X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;ds=sidebyside;f=Data%2FGenerics%2FAliases.hs;fp=Data%2FGenerics%2FAliases.hs;h=3c662988e3f20341d0d46be1a01fba6b53bf31bf;hb=fbc83401e9196b75601ab3f6c13e6c83e0b39f31;hp=3c03f56bc5976d3bf2a618aee1eadb3c13c3161c;hpb=c965627e2ab998114be853ce9c1a7c006aca8e12;p=haskell-directory.git

diff --git a/Data/Generics/Aliases.hs b/Data/Generics/Aliases.hs
index 3c03f56..3c66298 100644
--- a/Data/Generics/Aliases.hs
+++ b/Data/Generics/Aliases.hs
@@ -336,6 +336,15 @@ gunfoldR c f = gmapM (const f) $ fromConstr c
 ------------------------------------------------------------------------------
 
 
+
+-- | 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 (cast0to1 ext)
+
+
 -- | Type extension of transformations for unary type constructors
 ext1T :: (Data d, Typeable1 t)
       => (forall d. Data d => d -> d)