Manual merge of a patch from Duncan Coutts that removes the dependency on mtl

4 files changed, 14 insertions, 6 deletions

diff --git a/src/Haddock/Interface.hs b/src/Haddock/Interface.hs
index 4b178bf4..5f40422e 100644
--- a/src/Haddock/Interface.hs
+++ b/src/Haddock/Interface.hs
@@ -24,7 +24,6 @@ import Haddock.GHC.Utils
 import qualified Data.Map as Map
 import Data.Map (Map)
 import Data.List
-import Control.Monad.Writer
 import Control.Monad
 
 import Name
diff --git a/src/Haddock/Interface/Create.hs b/src/Haddock/Interface/Create.hs
index 800f099e..24db83b9 100644
--- a/src/Haddock/Interface/Create.hs
+++ b/src/Haddock/Interface/Create.hs
@@ -19,7 +19,7 @@ import Data.List
 import Data.Maybe
 import Data.Char
 import Data.Ord
-import Control.Monad.Writer
+import Control.Monad
 
 import GHC
 import Outputable
diff --git a/src/Haddock/Interface/Rename.hs b/src/Haddock/Interface/Rename.hs
index 2c231960..81717716 100644
--- a/src/Haddock/Interface/Rename.hs
+++ b/src/Haddock/Interface/Rename.hs
@@ -26,7 +26,6 @@ import Prelude hiding (mapM)
 import Data.Traversable (mapM)
 import Control.Arrow
 import Control.Monad hiding (mapM)
-import Control.Monad.Writer hiding (mapM)
 
 
 renameInterface :: LinkEnv -> Interface -> ErrMsgM Interface
diff --git a/src/Haddock/Types.hs b/src/Haddock/Types.hs
index 6143ae02..f1e01459 100644
--- a/src/Haddock/Types.hs
+++ b/src/Haddock/Types.hs
@@ -10,7 +10,6 @@ module Haddock.Types where
 
 import Data.Map (Map)
 import qualified Data.Map as Map
-import Control.Monad.Writer
 
 import GHC hiding (NoLink)
 import Outputable
@@ -203,7 +202,18 @@ data DocMarkup id a = Markup {
 }
 
 
--- A monad which collects error messages
+-- A monad which collects error messages, locally defined to avoid a dep on mtl
 
 type ErrMsg = String
-type ErrMsgM a = Writer [ErrMsg] a
+
+newtype ErrMsgM a = Writer { runWriter :: (a, [ErrMsg]) }
+
+instance Monad ErrMsgM where
+        return a = Writer (a, [])
+        m >>= k  = Writer $ let
+                (a, w)  = runWriter m
+                (b, w') = runWriter (k a)
+                in (b, w ++ w')
+
+tell :: [ErrMsg] -> ErrMsgM ()
+tell w = Writer ((), w)