diff --git a/Language/Haskell/GhcMod.hs b/Language/Haskell/GhcMod.hs
index 5f201bb..379bba7 100644
--- a/Language/Haskell/GhcMod.hs
+++ b/Language/Haskell/GhcMod.hs
@@ -43,4 +43,5 @@ import Language.Haskell.GhcMod.Lang
 import Language.Haskell.GhcMod.Lint
 import Language.Haskell.GhcMod.List
 import Language.Haskell.GhcMod.PkgDoc
+import Language.Haskell.GhcMod.Rewrite
 import Language.Haskell.GhcMod.Types
diff --git a/Language/Haskell/GhcMod/Ghc.hs b/Language/Haskell/GhcMod/Ghc.hs
index 311053c..dd6caa8 100644
--- a/Language/Haskell/GhcMod/Ghc.hs
+++ b/Language/Haskell/GhcMod/Ghc.hs
@@ -26,3 +26,4 @@ import Language.Haskell.GhcMod.Find
 import Language.Haskell.GhcMod.GHCApi
 import Language.Haskell.GhcMod.Info
 import Language.Haskell.GhcMod.List
+import Language.Haskell.GhcMod.Rewrite
diff --git a/Language/Haskell/GhcMod/Info.hs b/Language/Haskell/GhcMod/Info.hs
index 9ca6616..14c338c 100644
--- a/Language/Haskell/GhcMod/Info.hs
+++ b/Language/Haskell/GhcMod/Info.hs
@@ -1,44 +1,24 @@
-{-# LANGUAGE TupleSections, FlexibleInstances, Rank2Types, LambdaCase #-}
-{-# OPTIONS_GHC -fno-warn-orphans #-}
-
 module Language.Haskell.GhcMod.Info (
     infoExpr
   , info
   , typeExpr
   , types
-  , splitVar
-  , splits
-  , fillSig
-  , sig
   ) where
 
 import Control.Applicative ((<$>))
-import CoreMonad (liftIO)
-import CoreUtils (exprType)
-import Data.Char (isSymbol)
 import Data.Function (on)
-import Data.Generics
-import Data.List (find, intercalate, sortBy)
-import Data.Maybe (catMaybes, fromMaybe)
-import Data.Ord as O
+import Data.List (sortBy)
+import Data.Maybe (catMaybes)
 import Exception (ghandle, SomeException(..))
-import GHC (Ghc, LHsBind, LHsExpr, LPat, Id, ParsedModule(..), TypecheckedModule(..), DynFlags, SrcSpan, Type, Located, ParsedSource, RenamedSource, TypecheckedSource, GenLocated(L))
+import GHC (Ghc, LHsBind, LHsExpr, LPat, Id, TypecheckedModule(..), SrcSpan, Type)
 import qualified GHC as G
-import GHC.SYB.Utils (Stage(..), everythingStaged, showData)
-import Language.Haskell.GhcMod.Doc (showPage, showOneLine, getStyle)
+import Language.Haskell.GhcMod.Doc (showPage)
 import Language.Haskell.GhcMod.GHCApi
-import Language.Haskell.GhcMod.Gap (HasType(..), setWarnTypedHoles, setDeferTypeErrors)
+import Language.Haskell.GhcMod.Gap (HasType(..))
 import qualified Language.Haskell.GhcMod.Gap as Gap
+import Language.Haskell.GhcMod.SrcUtils
 import Language.Haskell.GhcMod.Types
 import Language.Haskell.GhcMod.Convert
-import Outputable (PprStyle)
-import TcHsSyn (hsPatType)
-import qualified Type as Ty
-import qualified TyCon as Ty
-import qualified DataCon as Ty
-import qualified HsBinds as Ty
-import qualified Class as Ty
-import OccName (OccName, occName)
 
 ----------------------------------------------------------------
 
@@ -66,17 +46,6 @@ info opt file expr = convert opt <$> ghandle handler body
 
 ----------------------------------------------------------------
 
-instance HasType (LHsExpr Id) where
-    getType tcm e = do
-        hs_env <- G.getSession
-        mbe <- liftIO $ Gap.deSugar tcm e hs_env
-        return $ (G.getLoc e, ) <$> CoreUtils.exprType <$> mbe
-
-instance HasType (LPat Id) where
-    getType _ (G.L spn pat) = return $ Just (spn, hsPatType pat)
-
-----------------------------------------------------------------
-
 -- | Obtaining type of a target expression. (GHCi's type:)
 typeExpr :: Options
          -> Cradle
@@ -114,319 +83,3 @@ getSrcSpanType modSum lineNo colNo = do
     pts <- mapM (getType tcm) ps
     return $ catMaybes $ concat [ets, bts, pts]
 
-listifySpans :: Typeable a => TypecheckedSource -> (Int, Int) -> [Located a]
-listifySpans tcs lc = listifyStaged TypeChecker p tcs
-  where
-    p (L spn _) = G.isGoodSrcSpan spn && spn `G.spans` lc
-
-listifyParsedSpans :: Typeable a => ParsedSource -> (Int, Int) -> [Located a]
-listifyParsedSpans pcs lc = listifyStaged Parser p pcs
-  where
-    p (L spn _) = G.isGoodSrcSpan spn && spn `G.spans` lc
-
-listifyRenamedSpans :: Typeable a => RenamedSource -> (Int, Int) -> [Located a]
-listifyRenamedSpans pcs lc = listifyStaged Renamer p pcs
-  where
-    p (L spn _) = G.isGoodSrcSpan spn && spn `G.spans` lc
-
-listifyStaged :: Typeable r => Stage -> (r -> Bool) -> GenericQ [r]
-listifyStaged s p = everythingStaged s (++) [] ([] `mkQ` (\x -> [x | p x]))
-
-cmp :: SrcSpan -> SrcSpan -> Ordering
-cmp a b
-  | a `G.isSubspanOf` b = O.LT
-  | b `G.isSubspanOf` a = O.GT
-  | otherwise           = O.EQ
-
-toTup :: DynFlags -> PprStyle -> (SrcSpan, Type) -> ((Int,Int,Int,Int),String)
-toTup dflag style (spn, typ) = (fourInts spn, pretty dflag style typ)
-
-fourInts :: SrcSpan -> (Int,Int,Int,Int)
-fourInts = fromMaybe (0,0,0,0) . Gap.getSrcSpan
-
-pretty :: DynFlags -> PprStyle -> Type -> String
-pretty dflag style = showOneLine dflag style . Gap.typeForUser
-
-----------------------------------------------------------------
-
-inModuleContext :: FilePath -> (DynFlags -> PprStyle -> Ghc a) -> Ghc a
-inModuleContext file action =
-    withDynFlags (setWarnTypedHoles . setDeferTypeErrors . setNoWaringFlags) $ do
-    setTargetFiles [file]
-    Gap.withContext $ do
-        dflag <- G.getSessionDynFlags
-        style <- getStyle
-        action dflag style
-
-----------------------------------------------------------------
-
-data SplitInfo = SplitInfo G.Name (SrcSpan,Type) (SrcSpan, Type) [SrcSpan]
-
--- | Splitting a variable in a equation.
-splitVar :: Options
-         -> Cradle
-         -> FilePath     -- ^ A target file.
-         -> Int          -- ^ Line number.
-         -> Int          -- ^ Column number.
-         -> IO String
-splitVar opt cradle file lineNo colNo = withGHC' $ do
-    initializeFlagsWithCradle opt cradle
-    splits opt file lineNo colNo
-
--- | Splitting a variable in a equation.
-splits :: Options
-       -> FilePath     -- ^ A target file.
-       -> Int          -- ^ Line number.
-       -> Int          -- ^ Column number.
-       -> Ghc String
-splits opt file lineNo colNo = ghandle handler body
-  where
-    body = inModuleContext file $ \dflag style -> do
-        modSum <- Gap.fileModSummary file
-        splitInfo <- getSrcSpanTypeForSplit modSum lineNo colNo
-        case splitInfo of
-          Nothing -> return ""
-          Just (SplitInfo varName binding var@(_,varT) matches) -> do
-            return $ convert opt $ ( toTup dflag style binding
-                                   , toTup dflag style var
-                                   , (map fourInts matches)
-                                   , getTyCons dflag style varName varT)
-    handler (SomeException _) = return []
-
-getSrcSpanTypeForSplit :: G.ModSummary -> Int -> Int -> Ghc (Maybe SplitInfo)
-getSrcSpanTypeForSplit modSum lineNo colNo = do
-    p@ParsedModule{pm_parsed_source = pms} <- G.parseModule modSum
-    tcm@TypecheckedModule{tm_typechecked_source = tcs} <- G.typecheckModule p
-    let bs:_ = listifySpans tcs (lineNo, colNo) :: [LHsBind Id]
-        varPat  = find isPatternVar $ listifySpans tcs (lineNo, colNo) :: Maybe (LPat Id)
-        match:_ = listifyParsedSpans pms (lineNo, colNo) :: [G.LMatch G.RdrName (LHsExpr G.RdrName)]
-    case varPat of
-      Nothing  -> return Nothing
-      Just varPat' -> do
-        varT <- getType tcm varPat'  -- Finally we get the type of the var
-        bsT  <- getType tcm bs
-        case (varT, bsT) of
-          (Just varT', Just (_,bsT')) ->
-            let (L matchL (G.Match _ _ (G.GRHSs rhsLs _))) = match
-            in return $ Just (SplitInfo (getPatternVarName varPat') (matchL,bsT') varT' (map G.getLoc rhsLs) )
-          _ -> return Nothing
-
-isPatternVar :: LPat Id -> Bool
-isPatternVar (L _ (G.VarPat _)) = True
-isPatternVar _                  = False
-
-getPatternVarName :: LPat Id -> G.Name
-getPatternVarName (L _ (G.VarPat vName)) = G.getName vName
-getPatternVarName _                      = error "This should never happend"
-
-getTyCons :: DynFlags -> PprStyle -> G.Name -> G.Type ->  [String]
-getTyCons dflag style name ty | Just (tyCon, _) <- Ty.splitTyConApp_maybe ty =
-  let name' = showName dflag style name  -- Convert name to string
-  in getTyCon dflag style name' tyCon
-getTyCons dflag style name _ = [showName dflag style name]
-
--- Write cases for one type
-getTyCon :: DynFlags -> PprStyle -> String -> Ty.TyCon -> [String]
--- 1. Non-matcheable type constructors
-getTyCon _ _ name tyCon | isNotMatcheableTyCon tyCon = [name]
--- 2. Special cases
--- 2.1. Tuples
-getTyCon _ _ name tyCon | Ty.isTupleTyCon tyCon =
-  let [uniqueDataCon] = Ty.tyConDataCons tyCon
-      tupleArity = Ty.dataConSourceArity uniqueDataCon
-      -- Deal with both boxed and unboxed tuples
-      isUnboxed = Ty.isUnboxedTupleTyCon tyCon
-      startSign = if isUnboxed then "(#" else "("
-      endSign   = if isUnboxed then "#)" else ")"
-  in [ startSign ++ intercalate "," (map (\n -> name ++ show n) [1 .. tupleArity]) ++ endSign ]
--- 3. General case
-getTyCon dflag style name tyCon = map (getDataCon dflag style name) (Ty.tyConDataCons tyCon)
-
--- These type constructors should not be matched against
-isNotMatcheableTyCon :: Ty.TyCon -> Bool
-isNotMatcheableTyCon ty = Ty.isPrimTyCon ty  -- Primitive types, such as Int#
-                       || Ty.isFunTyCon ty   -- Function types
-
--- Write case for one constructor
-getDataCon :: DynFlags -> PprStyle -> String -> Ty.DataCon -> String
--- 1. Infix constructors
-getDataCon dflag style vName dcon | Ty.dataConIsInfix dcon =
-  let dName  = showName dflag style $ Ty.dataConName dcon
-  in case Ty.dataConSourceArity dcon of
-       0 -> dName
-       1 -> vName ++ dName
-       n -> if dName == ":" -- Special case for lists
-            then vName ++ ":" ++ vName ++ "s"
-            else newVar vName 1 ++ " " ++ dName ++ " " ++ newVars vName 2 (n-1)
--- 2. Non-record, non-infix syntax
-getDataCon dflag style vName dcon | [] <- Ty.dataConFieldLabels dcon =
-  let dName  = showName dflag style $ Ty.dataConName dcon
-  in if last dName == '#'  -- Special case for I#, C# and so on
-     then vName
-     else dName ++ " " ++ newVarsSpecialSingleton vName 1 (Ty.dataConSourceArity dcon)
--- 3. Records
-getDataCon dflag style vName dcon =
-  let dName = showName dflag style $ Ty.dataConName dcon
-      flds  = Ty.dataConFieldLabels dcon
-  in dName ++ " { " ++ showFieldNames dflag style vName flds ++ " }"
-
--- Create a new variable by adjoining a number
-newVar :: String -> Int -> String
-newVar v n = v ++ show n
-
--- Create a list of variables which start with the same prefix
-newVars :: String -> Int -> Int -> String
-newVars _ _ 0 = ""
-newVars v s 1 = newVar v s
-newVars v s m = newVar v s ++ " " ++ newVars v (s+1) (m-1)
-
--- Create a list of variables which start with the same prefix
--- Special case for a single variable, in which case no number is adjoint
-newVarsSpecialSingleton :: String -> Int -> Int -> String
-newVarsSpecialSingleton v _     1 = v
-newVarsSpecialSingleton v start n = newVars v start n
-
-showName :: DynFlags -> PprStyle -> G.Name -> String
-showName dflag style name = showOneLine dflag style $ Gap.nameForUser name
-
-showOccName :: DynFlags -> PprStyle -> OccName -> String
-showOccName dflag style name = showOneLine dflag style $ Gap.occNameForUser name
-
-showFieldNames :: DynFlags -> PprStyle -> String -> [G.Name] -> String
-showFieldNames _     _     _ []      = "" -- This should never happen
-showFieldNames dflag style v (x:xs) = let fName = showName dflag style x
-                                          fAcc  = fName ++ " = " ++ v ++ "_" ++ fName
-                                       in case xs of
-                                            [] -> fAcc
-                                            _  -> fAcc ++ ", " ++ showFieldNames dflag style v xs
-
-----------------------------------------------------------------
-
-data SigInfo = Signature SrcSpan [G.RdrName] (G.HsType G.RdrName)
-             | InstanceDecl SrcSpan G.Class
-
--- | Create a initial body from a signature.
-fillSig :: Options
-        -> Cradle
-        -> FilePath     -- ^ A target file.
-        -> Int          -- ^ Line number.
-        -> Int          -- ^ Column number.
-        -> IO String
-fillSig opt cradle file lineNo colNo = withGHC' $ do
-    initializeFlagsWithCradle opt cradle
-    sig opt file lineNo colNo
-
--- | Splitting a variable in a equation.
-sig :: Options
-       -> FilePath     -- ^ A target file.
-       -> Int          -- ^ Line number.
-       -> Int          -- ^ Column number.
-       -> Ghc String
-sig opt file lineNo colNo = ghandle handler body
-  where
-    body = inModuleContext file $ \dflag style -> do
-        modSum <- Gap.fileModSummary file
-        sigTy <- getSignature modSum lineNo colNo
-        case sigTy of
-          Nothing -> return ""
-          Just (Signature loc names ty) -> do
-            return $ convert opt $ ( fourInts loc
-                                   , map (initialFnBody dflag style ty) names
-                                   )
-          Just (InstanceDecl loc cls) -> do
-            return $ convert opt $ ( fourInts loc
-                                   , map (initialInstBody dflag style) (Ty.classMethods cls)
-                                   )
-            
-    handler (SomeException _) = return ""
-
-getSignature :: G.ModSummary -> Int -> Int -> Ghc (Maybe SigInfo)
-getSignature modSum lineNo colNo = do
-    p@ParsedModule{pm_parsed_source = ps} <- G.parseModule modSum
-    -- Look into the parse tree to find the signature
-    case listifyParsedSpans ps (lineNo, colNo) :: [G.LHsDecl G.RdrName] of
-      [L loc (G.SigD (Ty.TypeSig names (L _ ty)))] ->
-        -- We found a type signature
-        return $ Just $ Signature loc (map G.unLoc names) ty
-      [L _ (G.InstD _)] -> do
-        -- We found an instance declaration
-        TypecheckedModule{tm_renamed_source = Just tcs
-                         ,tm_checked_module_info = minfo} <- G.typecheckModule p
-        case listifyRenamedSpans tcs (lineNo, colNo) :: [G.LInstDecl G.Name] of
-          -- Instance declarations of sort 'instance F (G a)'
-          [L loc (G.ClsInstD (G.ClsInstDecl {G.cid_poly_ty =
-            (L _ (G.HsForAllTy _ _ _ (L _ (G.HsAppTy (L _ (G.HsTyVar clsName)) _))))}))] ->
-               obtainClassInfo minfo clsName loc
-          -- Instance declarations of sort 'instance F G' (no variables)
-          [L loc (G.ClsInstD (G.ClsInstDecl {G.cid_poly_ty =
-            (L _ (G.HsAppTy (L _ (G.HsTyVar clsName)) _))}))] ->
-               obtainClassInfo minfo clsName loc
-          _ -> return Nothing
-      _ -> return Nothing
-    where obtainClassInfo minfo clsName loc = do
-               tyThing <- G.modInfoLookupName minfo clsName
-               case tyThing of
-                 Just (Ty.ATyCon clsCon) -> 
-                   case G.tyConClass_maybe clsCon of
-                     Just cls -> return $ Just $ InstanceDecl loc cls
-                     Nothing  -> return Nothing
-                 _ -> return Nothing
-
--- A list of function arguments, and whether they are functions or normal arguments
--- is built from either a function signature or an instance signature
-data FnArg = FnArgFunction | FnArgNormal
-
-initialBody :: String -> [FnArg] -> String
-initialBody fname args =
-  case initialBodyArgs args infiniteVars infiniteFns of
-    []      -> fname
-    arglist -> if isSymbolName fname
-               then (head arglist) ++ " " ++ fname ++ " " ++ (intercalate " " (tail arglist))
-               else fname ++ " " ++ (intercalate " " arglist)
-  ++ " = _" ++ fname ++ "_body"
-
-initialBodyArgs :: [FnArg] -> [String] -> [String] -> [String]
-initialBodyArgs [] _ _ = []
-initialBodyArgs (FnArgFunction:xs) vs (f:fs) = f : initialBodyArgs xs vs fs
-initialBodyArgs (FnArgNormal:xs)   (v:vs) fs = v : initialBodyArgs xs vs fs
-initialBodyArgs _                  _      _  = error "This should never happen" -- Lists are infinite
-
--- Getting the initial body of function and instances differ
--- This is because for functions we only use the parsed file
--- (so the full file doesn't have to be type correct)
--- but for instances we need to get information about the class
-
-initialFnBody :: DynFlags -> PprStyle -> G.HsType G.RdrName -> G.RdrName -> String
-initialFnBody dflag style ty name = 
-  let fname = showOccName dflag style $ occName name  -- get function name
-      args  = \case (G.HsForAllTy _ _ _ (L _ iTy))  -> args iTy
-                    (G.HsParTy (L _ iTy))           -> args iTy
-                    (G.HsFunTy (L _ lTy) (L _ rTy)) -> (if fnarg lTy then FnArgFunction else FnArgNormal):args rTy
-                    _ -> []
-      fnarg = \case (G.HsForAllTy _ _ _ (L _ iTy)) -> fnarg iTy
-                    (G.HsParTy (L _ iTy))          -> fnarg iTy
-                    (G.HsFunTy _ _)                -> True
-                    _                              -> False
-   in initialBody fname (args ty)
-
-initialInstBody :: DynFlags -> PprStyle -> Id -> String
-initialInstBody dflag style method =
-  let fname = showOccName dflag style $ G.getOccName method  -- get function name
-      args  = \case ty | Just (lTy,rTy) <- Ty.splitFunTy_maybe ty ->
-                      case Ty.splitFunTy_maybe lTy of
-                        Just _  -> FnArgFunction:args rTy
-                        Nothing -> -- Drop the class predicates
-                                   if Ty.isPredTy lTy then args rTy else FnArgNormal:args rTy
-                    ty | Just (_,iTy) <- Ty.splitForAllTy_maybe ty -> args iTy
-                    _ -> []
-   in initialBody fname (args (Ty.dropForAlls $ G.idType method))
-
-infiniteVars, infiniteFns :: [String]
-infiniteVars = infiniteSupply ["x","y","z","t","u","v","w"]
-infiniteFns  = infiniteSupply ["f","g","h"]
-infiniteSupply :: [String] -> [String]
-infiniteSupply initialSupply = initialSupply ++ concatMap (\n -> map (\v -> v ++ show n) initialSupply) ([1 .. ] :: [Integer])
-
-isSymbolName :: String -> Bool
-isSymbolName (c:_) = c `elem` "!#$%&*+./<=>?@\\^|-~" || isSymbol c
-isSymbolName []    = error "This should never happen"
diff --git a/Language/Haskell/GhcMod/Rewrite.hs b/Language/Haskell/GhcMod/Rewrite.hs
new file mode 100644
index 0000000..db09f88
--- /dev/null
+++ b/Language/Haskell/GhcMod/Rewrite.hs
@@ -0,0 +1,301 @@
+{-# LANGUAGE LambdaCase #-}
+
+module Language.Haskell.GhcMod.Rewrite (
+    splitVar
+  , splits
+  , fillSig
+  , sig
+  ) where
+
+import Data.Char (isSymbol)
+import Data.List (find, intercalate)
+import Exception (ghandle, SomeException(..))
+import GHC (Ghc, LHsBind, LHsExpr, LPat, Id, ParsedModule(..), TypecheckedModule(..), DynFlags, SrcSpan, Type, GenLocated(L))
+import qualified GHC as G
+import Language.Haskell.GhcMod.Doc (showOneLine)
+import Language.Haskell.GhcMod.GHCApi
+import Language.Haskell.GhcMod.Gap (HasType(..))
+import qualified Language.Haskell.GhcMod.Gap as Gap
+import Language.Haskell.GhcMod.SrcUtils
+import Language.Haskell.GhcMod.Types
+import Language.Haskell.GhcMod.Convert
+import Outputable (PprStyle)
+import qualified Type as Ty
+import qualified TyCon as Ty
+import qualified DataCon as Ty
+import qualified HsBinds as Ty
+import qualified Class as Ty
+import OccName (OccName, occName)
+
+----------------------------------------------------------------
+
+data SplitInfo = SplitInfo G.Name (SrcSpan,Type) (SrcSpan, Type) [SrcSpan]
+
+-- | Splitting a variable in a equation.
+splitVar :: Options
+         -> Cradle
+         -> FilePath     -- ^ A target file.
+         -> Int          -- ^ Line number.
+         -> Int          -- ^ Column number.
+         -> IO String
+splitVar opt cradle file lineNo colNo = withGHC' $ do
+    initializeFlagsWithCradle opt cradle
+    splits opt file lineNo colNo
+
+-- | Splitting a variable in a equation.
+splits :: Options
+       -> FilePath     -- ^ A target file.
+       -> Int          -- ^ Line number.
+       -> Int          -- ^ Column number.
+       -> Ghc String
+splits opt file lineNo colNo = ghandle handler body
+  where
+    body = inModuleContext file $ \dflag style -> do
+        modSum <- Gap.fileModSummary file
+        splitInfo <- getSrcSpanTypeForSplit modSum lineNo colNo
+        case splitInfo of
+          Nothing -> return ""
+          Just (SplitInfo varName binding var@(_,varT) matches) -> do
+            return $ convert opt $ ( toTup dflag style binding
+                                   , toTup dflag style var
+                                   , (map fourInts matches)
+                                   , getTyCons dflag style varName varT)
+    handler (SomeException _) = return []
+
+getSrcSpanTypeForSplit :: G.ModSummary -> Int -> Int -> Ghc (Maybe SplitInfo)
+getSrcSpanTypeForSplit modSum lineNo colNo = do
+    p@ParsedModule{pm_parsed_source = pms} <- G.parseModule modSum
+    tcm@TypecheckedModule{tm_typechecked_source = tcs} <- G.typecheckModule p
+    let bs:_ = listifySpans tcs (lineNo, colNo) :: [LHsBind Id]
+        varPat  = find isPatternVar $ listifySpans tcs (lineNo, colNo) :: Maybe (LPat Id)
+        match:_ = listifyParsedSpans pms (lineNo, colNo) :: [G.LMatch G.RdrName (LHsExpr G.RdrName)]
+    case varPat of
+      Nothing  -> return Nothing
+      Just varPat' -> do
+        varT <- getType tcm varPat'  -- Finally we get the type of the var
+        bsT  <- getType tcm bs
+        case (varT, bsT) of
+          (Just varT', Just (_,bsT')) ->
+            let (L matchL (G.Match _ _ (G.GRHSs rhsLs _))) = match
+            in return $ Just (SplitInfo (getPatternVarName varPat') (matchL,bsT') varT' (map G.getLoc rhsLs) )
+          _ -> return Nothing
+
+isPatternVar :: LPat Id -> Bool
+isPatternVar (L _ (G.VarPat _)) = True
+isPatternVar _                  = False
+
+getPatternVarName :: LPat Id -> G.Name
+getPatternVarName (L _ (G.VarPat vName)) = G.getName vName
+getPatternVarName _                      = error "This should never happend"
+
+getTyCons :: DynFlags -> PprStyle -> G.Name -> G.Type ->  [String]
+getTyCons dflag style name ty | Just (tyCon, _) <- Ty.splitTyConApp_maybe ty =
+  let name' = showName dflag style name  -- Convert name to string
+  in getTyCon dflag style name' tyCon
+getTyCons dflag style name _ = [showName dflag style name]
+
+-- Write cases for one type
+getTyCon :: DynFlags -> PprStyle -> String -> Ty.TyCon -> [String]
+-- 1. Non-matcheable type constructors
+getTyCon _ _ name tyCon | isNotMatcheableTyCon tyCon = [name]
+-- 2. Special cases
+-- 2.1. Tuples
+getTyCon _ _ name tyCon | Ty.isTupleTyCon tyCon =
+  let [uniqueDataCon] = Ty.tyConDataCons tyCon
+      tupleArity = Ty.dataConSourceArity uniqueDataCon
+      -- Deal with both boxed and unboxed tuples
+      isUnboxed = Ty.isUnboxedTupleTyCon tyCon
+      startSign = if isUnboxed then "(#" else "("
+      endSign   = if isUnboxed then "#)" else ")"
+  in [ startSign ++ intercalate "," (map (\n -> name ++ show n) [1 .. tupleArity]) ++ endSign ]
+-- 3. General case
+getTyCon dflag style name tyCon = map (getDataCon dflag style name) (Ty.tyConDataCons tyCon)
+
+-- These type constructors should not be matched against
+isNotMatcheableTyCon :: Ty.TyCon -> Bool
+isNotMatcheableTyCon ty = Ty.isPrimTyCon ty  -- Primitive types, such as Int#
+                       || Ty.isFunTyCon ty   -- Function types
+
+-- Write case for one constructor
+getDataCon :: DynFlags -> PprStyle -> String -> Ty.DataCon -> String
+-- 1. Infix constructors
+getDataCon dflag style vName dcon | Ty.dataConIsInfix dcon =
+  let dName  = showName dflag style $ Ty.dataConName dcon
+  in case Ty.dataConSourceArity dcon of
+       0 -> dName
+       1 -> vName ++ dName
+       n -> if dName == ":" -- Special case for lists
+            then vName ++ ":" ++ vName ++ "s"
+            else newVar vName 1 ++ " " ++ dName ++ " " ++ newVars vName 2 (n-1)
+-- 2. Non-record, non-infix syntax
+getDataCon dflag style vName dcon | [] <- Ty.dataConFieldLabels dcon =
+  let dName  = showName dflag style $ Ty.dataConName dcon
+  in if last dName == '#'  -- Special case for I#, C# and so on
+     then vName
+     else dName ++ " " ++ newVarsSpecialSingleton vName 1 (Ty.dataConSourceArity dcon)
+-- 3. Records
+getDataCon dflag style vName dcon =
+  let dName = showName dflag style $ Ty.dataConName dcon
+      flds  = Ty.dataConFieldLabels dcon
+  in dName ++ " { " ++ showFieldNames dflag style vName flds ++ " }"
+
+-- Create a new variable by adjoining a number
+newVar :: String -> Int -> String
+newVar v n = v ++ show n
+
+-- Create a list of variables which start with the same prefix
+newVars :: String -> Int -> Int -> String
+newVars _ _ 0 = ""
+newVars v s 1 = newVar v s
+newVars v s m = newVar v s ++ " " ++ newVars v (s+1) (m-1)
+
+-- Create a list of variables which start with the same prefix
+-- Special case for a single variable, in which case no number is adjoint
+newVarsSpecialSingleton :: String -> Int -> Int -> String
+newVarsSpecialSingleton v _     1 = v
+newVarsSpecialSingleton v start n = newVars v start n
+
+showName :: DynFlags -> PprStyle -> G.Name -> String
+showName dflag style name = showOneLine dflag style $ Gap.nameForUser name
+
+showOccName :: DynFlags -> PprStyle -> OccName -> String
+showOccName dflag style name = showOneLine dflag style $ Gap.occNameForUser name
+
+showFieldNames :: DynFlags -> PprStyle -> String -> [G.Name] -> String
+showFieldNames _     _     _ []      = "" -- This should never happen
+showFieldNames dflag style v (x:xs) = let fName = showName dflag style x
+                                          fAcc  = fName ++ " = " ++ v ++ "_" ++ fName
+                                       in case xs of
+                                            [] -> fAcc
+                                            _  -> fAcc ++ ", " ++ showFieldNames dflag style v xs
+
+----------------------------------------------------------------
+
+data SigInfo = Signature SrcSpan [G.RdrName] (G.HsType G.RdrName)
+             | InstanceDecl SrcSpan G.Class
+
+-- | Create a initial body from a signature.
+fillSig :: Options
+        -> Cradle
+        -> FilePath     -- ^ A target file.
+        -> Int          -- ^ Line number.
+        -> Int          -- ^ Column number.
+        -> IO String
+fillSig opt cradle file lineNo colNo = withGHC' $ do
+    initializeFlagsWithCradle opt cradle
+    sig opt file lineNo colNo
+
+-- | Splitting a variable in a equation.
+sig :: Options
+       -> FilePath     -- ^ A target file.
+       -> Int          -- ^ Line number.
+       -> Int          -- ^ Column number.
+       -> Ghc String
+sig opt file lineNo colNo = ghandle handler body
+  where
+    body = inModuleContext file $ \dflag style -> do
+        modSum <- Gap.fileModSummary file
+        sigTy <- getSignature modSum lineNo colNo
+        case sigTy of
+          Nothing -> return ""
+          Just (Signature loc names ty) -> do
+            return $ convert opt $ ( fourInts loc
+                                   , map (initialFnBody dflag style ty) names
+                                   )
+          Just (InstanceDecl loc cls) -> do
+            return $ convert opt $ ( fourInts loc
+                                   , map (initialInstBody dflag style) (Ty.classMethods cls)
+                                   )
+            
+    handler (SomeException _) = return ""
+
+getSignature :: G.ModSummary -> Int -> Int -> Ghc (Maybe SigInfo)
+getSignature modSum lineNo colNo = do
+    p@ParsedModule{pm_parsed_source = ps} <- G.parseModule modSum
+    -- Look into the parse tree to find the signature
+    case listifyParsedSpans ps (lineNo, colNo) :: [G.LHsDecl G.RdrName] of
+      [L loc (G.SigD (Ty.TypeSig names (L _ ty)))] ->
+        -- We found a type signature
+        return $ Just $ Signature loc (map G.unLoc names) ty
+      [L _ (G.InstD _)] -> do
+        -- We found an instance declaration
+        TypecheckedModule{tm_renamed_source = Just tcs
+                         ,tm_checked_module_info = minfo} <- G.typecheckModule p
+        case listifyRenamedSpans tcs (lineNo, colNo) :: [G.LInstDecl G.Name] of
+          -- Instance declarations of sort 'instance F (G a)'
+          [L loc (G.ClsInstD (G.ClsInstDecl {G.cid_poly_ty =
+            (L _ (G.HsForAllTy _ _ _ (L _ (G.HsAppTy (L _ (G.HsTyVar clsName)) _))))}))] ->
+               obtainClassInfo minfo clsName loc
+          -- Instance declarations of sort 'instance F G' (no variables)
+          [L loc (G.ClsInstD (G.ClsInstDecl {G.cid_poly_ty =
+            (L _ (G.HsAppTy (L _ (G.HsTyVar clsName)) _))}))] ->
+               obtainClassInfo minfo clsName loc
+          _ -> return Nothing
+      _ -> return Nothing
+    where obtainClassInfo minfo clsName loc = do
+               tyThing <- G.modInfoLookupName minfo clsName
+               case tyThing of
+                 Just (Ty.ATyCon clsCon) -> 
+                   case G.tyConClass_maybe clsCon of
+                     Just cls -> return $ Just $ InstanceDecl loc cls
+                     Nothing  -> return Nothing
+                 _ -> return Nothing
+
+-- A list of function arguments, and whether they are functions or normal arguments
+-- is built from either a function signature or an instance signature
+data FnArg = FnArgFunction | FnArgNormal
+
+initialBody :: String -> [FnArg] -> String
+initialBody fname args =
+  case initialBodyArgs args infiniteVars infiniteFns of
+    []      -> fname
+    arglist -> if isSymbolName fname
+               then (head arglist) ++ " " ++ fname ++ " " ++ (intercalate " " (tail arglist))
+               else fname ++ " " ++ (intercalate " " arglist)
+  ++ " = _" ++ fname ++ "_body"
+
+initialBodyArgs :: [FnArg] -> [String] -> [String] -> [String]
+initialBodyArgs [] _ _ = []
+initialBodyArgs (FnArgFunction:xs) vs (f:fs) = f : initialBodyArgs xs vs fs
+initialBodyArgs (FnArgNormal:xs)   (v:vs) fs = v : initialBodyArgs xs vs fs
+initialBodyArgs _                  _      _  = error "This should never happen" -- Lists are infinite
+
+-- Getting the initial body of function and instances differ
+-- This is because for functions we only use the parsed file
+-- (so the full file doesn't have to be type correct)
+-- but for instances we need to get information about the class
+
+initialFnBody :: DynFlags -> PprStyle -> G.HsType G.RdrName -> G.RdrName -> String
+initialFnBody dflag style ty name = 
+  let fname = showOccName dflag style $ occName name  -- get function name
+      args  = \case (G.HsForAllTy _ _ _ (L _ iTy))  -> args iTy
+                    (G.HsParTy (L _ iTy))           -> args iTy
+                    (G.HsFunTy (L _ lTy) (L _ rTy)) -> (if fnarg lTy then FnArgFunction else FnArgNormal):args rTy
+                    _ -> []
+      fnarg = \case (G.HsForAllTy _ _ _ (L _ iTy)) -> fnarg iTy
+                    (G.HsParTy (L _ iTy))          -> fnarg iTy
+                    (G.HsFunTy _ _)                -> True
+                    _                              -> False
+   in initialBody fname (args ty)
+
+initialInstBody :: DynFlags -> PprStyle -> Id -> String
+initialInstBody dflag style method =
+  let fname = showOccName dflag style $ G.getOccName method  -- get function name
+      args  = \case ty | Just (lTy,rTy) <- Ty.splitFunTy_maybe ty ->
+                      case Ty.splitFunTy_maybe lTy of
+                        Just _  -> FnArgFunction:args rTy
+                        Nothing -> -- Drop the class predicates
+                                   if Ty.isPredTy lTy then args rTy else FnArgNormal:args rTy
+                    ty | Just (_,iTy) <- Ty.splitForAllTy_maybe ty -> args iTy
+                    _ -> []
+   in initialBody fname (args (Ty.dropForAlls $ G.idType method))
+
+infiniteVars, infiniteFns :: [String]
+infiniteVars = infiniteSupply ["x","y","z","t","u","v","w"]
+infiniteFns  = infiniteSupply ["f","g","h"]
+infiniteSupply :: [String] -> [String]
+infiniteSupply initialSupply = initialSupply ++ concatMap (\n -> map (\v -> v ++ show n) initialSupply) ([1 .. ] :: [Integer])
+
+isSymbolName :: String -> Bool
+isSymbolName (c:_) = c `elem` "!#$%&*+./<=>?@\\^|-~" || isSymbol c
+isSymbolName []    = error "This should never happen"
diff --git a/Language/Haskell/GhcMod/SrcUtils.hs b/Language/Haskell/GhcMod/SrcUtils.hs
new file mode 100644
index 0000000..c959500
--- /dev/null
+++ b/Language/Haskell/GhcMod/SrcUtils.hs
@@ -0,0 +1,77 @@
+{-# LANGUAGE TupleSections, FlexibleInstances, Rank2Types #-}
+{-# OPTIONS_GHC -fno-warn-orphans #-}
+
+module Language.Haskell.GhcMod.SrcUtils where
+
+import Control.Applicative ((<$>))
+import CoreMonad (liftIO)
+import CoreUtils (exprType)
+import Data.Generics
+import Data.Maybe (fromMaybe)
+import Data.Ord as O
+import GHC (Ghc, LHsExpr, LPat, Id, DynFlags, SrcSpan, Type, Located, ParsedSource, RenamedSource, TypecheckedSource, GenLocated(L))
+import qualified GHC as G
+import GHC.SYB.Utils (Stage(..), everythingStaged)
+import Language.Haskell.GhcMod.Doc (showOneLine, getStyle)
+import Language.Haskell.GhcMod.GHCApi
+import Language.Haskell.GhcMod.Gap (HasType(..), setWarnTypedHoles, setDeferTypeErrors)
+import qualified Language.Haskell.GhcMod.Gap as Gap
+import Outputable (PprStyle)
+import TcHsSyn (hsPatType)
+
+----------------------------------------------------------------
+
+instance HasType (LHsExpr Id) where
+    getType tcm e = do
+        hs_env <- G.getSession
+        mbe <- liftIO $ Gap.deSugar tcm e hs_env
+        return $ (G.getLoc e, ) <$> CoreUtils.exprType <$> mbe
+
+instance HasType (LPat Id) where
+    getType _ (G.L spn pat) = return $ Just (spn, hsPatType pat)
+
+----------------------------------------------------------------
+
+listifySpans :: Typeable a => TypecheckedSource -> (Int, Int) -> [Located a]
+listifySpans tcs lc = listifyStaged TypeChecker p tcs
+  where
+    p (L spn _) = G.isGoodSrcSpan spn && spn `G.spans` lc
+
+listifyParsedSpans :: Typeable a => ParsedSource -> (Int, Int) -> [Located a]
+listifyParsedSpans pcs lc = listifyStaged Parser p pcs
+  where
+    p (L spn _) = G.isGoodSrcSpan spn && spn `G.spans` lc
+
+listifyRenamedSpans :: Typeable a => RenamedSource -> (Int, Int) -> [Located a]
+listifyRenamedSpans pcs lc = listifyStaged Renamer p pcs
+  where
+    p (L spn _) = G.isGoodSrcSpan spn && spn `G.spans` lc
+
+listifyStaged :: Typeable r => Stage -> (r -> Bool) -> GenericQ [r]
+listifyStaged s p = everythingStaged s (++) [] ([] `mkQ` (\x -> [x | p x]))
+
+cmp :: SrcSpan -> SrcSpan -> Ordering
+cmp a b
+  | a `G.isSubspanOf` b = O.LT
+  | b `G.isSubspanOf` a = O.GT
+  | otherwise           = O.EQ
+
+toTup :: DynFlags -> PprStyle -> (SrcSpan, Type) -> ((Int,Int,Int,Int),String)
+toTup dflag style (spn, typ) = (fourInts spn, pretty dflag style typ)
+
+fourInts :: SrcSpan -> (Int,Int,Int,Int)
+fourInts = fromMaybe (0,0,0,0) . Gap.getSrcSpan
+
+pretty :: DynFlags -> PprStyle -> Type -> String
+pretty dflag style = showOneLine dflag style . Gap.typeForUser
+
+----------------------------------------------------------------
+
+inModuleContext :: FilePath -> (DynFlags -> PprStyle -> Ghc a) -> Ghc a
+inModuleContext file action =
+    withDynFlags (setWarnTypedHoles . setDeferTypeErrors . setNoWaringFlags) $ do
+    setTargetFiles [file]
+    Gap.withContext $ do
+        dflag <- G.getSessionDynFlags
+        style <- getStyle
+        action dflag style
diff --git a/ghc-mod.cabal b/ghc-mod.cabal
index 7699634..685f521 100644
--- a/ghc-mod.cabal
+++ b/ghc-mod.cabal
@@ -81,6 +81,8 @@ Library
                         Language.Haskell.GhcMod.Utils
                         Language.Haskell.GhcMod.Types
                         Language.Haskell.GhcMod.Read
+                        Language.Haskell.GhcMod.Rewrite
+                        Language.Haskell.GhcMod.SrcUtils
   Build-Depends:        base >= 4.0 && < 5
                       , containers
                       , deepseq