-------------------------------------------------------------------------------- -- | -- Module : Data.Comp.Derive.Utils -- Copyright : (c) 2010-2011 Patrick Bahr -- License : BSD3 -- Maintainer : Patrick Bahr -- Stability : experimental -- Portability : non-portable (GHC Extensions) -- -- This module defines some utility functions for deriving instances -- for functor based type classes. -- -------------------------------------------------------------------------------- module Data.Comp.Derive.Utils where import Language.Haskell.TH import Language.Haskell.TH.Syntax import Control.Monad import Language.Haskell.TH.ExpandSyns {-| This is the @Q@-lifted version of 'abstractNewtypeQ. -} abstractNewtypeQ :: Q Info -> Q Info abstractNewtypeQ = liftM abstractNewtype {-| This function abstracts away @newtype@ declaration, it turns them into @data@ declarations. -} abstractNewtype :: Info -> Info abstractNewtype (TyConI (NewtypeD cxt name args constr derive)) = TyConI (DataD cxt name args [constr] derive) abstractNewtype owise = owise {-| This function provides the name and the arity of the given data constructor. -} normalCon :: Con -> (Name,[StrictType]) normalCon (NormalC constr args) = (constr, args) normalCon (RecC constr args) = (constr, map (\(_,s,t) -> (s,t)) args) normalCon (InfixC a constr b) = (constr, [a,b]) normalCon (ForallC _ _ constr) = normalCon constr normalCon' :: Con -> (Name,[Type]) normalCon' = fmap (map snd) . normalCon -- | Same as normalCon' but expands type synonyms. normalConExp :: Con -> Q (Name,[Type]) normalConExp c = do let (n,ts) = normalCon' c ts' <- mapM expandSyns ts return (n, ts') -- | Same as normalConExp' but retains strictness annotations. normalConStrExp :: Con -> Q (Name,[StrictType]) normalConStrExp c = do let (n,ts) = normalCon c ts' <- mapM (\ (st,ty) -> do ty' <- expandSyns ty; return (st,ty')) ts return (n, ts') {-| This function provides the name and the arity of the given data constructor. -} abstractConType :: Con -> (Name,Int) abstractConType (NormalC constr args) = (constr, length args) abstractConType (RecC constr args) = (constr, length args) abstractConType (InfixC _ constr _) = (constr, 2) abstractConType (ForallC _ _ constr) = abstractConType constr {-| This function returns the name of a bound type variable -} tyVarBndrName (PlainTV n) = n tyVarBndrName (KindedTV n _) = n containsType :: Type -> Type -> Bool containsType s t | s == t = True | otherwise = case s of ForallT _ _ s' -> containsType s' t AppT s1 s2 -> containsType s1 t || containsType s2 t SigT s' _ -> containsType s' t _ -> False containsType' :: Type -> Type -> [Int] containsType' = run 0 where run n s t | s == t = [n] | otherwise = case s of ForallT _ _ s' -> run n s' t -- only going through the right-hand side counts! AppT s1 s2 -> run n s1 t ++ run (n+1) s2 t SigT s' _ -> run n s' t _ -> [] {-| This function provides a list (of the given length) of new names based on the given string. -} newNames :: Int -> String -> Q [Name] newNames n name = replicateM n (newName name) tupleTypes n m = map tupleTypeName [n..m] {-| Helper function for generating a list of instances for a list of named signatures. For example, in order to derive instances 'Functor' and 'ShowF' for a signature @Exp@, use derive as follows (requires Template Haskell): > $(derive [makeFunctor, makeShowF] [''Exp]) -} derive :: [Name -> Q [Dec]] -> [Name] -> Q [Dec] derive ders names = liftM concat $ sequence [der name | der <- ders, name <- names] -- | This function lifts type class instances over sums -- ofsignatures. To this end it assumes that it contains only methods -- with types of the form @f t1 .. tn -> t@ where @f@ is the signature -- that is used to construct sums. Since this function is generic it -- assumes as its first argument the name of the function that is -- used to lift methods over sums i.e. a function of type -- -- @ -- (f t1 .. tn -> t) -> (g t1 .. tn -> t) -> ((f :+: g) t1 .. tn -> t) -- @ -- -- where @:+:@ is the sum type constructor. The second argument to -- this function is expected to be the name of that constructor. The -- last argument is the name of the class whose instances should be -- lifted over sums. liftSumGen :: Name -> Name -> Name -> Q [Dec] liftSumGen caseName sumName fname = do ClassI (ClassD _ name targs_ _ decs) _ <- reify fname let targs = map tyVarBndrName targs_ splitM <- findSig targs decs case splitM of Nothing -> do report True $ "Class " ++ show name ++ " cannot be lifted to sums!" return [] Just (ts1_, ts2_) -> do let f = VarT $ mkName "f" let g = VarT $ mkName "g" let ts1 = map VarT ts1_ let ts2 = map VarT ts2_ let cxt = [ClassP name (ts1 ++ f : ts2), ClassP name (ts1 ++ g : ts2)] let tp = ((ConT sumName `AppT` f) `AppT` g) let complType = foldl AppT (foldl AppT (ConT name) ts1 `AppT` tp) ts2 decs' <- sequence $ concatMap decl decs return [InstanceD cxt complType decs'] where decl :: Dec -> [DecQ] decl (SigD f _) = [funD f [clause f]] decl _ = [] clause :: Name -> ClauseQ clause f = do x <- newName "x" let b = NormalB (VarE caseName `AppE` VarE f `AppE` VarE f `AppE` VarE x) return $ Clause [VarP x] b [] findSig :: [Name] -> [Dec] -> Q (Maybe ([Name],[Name])) findSig targs decs = case map run decs of [] -> return Nothing mx:_ -> do x <- mx case x of Nothing -> return Nothing Just n -> return $ splitNames n targs where run :: Dec -> Q (Maybe Name) run (SigD _ ty) = do ty' <- expandSyns ty return $ getSig False ty' run _ = return Nothing getSig t (ForallT _ _ ty) = getSig t ty getSig False (AppT (AppT ArrowT ty) _) = getSig True ty getSig True (AppT ty _) = getSig True ty getSig True (VarT n) = Just n getSig _ _ = Nothing splitNames y (x:xs) | y == x = Just ([],xs) | otherwise = do (xs1,xs2) <- splitNames y xs return (x:xs1,xs2) splitNames _ [] = Nothing