1 files changed, 13 insertions, 20 deletions
diff --git a/src/Text/Pandoc/Lua/Util.hs b/src/Text/Pandoc/Lua/Util.hs
index 2958bd734..a3af155c9 100644
--- a/src/Text/Pandoc/Lua/Util.hs
+++ b/src/Text/Pandoc/Lua/Util.hs
@@ -1,6 +1,6 @@
 {-
-Copyright © 2012-2017 John MacFarlane <jgm@berkeley.edu>
-            2017 Albert Krewinkel <tarleb+pandoc@moltkeplatz.de>
+Copyright © 2012-2018 John MacFarlane <jgm@berkeley.edu>
+            2017-2018 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
@@ -19,8 +19,8 @@ Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 {-# LANGUAGE FlexibleInstances #-}
 {- |
    Module      : Text.Pandoc.Lua.Util
-   Copyright   : © 2012–2017 John MacFarlane,
-                 © 2017 Albert Krewinkel
+   Copyright   : © 2012–2018 John MacFarlane,
+                 © 2017-2018 Albert Krewinkel
    License     : GNU GPL, version 2 or above
 
    Maintainer  : Albert Krewinkel <tarleb+pandoc@moltkeplatz.de>
@@ -36,9 +36,9 @@ module Text.Pandoc.Lua.Util
   , getRawInt
   , setRawInt
   , addRawInt
+  , typeCheck
   , raiseError
   , popValue
-  , OrNil (..)
   , PushViaCall
   , pushViaCall
   , pushViaConstructor
@@ -101,6 +101,14 @@ setRawInt idx key value = do
 addRawInt :: ToLuaStack a => Int -> a -> Lua ()
 addRawInt = setRawInt (-1)
 
+typeCheck :: StackIndex -> Lua.Type -> Lua ()
+typeCheck idx expected = do
+  actual <- Lua.ltype idx
+  when (actual /= expected) $ do
+    expName <- Lua.typename expected
+    actName <- Lua.typename actual
+    Lua.throwLuaError $ "expected " ++ expName ++ " but got " ++ actName ++ "."
+
 raiseError :: ToLuaStack a => a -> Lua NumResults
 raiseError e = do
   Lua.push e
@@ -115,21 +123,6 @@ popValue = do
     Left err -> Lua.throwLuaError err
     Right x -> return x
 
--- | Newtype wrapper intended to be used for optional Lua values. Nesting this
--- type is strongly discouraged and will likely lead to a wrong result.
-newtype OrNil a = OrNil { toMaybe :: Maybe a }
-
-instance FromLuaStack a => FromLuaStack (OrNil a) where
-  peek idx = do
-    noValue <- Lua.isnoneornil idx
-    if noValue
-      then return (OrNil Nothing)
-      else OrNil . Just <$> Lua.peek idx
-
-instance ToLuaStack a => ToLuaStack (OrNil a) where
-  push (OrNil Nothing)  = Lua.pushnil
-  push (OrNil (Just x)) = Lua.push x
-
 -- | Helper class for pushing a single value to the stack via a lua function.
 -- See @pushViaCall@.
 class PushViaCall a where