-----------------------------------------------------------------------------
-- |
-- Module : Data.Generics.Aliases
--- Copyright : (c) The University of Glasgow, CWI 2001--2003
+-- Copyright : (c) The University of Glasgow, CWI 2001--2004
-- License : BSD-style (see the file libraries/base/LICENSE)
--
-- 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,
GenericR,
Generic,
Generic'(..),
+ GenericT'(..),
+ GenericQ'(..),
+ GenericM'(..),
-- * Inredients of generic functions
orElse,
choiceMp,
choiceQ,
- -- * Operators for (over-appreciated) unfolding
- gunfoldB,
- gunfoldR
+ -- * Type extension for unary type constructors
+ ext1T,
+ ext1M,
+ ext1Q,
+ ext1R
) where
-
+#ifdef __HADDOCK__
+import Prelude
+#endif
import Control.Monad
import Data.Generics.Basics
-
-
------------------------------------------------------------------------------
--
-- Combinators to "make" generic functions
=> (b -> b)
-> a
-> a
-mkT f = case cast f of
- Just g -> g
- Nothing -> id
+mkT = extT id
-- | Make a generic query;
=> (b -> m b)
-> a
-> m a
-mkM f = case castarr f of
- Just g -> g
- Nothing -> return
+mkM = extM return
{-
=> (b -> m b)
-> a
-> m a
-mkMp = maybe (const mzero) id . castarr
+mkMp = extM (const mzero)
-- | Make a generic builder;
, Typeable b
)
=> m b -> m a
-mkR = maybe mzero id . castss
+mkR f = mzero `extR` f
+
+
+-- | Flexible type extension
+ext0 :: (Typeable a, Typeable b) => c a -> c b -> c a
+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
, Typeable b
)
=> (a -> m a) -> (b -> m b) -> a -> m a
-extM f = maybe f id . castarr
+extM def ext = unM ((M def) `ext0` (M ext))
-- | Extend a generic MonadPlus transformation by a type-specific case
, Typeable b
)
=> m a -> m b -> m a
-extR f = maybe f id . castss
+extR def ext = unR ((R def) `ext0` (R ext))
+
------------------------------------------------------------------------------
-- | The general scheme underlying generic functions
-- assumed by gfoldl; there are isomorphisms such as
--- GenericT = Generic ID.
+-- GenericT = Generic T.
--
type Generic c = forall a. Data a => a -> c a
data Generic' c = Generic' { unGeneric' :: Generic c }
+-- | Other first-class polymorphic wrappers
+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
orElse :: Maybe a -> Maybe a -> Maybe a
------------------------------------------------------------------------------
--
--- Generic unfolding
+-- Type extension for unary type constructors
+--
+------------------------------------------------------------------------------
+
+
+
+-- | 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))
+
+
+
+------------------------------------------------------------------------------
+--
+-- Type constructors for type-level lambdas
--
------------------------------------------------------------------------------
--- | 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
+
+-- | The type constructor for transformations
+newtype T x = T { unT :: x -> x }
+
+-- | The type constructor for transformations
+newtype M m x = M { unM :: x -> m x }
+
+-- | The type constructor for queries
+newtype Q q x = Q { unQ :: x -> q }
+
+-- | The type constructor for readers
+newtype R m x = R { unR :: m x }
projects / haskell-directory.git / blobdiff