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185 lines
7.1 KiB
Haskell
185 lines
7.1 KiB
Haskell
-----------------------------------------------------------------------------
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-- |
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-- Module : StackSet
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-- Copyright : (c) Don Stewart 2007
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-- License : BSD3-style (see LICENSE)
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--
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-- Maintainer : dons@cse.unsw.edu.au
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-- Stability : stable
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-- Portability : portable, needs GHC 6.6
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--
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-----------------------------------------------------------------------------
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--
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-- The 'StackSet' data type encodes a set of stacks. A given stack in the
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-- set is always current. Elements may appear only once in the entire
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-- stack set.
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--
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-- A StackSet provides a nice data structure for multiscreen
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-- window managers, where each screen has a stack of windows, and a window
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-- may be on only 1 screen at any given time.
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--
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module StackSet where
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import Data.Maybe
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import qualified Data.List as L (delete)
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import qualified Data.Map as M
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------------------------------------------------------------------------
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--
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-- N.B we probably want to think about strict 'adjust' and inserts on
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-- these data structures in the long run.
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--
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-- | The StackSet data structure. A table of stacks, with a current pointer
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data StackSet a =
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StackSet
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{ current:: {-# UNPACK #-} !Int -- ^ the currently visible stack
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, stacks :: {-# UNPACK #-} !(M.Map Int [a]) -- ^ the separate stacks
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, focus :: {-# UNPACK #-} !(M.Map Int a) -- ^ the window focused in each stack
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, cache :: {-# UNPACK #-} !(M.Map a Int) -- ^ a cache of windows back to their stacks
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} deriving Eq
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instance Show a => Show (StackSet a) where
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showsPrec p s r = showsPrec p (show . toList $ s) r
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-- Ord a constraint on 'a' as we use it as a key.
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--
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-- The cache is used to check on insertion that we don't already have
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-- this window managed on another stack
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------------------------------------------------------------------------
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-- | /O(n)/. Create a new empty stacks of size 'n', indexed from 0. The
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-- 0-indexed stack will be current.
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empty :: Int -> StackSet a
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empty n = StackSet { current = 0
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, stacks = M.fromList (zip [0..n-1] (repeat []))
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, focus = M.empty
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, cache = M.empty }
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-- | /O(log w)/. True if x is somewhere in the StackSet
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member :: Ord a => a -> StackSet a -> Bool
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member a w = M.member a (cache w)
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-- | /O(log n)/. Looks up the stack that x is in, if it is in the StackSet
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lookup :: (Monad m, Ord a) => a -> StackSet a -> m Int
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lookup x w = M.lookup x (cache w)
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-- | /O(n)/. Number of stacks
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size :: StackSet a -> Int
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size = M.size . stacks
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------------------------------------------------------------------------
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-- | fromList. Build a new StackSet from a list of list of elements
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-- If there are duplicates in the list, the last occurence wins.
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fromList :: Ord a => (Int,[[a]]) -> StackSet a
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fromList (_,[]) = error "Cannot build a StackSet from an empty list"
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fromList (n,xs) | n < 0 || n >= length xs
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= error $ "Cursor index is out of range: " ++ show (n, length xs)
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fromList (o,xs) = view o $ foldr (\(i,ys) s ->
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foldr (\a t -> insert a i t) s ys)
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(empty (length xs)) (zip [0..] xs)
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-- | toList. Flatten a stackset to a list of lists
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toList :: StackSet a -> (Int,[[a]])
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toList x = (current x, map snd $ M.toList (stacks x))
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-- | Push. Insert an element onto the top of the current stack.
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-- If the element is already in the current stack, it is moved to the top.
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-- If the element is managed on another stack, it is removed from that
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-- stack first.
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push :: Ord a => a -> StackSet a -> StackSet a
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push k w = insert k (current w) w
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-- | /O(log s)/. Extract the element on the top of the current stack. If no such
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-- element exists, Nothing is returned.
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peek :: StackSet a -> Maybe a
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peek w = peekStack (current w) w
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-- | /O(log s)/. Extract the element on the top of the given stack. If no such
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-- element exists, Nothing is returned.
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peekStack :: Int -> StackSet a -> Maybe a
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peekStack n w = M.lookup n (focus w)
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-- | /O(log s)/. Index. Extract the stack at index 'n'.
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-- If the index is invalid, an exception is thrown.
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index :: Int -> StackSet a -> [a]
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index k w = fromJust (M.lookup k (stacks w))
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-- | /O(1)/. view. Set the stack specified by the Int argument as being the
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-- current StackSet. If the index is out of range an exception is thrown.
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view :: Int -> StackSet a -> StackSet a
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view n w | n >= 0 && n < M.size (stacks w) = w { current = n }
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| otherwise = error $ "view: index out of bounds: " ++ show n
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-- | /O(log n)/. rotate. cycle the current window list up or down.
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--
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-- rotate EQ --> [5,6,7,8,1,2,3,4]
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-- rotate GT --> [6,7,8,1,2,3,4,5]
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-- rotate LT --> [4,5,6,7,8,1,2,3]
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--
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-- where xs = [5..8] ++ [1..4]
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--
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rotate :: Eq a => Ordering -> StackSet a -> StackSet a
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rotate o w = maybe w id $ do
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f <- M.lookup (current w) (focus w)
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s <- M.lookup (current w) (stacks w)
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ea <- case o of
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EQ -> Nothing
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GT -> elemAfter f s
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LT -> elemAfter f (reverse s)
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return (w { focus = M.insert (current w) ea (focus w) })
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-- | /O(log n)/. shift. move the client on top of the current stack to
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-- the top of stack 'n'. If the stack to move to is not valid, and
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-- exception is thrown.
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--
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shift :: Ord a => Int -> StackSet a -> StackSet a
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shift n w = maybe w (\k -> insert k n (delete k w)) (peek w)
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-- | /O(log n)/. Insert an element onto the top of stack 'n'.
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-- If the element is already in the stack 'n', it is moved to the top.
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-- If the element exists on another stack, it is removed from that stack.
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-- If the index is wrong an exception is thrown.
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--
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insert :: Ord a => a -> Int -> StackSet a -> StackSet a
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insert k n old = new { cache = M.insert k n (cache new)
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, stacks = M.adjust (k:) n (stacks new)
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, focus = M.insert n k (focus new) }
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where new = delete k old
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-- | /O(log n)/. Delete an element entirely from from the StackSet.
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-- This can be used to ensure that a given element is not managed elsewhere.
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-- If the element doesn't exist, the original StackSet is returned unmodified.
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delete :: Ord a => a -> StackSet a -> StackSet a
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delete k w = maybe w tweak (M.lookup k (cache w))
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where
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tweak i = w { cache = M.delete k (cache w)
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, stacks = M.adjust (L.delete k) i (stacks w)
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, focus = M.update (\k' -> if k == k' then elemAfter k (stacks w M.! i)
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else Just k') i
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(focus w)
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}
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-- | /O(log n)/. If the given window is contained in a workspace, make it the
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-- focused window of that workspace, and make that workspace the current one.
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raiseFocus :: Ord a => a -> StackSet a -> StackSet a
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raiseFocus k w = case M.lookup k (cache w) of
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Nothing -> w
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Just i -> w { focus = M.insert i k (focus w), current = i }
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-- | Move a window to the top of its workspace.
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promote :: Ord a => a -> StackSet a -> StackSet a
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promote k w = case M.lookup k (cache w) of
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Nothing -> w
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Just i -> w { stacks = M.adjust (\ks -> k : filter (/= k) ks) i (stacks w) }
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-- |
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elemAfter :: Eq a => a -> [a] -> Maybe a
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elemAfter w ws = listToMaybe . filter (/= w) . dropWhile (/= w) $ ws ++ ws
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