Add StackSet.filter

darcs-hash:20070611165154-a5988-8c46751ffd4bd03249656e3b467b8e7569c48b09

2 files changed, 16 insertions, 3 deletions

diff --git a/StackSet.hs b/StackSet.hs
index 619d536..1b258fc 100644
--- a/StackSet.hs
+++ b/StackSet.hs
@@ -76,12 +76,13 @@
 module StackSet (
         StackSet(..), Workspace(..), Screen(..), Stack(..), RationalRect(..),
         new, view, lookupWorkspace, peek, index, integrate, focusUp, focusDown,
-        focusWindow, member, findIndex, insertUp, delete, shift,
+        focusWindow, member, findIndex, insertUp, delete, shift, filter,
         swapMaster, swapUp, swapDown, modify, float, sink -- needed by users
     ) where
 
+import Prelude hiding (filter)
 import Data.Maybe   (listToMaybe)
-import qualified Data.List as L (delete,find,genericSplitAt)
+import qualified Data.List as L (delete,find,genericSplitAt,filter)
 import qualified Data.Map  as M (Map,insert,delete,empty)
 
 -- | 
@@ -262,6 +263,18 @@ integrate Empty        = []
 integrate (Node x l r) = reverse l ++ x : r
 
 -- |
+-- /O(n)/. 'filter p s' returns the elements of 's' such that 'p' evaluates to
+-- True.  Order is preserved, and focus moves to the next node to the right (if
+-- necessary).
+filter :: (a -> Bool) -> Stack a -> Stack a
+filter p Empty          = Empty
+filter p (Node f ls rs) = case L.filter p (f:rs) of
+                            (f':rs') -> Node f' (L.filter p ls) rs'
+                            []       -> case reverse $ L.filter p ls of
+                                            []       -> Empty
+                                            (f':rs') -> Node f' [] rs'
+
+-- |
 -- /O(s)/. Extract the stack on the current workspace, as a list.
 -- The order of the stack is determined by the master window -- it will be
 -- the head of the list. The implementation is given by the natural
diff --git a/tests/Properties.hs b/tests/Properties.hs
index 8a2d712..06e32a5 100644
--- a/tests/Properties.hs
+++ b/tests/Properties.hs
@@ -1,6 +1,6 @@
 {-# OPTIONS -fglasgow-exts #-}
 
-import StackSet
+import StackSet hiding (filter)
 import Operations (tile)
 
 import Debug.Trace