X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=Data%2FGenerics%2FSchemes.hs;h=4e75a823a020a01c338052ac03b94b00edf51579;hb=e0d697e559faf32d4b9f034c0968c1a299dd74c5;hp=c9aa40fac803cb08b89b90d1acb1cd32f9876715;hpb=83819904a18aa04e78ad1476a1640cce8388f470;p=ghc-base.git

diff --git a/Data/Generics/Schemes.hs b/Data/Generics/Schemes.hs
index c9aa40f..4e75a82 100644
--- a/Data/Generics/Schemes.hs
+++ b/Data/Generics/Schemes.hs
@@ -6,36 +6,45 @@
 -- 
 -- 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/>.
+-- See <http://www.cs.vu.nl/boilerplate/>. The present module provides
+-- frequently used generic traversal schemes.
 --
 -----------------------------------------------------------------------------
 
-module Data.Generics.Schemes ( 
+module Data.Generics.Schemes (
 
-	-- * Frequently used generic traversal schemes
         everywhere,
         everywhere',
         everywhereBut,
         everywhereM,
         somewhere,
-	everything,
-	listify,
+        everything,
+        listify,
         something,
-	synthesize,
+        synthesize,
+        gsize,
+        glength,
+        gdepth,
+        gcount,
+        gnodecount,
+        gtypecount,
+        gfindtype
 
  ) where
 
 ------------------------------------------------------------------------------
 
+#ifdef __HADDOCK__
+import Prelude
+#endif
 import Data.Generics.Basics
 import Data.Generics.Aliases
 import Control.Monad
 
 
-
 -- | Apply a transformation everywhere in bottom-up manner
 everywhere :: (forall a. Data a => a -> a)
            -> (forall a. Data a => a -> a)
@@ -89,7 +98,7 @@ everything :: (r -> r -> r) -> GenericQ r -> GenericQ r
 -- use gmapQ to recurse into immediate subterms;
 -- use ordinary foldl to reduce list of intermediate results
 -- 
-everything k f x 
+everything k f x
   = foldl k (f x) (gmapQ (everything k f) x)
 
 
@@ -111,7 +120,49 @@ something = everything orElse
 -- | Bottom-up synthesis of a data structure;
 --   1st argument z is the initial element for the synthesis;
 --   2nd argument o is for reduction of results from subterms;
---   3rd argument f updates the sythesised data according to the given term
+--   3rd argument f updates the synthesised data according to the given term
 --
-synthesize :: s  -> (s -> s -> s) -> GenericQ (s -> s) -> GenericQ s
+synthesize :: s  -> (t -> s -> s) -> GenericQ (s -> t) -> GenericQ t
 synthesize z o f x = f x (foldr o z (gmapQ (synthesize z o f) x))
+
+
+-- | Compute size of an arbitrary data structure
+gsize :: Data a => a -> Int
+gsize t = 1 + sum (gmapQ gsize t)
+
+
+-- | Count the number of immediate subterms of the given term
+glength :: GenericQ Int
+glength = length . gmapQ (const ())
+
+
+-- | Determine depth of the given term
+gdepth :: GenericQ Int
+gdepth = (+) 1 . foldr max 0 . gmapQ gdepth
+
+
+-- | Determine the number of all suitable nodes in a given term
+gcount :: GenericQ Bool -> GenericQ Int
+gcount p =  everything (+) (\x -> if p x then 1 else 0)
+
+
+-- | Determine the number of all nodes in a given term
+gnodecount :: GenericQ Int
+gnodecount = gcount (const True)
+
+
+-- | Determine the number of nodes of a given type in a given term
+gtypecount :: Typeable a => a -> GenericQ Int
+gtypecount (_::a) = gcount (False `mkQ` (\(_::a) -> True))
+
+
+-- | Find (unambiguously) an immediate subterm of a given type
+gfindtype :: (Data x, Typeable y) => x -> Maybe y
+gfindtype = singleton
+          . foldl unJust []
+          . gmapQ (Nothing `mkQ` Just)
+ where
+  unJust l (Just x) = x:l
+  unJust l Nothing  = l
+  singleton [s] = Just s
+  singleton _   = Nothing