[project @ 2003-06-05 13:42:51 by ralf]

Add listify; other minor revisions.

diff --git a/Data/Generics.hs b/Data/Generics.hs
index 0f79a34..4132aa2 100644 (file)
--- a/Data/Generics.hs
+++ b/Data/Generics.hs
@@ -51,6 +51,7 @@ module Data.Generics (
         everywhereM,
         somewhere,
        everything,
+       listify,
         something,
        synthesize,
 
@@ -509,7 +510,13 @@ everything :: (r -> r -> r) -> GenericQ r -> GenericQ r
 -- use ordinary foldl to reduce list of intermediate results
 -- 
 everything k f x 
-     = foldl k (f x) (gmapQ (everything k f) x)
+  = foldl k (f x) (gmapQ (everything k f) x)
+
+
+-- | Get a list of all entities that meet a predicate
+listify :: Typeable r => (r -> Bool) -> GenericQ [r]
+listify p
+  = everything (++) ([] `mkQ` (\x -> if p x then [x] else []))
 
 
 -- | Look up a subterm by means of a maybe-typed filter