lua function. The lua function is called
+-- with all arguments that are passed to this function and is expected to return
+-- a single value.
+pushViaCall :: PushViaCall a => LuaState -> String -> a
+pushViaCall lua fn = pushViaCall' lua fn (return ()) 0
+
+-- | Call a pandoc element constructor within lua, passing all given arguments.
+pushViaConstructor :: PushViaCall a => LuaState -> String -> a
+pushViaConstructor lua pandocFn = pushViaCall lua ("pandoc." ++ pandocFn)
diff --git a/src/Text/Pandoc/Writers/Custom.hs b/src/Text/Pandoc/Writers/Custom.hs
index b06dd0c8a..ce90e4834 100644
--- a/src/Text/Pandoc/Writers/Custom.hs
+++ b/src/Text/Pandoc/Writers/Custom.hs
@@ -47,6 +47,7 @@ import Scripting.Lua (LuaState, StackValue, callfunc)
 import qualified Scripting.Lua as Lua
 import Text.Pandoc.Lua.Compat ( loadstring )
 import Text.Pandoc.Lua.Util ( addValue )
+import Text.Pandoc.Lua.SharedInstances ()
 import Text.Pandoc.Definition
 import Text.Pandoc.Options
 import Text.Pandoc.Templates
@@ -59,41 +60,11 @@ attrToMap (id',classes,keyvals) = M.fromList
     : ("class", unwords classes)
     : keyvals
 
-#if MIN_VERSION_base(4,8,0)
-instance {-# OVERLAPS #-} StackValue [Char] where
-#else
-instance StackValue [Char] where
-#endif
-  push lua cs = Lua.push lua (UTF8.fromString cs)
-  peek lua i = do
-                 res <- Lua.peek lua i
-                 return $ UTF8.toString `fmap` res
-  valuetype _ = Lua.TSTRING
-
 instance StackValue Format where
   push lua (Format f) = Lua.push lua (map toLower f)
   peek l n = fmap Format `fmap` Lua.peek l n
   valuetype _ = Lua.TSTRING
 
-instance (StackValue a, StackValue b) => StackValue (M.Map a b) where
-  push lua m = do
-    let xs = M.toList m
-    Lua.createtable lua (length xs + 1) 0
-    let addValue (k, v) = Lua.push lua k >> Lua.push lua v >>
-                          Lua.rawset lua (-3)
-    mapM_ addValue xs
-  peek _ _ = undefined -- not needed for our purposes
-  valuetype _ = Lua.TTABLE
-
-instance (StackValue a, StackValue b) => StackValue (a,b) where
-  push lua (k,v) = do
-    Lua.createtable lua 2 0
-    Lua.push lua k
-    Lua.push lua v
-    Lua.rawset lua (-3)
-  peek _ _ = undefined -- not needed for our purposes
-  valuetype _ = Lua.TTABLE
-
 #if MIN_VERSION_base(4,8,0)
 instance {-# OVERLAPS #-} StackValue [Inline] where
 #else