--
-- Maintainer : libraries@haskell.org
-- Stability : experimental
--- Portability : non-portable
+-- Portability : non-portable (local universal quantification)
--
-- \"Scrap your boilerplate\" --- Generic programming in Haskell
-- See <http://www.cs.vu.nl/boilerplate/>. The present module provides
-- * Combinators to \"make\" generic functions via cast
mkT, mkQ, mkM, mkMp, mkR,
- extT, extQ, extM, extMp, extB, extR,
+ ext0, extT, extQ, extM, extMp, extB, extR,
-- * Type synonyms for generic function types
GenericT,
choiceMp,
choiceQ,
- -- * Operators for (over-appreciated) unfolding
- gunfoldB,
- gunfoldR,
-
- -- * Type extension for lists
- extListT,
- extListM,
- extListQ,
- extListR
+ -- * Type extension for unary type constructors
+ ext1T,
+ ext1M,
+ ext1Q,
+ ext1R
) where
=> (b -> b)
-> a
-> a
-mkT f = case cast f of
- Just g -> g
- Nothing -> id
+mkT = extT id
-- | Make a generic query;
-- | Flexible type extension
ext0 :: (Typeable a, Typeable b) => c a -> c b -> c a
-ext0 def ext = maybe def id (cast0 ext)
+ext0 def ext = maybe def id (gcast ext)
-- | Extend a generic transformation by a type-specific case
extT :: ( Typeable a
- , Typeable b
+ , Typeable b
)
=> (a -> a)
-> (b -> b)
-> a
-> a
-extT f = maybe f id . cast
+extT def ext = unT ((T def) `ext0` (T ext))
-- | Extend a generic query by a type-specific case
-- | Other first-class polymorphic wrappers
-newtype GenericT' = GenericT' { unGenericT' :: Data a => a -> a }
-newtype GenericQ' r = GenericQ' { unGenericQ' :: GenericQ r }
-newtype GenericM' m = GenericM' { unGenericM' :: Data a => a -> m a }
+newtype GenericT' = GT { unGT :: Data a => a -> a }
+newtype GenericQ' r = GQ { unGQ :: GenericQ r }
+newtype GenericM' m = GM { unGM :: Data a => a -> m a }
-- | Left-biased choice on maybies
------------------------------------------------------------------------------
--
--- Generic unfolding
---
-------------------------------------------------------------------------------
-
--- | Construct an initial term with undefined immediate subterms
--- and then map over the skeleton to fill in proper terms.
-gunfoldB :: Data a
- => Constr
- -> (forall a. Data a => a)
- -> a
-gunfoldB c f = gmapT (const f) (fromConstr c)
-
-
--- | Monadic variation on \"gunfoldB\"
-gunfoldR :: (Monad m, Data a)
- => Constr
- -> (forall a. Data a => m a)
- -> m a
-gunfoldR c f = gmapM (const f) $ fromConstr c
-
-
-
-------------------------------------------------------------------------------
---
--- Type extension for lists
+-- Type extension for unary type constructors
--
------------------------------------------------------------------------------
--- | Type extension of transformations for lists
-extListT :: Data d
- => (forall d. Data d => d -> d)
- -> (forall d. Data d => [d] -> [d])
- -> d -> d
-extListT def ext = unT ((T def) `ext1` (T ext))
-
-
--- | Type extension of monadic transformations for lists
-extListM :: (Monad m, Data d)
- => (forall d. Data d => d -> m d)
- -> (forall d. Data d => [d] -> m [d])
- -> d -> m d
-extListM def ext = unM ((M def) `ext1` (M ext))
-
--- | Type extension of queries for lists
-extListQ :: Data d
- => (d -> q)
- -> (forall d. Data d => [d] -> q)
- -> d -> q
-extListQ def ext = unQ ((Q def) `ext1` (Q ext))
-
-
--- | Type extension of readers for lists
-extListR :: (Monad m, Data d)
- => m d
- -> (forall d. Data d => m [d])
- -> m d
-extListR def ext = unR ((R def) `ext1` (R ext))
+-- | Flexible type extension
+ext1 :: (Data a, Typeable1 t)
+ => c a
+ -> (forall a. Data a => c (t a))
+ -> c a
+ext1 def ext = maybe def id (dataCast1 ext)
+
+
+-- | Type extension of transformations for unary type constructors
+ext1T :: (Data d, Typeable1 t)
+ => (forall d. Data d => d -> d)
+ -> (forall d. Data d => t d -> t d)
+ -> d -> d
+ext1T def ext = unT ((T def) `ext1` (T ext))
+
+
+-- | Type extension of monadic transformations for type constructors
+ext1M :: (Monad m, Data d, Typeable1 t)
+ => (forall d. Data d => d -> m d)
+ -> (forall d. Data d => t d -> m (t d))
+ -> d -> m d
+ext1M def ext = unM ((M def) `ext1` (M ext))
+
+
+-- | Type extension of queries for type constructors
+ext1Q :: (Data d, Typeable1 t)
+ => (d -> q)
+ -> (forall d. Data d => t d -> q)
+ -> d -> q
+ext1Q def ext = unQ ((Q def) `ext1` (Q ext))
+
+
+-- | Type extension of readers for type constructors
+ext1R :: (Monad m, Data d, Typeable1 t)
+ => m d
+ -> (forall d. Data d => m (t d))
+ -> m d
+ext1R def ext = unR ((R def) `ext1` (R ext))