{-# LANGUAGE FlexibleInstances, MultiParamTypeClasses, PatternGuards #-}

-----------------------------------------------------------------------------
-- |
-- Module      :  XMonad.Layout.Gaps
-- Description :  Create manually-sized gaps along edges of the screen.
-- Copyright   :  (c) 2008 Brent Yorgey
-- License     :  BSD3
--
-- Maintainer  :  <byorgey@gmail.com>
-- Stability   :  unstable
-- Portability :  unportable
--
-- Create manually-sized gaps along edges of the screen which will not
-- be used for tiling, along with support for toggling gaps on and
-- off.
--
-- Note 1: For gaps\/space around /windows/ see "XMonad.Layout.Spacing".
--
-- Note 2: "XMonad.Hooks.ManageDocks" is the preferred solution for
-- leaving space for your dock-type applications (status bars,
-- toolbars, docks, etc.), since it automatically sets up appropriate
-- gaps, allows them to be toggled, etc.  However, this module may
-- still be useful in some situations where the automated approach of
-- ManageDocks does not work; for example, to work with a dock-type
-- application that does not properly set the STRUTS property, or to
-- leave part of the screen blank which is truncated by a projector,
-- and so on.
-----------------------------------------------------------------------------

module XMonad.Layout.Gaps (
                               -- * Usage
                               -- $usage
                          Direction2D(..), Gaps,
                          GapSpec, gaps, gaps', GapMessage(..),
                          weakModifyGaps, modifyGap, setGaps, setGap
                          ) where

import XMonad.Prelude (delete, fi)
import XMonad.Core
import Graphics.X11 (Rectangle(..))

import XMonad.Layout.LayoutModifier
import XMonad.Util.Types (Direction2D(..))

-- $usage
-- You can use this module by importing it into your @~\/.xmonad\/xmonad.hs@ file:
--
-- > import XMonad.Layout.Gaps
--
-- and applying the 'gaps' modifier to your layouts as follows (for
-- example):
--
-- > layoutHook = gaps [(U,18), (R,23)] $ Tall 1 (3/100) (1/2) ||| Full  -- leave gaps at the top and right
--
-- You can additionally add some keybindings to toggle or modify the gaps,
-- for example:
--
-- > , ((modm .|. controlMask, xK_g), sendMessage $ ToggleGaps)               -- toggle all gaps
-- > , ((modm .|. controlMask, xK_t), sendMessage $ ToggleGap U)              -- toggle the top gap
-- > , ((modm .|. controlMask, xK_w), sendMessage $ IncGap 5 R)               -- increment the right-hand gap
-- > , ((modm .|. controlMask, xK_q), sendMessage $ DecGap 5 R)               -- decrement the right-hand gap
-- > , ((modm .|. controlMask, xK_r), sendMessage $ ModifyGaps rotateGaps)    -- rotate gaps 90 degrees clockwise
-- > , ((modm .|. controlMask, xK_h), sendMessage $ weakModifyGaps halveHor)  -- halve the left and right-hand gaps
-- > , ((modm .|. controlMask, xK_d), sendMessage $ modifyGap (*2) L)         -- double the left-hand gap
-- > , ((modm .|. controlMask, xK_s), sendMessage $ setGaps [(U,18), (R,23)]) -- reset the GapSpec
-- > , ((modm .|. controlMask, xK_b), sendMessage $ setGap 30 D)              -- set the bottom gap to 30
-- > ]
-- >   where rotateGaps gs = zip (map (rotate . fst) gs) (map snd gs)
-- >         rotate U = R
-- >         rotate R = D
-- >         rotate D = L
-- >         rotate L = U
-- >         halveHor d i | d `elem` [L, R] = i `div` 2
-- >                      | otherwise       = i
--
-- If you want complete control over all gaps, you could include
-- something like this in your keybindings, assuming in this case you
-- are using 'XMonad.Util.EZConfig.mkKeymap' or
-- 'XMonad.Util.EZConfig.additionalKeysP' from "XMonad.Util.EZConfig"
-- for string keybinding specifications:
--
-- > ++
-- > [ ("M-g " ++ f ++ " " ++ k, sendMessage $ m d)
-- >     | (k, d) <- [("a",L), ("s",D), ("w",U), ("d",R)]
-- >     , (f, m) <- [("v", ToggleGap), ("h", IncGap 10), ("f", DecGap 10)]
-- > ]
--
-- Given the above keybinding definition, for example, you could type
-- @M-g, v, a@ to toggle the top gap.
--
-- To configure gaps differently per-screen, use
-- "XMonad.Layout.PerScreen" (coming soon).
--
-- __Warning__: If you also use the 'avoidStruts' layout modifier, it
-- must come /before/ any of these modifiers. See the documentation of
-- 'avoidStruts' for details.

-- | A manual gap configuration.  Each side of the screen on which a
--   gap is enabled is paired with a size in pixels.
type GapSpec = [(Direction2D,Int)]

-- | The gap state.  The first component is the configuration (which
--   gaps are allowed, and their current size), the second is the gaps
--   which are currently active.
data Gaps a = Gaps GapSpec [Direction2D]
  deriving (Int -> Gaps a -> ShowS
[Gaps a] -> ShowS
Gaps a -> String
(Int -> Gaps a -> ShowS)
-> (Gaps a -> String) -> ([Gaps a] -> ShowS) -> Show (Gaps a)
forall a. Int -> Gaps a -> ShowS
forall a. [Gaps a] -> ShowS
forall a. Gaps a -> String
forall a.
(Int -> a -> ShowS) -> (a -> String) -> ([a] -> ShowS) -> Show a
showList :: [Gaps a] -> ShowS
$cshowList :: forall a. [Gaps a] -> ShowS
show :: Gaps a -> String
$cshow :: forall a. Gaps a -> String
showsPrec :: Int -> Gaps a -> ShowS
$cshowsPrec :: forall a. Int -> Gaps a -> ShowS
Show, ReadPrec [Gaps a]
ReadPrec (Gaps a)
Int -> ReadS (Gaps a)
ReadS [Gaps a]
(Int -> ReadS (Gaps a))
-> ReadS [Gaps a]
-> ReadPrec (Gaps a)
-> ReadPrec [Gaps a]
-> Read (Gaps a)
forall a. ReadPrec [Gaps a]
forall a. ReadPrec (Gaps a)
forall a. Int -> ReadS (Gaps a)
forall a. ReadS [Gaps a]
forall a.
(Int -> ReadS a)
-> ReadS [a] -> ReadPrec a -> ReadPrec [a] -> Read a
readListPrec :: ReadPrec [Gaps a]
$creadListPrec :: forall a. ReadPrec [Gaps a]
readPrec :: ReadPrec (Gaps a)
$creadPrec :: forall a. ReadPrec (Gaps a)
readList :: ReadS [Gaps a]
$creadList :: forall a. ReadS [Gaps a]
readsPrec :: Int -> ReadS (Gaps a)
$creadsPrec :: forall a. Int -> ReadS (Gaps a)
Read)

-- | Messages which can be sent to a gap modifier.
data GapMessage = ToggleGaps              -- ^ Toggle all gaps.
                | ToggleGap  !Direction2D    -- ^ Toggle a single gap.
                | IncGap !Int !Direction2D    -- ^ Increase a gap by a certain number of pixels.
                | DecGap !Int !Direction2D    -- ^ Decrease a gap.
                | ModifyGaps (GapSpec -> GapSpec) -- ^ Modify arbitrarily.

instance Message GapMessage

instance LayoutModifier Gaps a where
    modifyLayout :: forall (l :: * -> *).
LayoutClass l a =>
Gaps a
-> Workspace String (l a) a
-> Rectangle
-> X ([(a, Rectangle)], Maybe (l a))
modifyLayout Gaps a
g Workspace String (l a) a
w Rectangle
r = Workspace String (l a) a
-> Rectangle -> X ([(a, Rectangle)], Maybe (l a))
forall (layout :: * -> *) a.
LayoutClass layout a =>
Workspace String (layout a) a
-> Rectangle -> X ([(a, Rectangle)], Maybe (layout a))
runLayout Workspace String (l a) a
w (Gaps a -> Rectangle -> Rectangle
forall a. Gaps a -> Rectangle -> Rectangle
applyGaps Gaps a
g Rectangle
r)

    pureMess :: Gaps a -> SomeMessage -> Maybe (Gaps a)
pureMess (Gaps GapSpec
conf [Direction2D]
cur) SomeMessage
m
      | Just GapMessage
ToggleGaps    <- SomeMessage -> Maybe GapMessage
forall m. Message m => SomeMessage -> Maybe m
fromMessage SomeMessage
m
        = Gaps a -> Maybe (Gaps a)
forall a. a -> Maybe a
Just (Gaps a -> Maybe (Gaps a)) -> Gaps a -> Maybe (Gaps a)
forall a b. (a -> b) -> a -> b
$ GapSpec -> [Direction2D] -> Gaps a
forall a. GapSpec -> [Direction2D] -> Gaps a
Gaps GapSpec
conf (GapSpec -> [Direction2D] -> [Direction2D]
toggleGaps GapSpec
conf [Direction2D]
cur)
      | Just (ToggleGap Direction2D
d) <- SomeMessage -> Maybe GapMessage
forall m. Message m => SomeMessage -> Maybe m
fromMessage SomeMessage
m
        = Gaps a -> Maybe (Gaps a)
forall a. a -> Maybe a
Just (Gaps a -> Maybe (Gaps a)) -> Gaps a -> Maybe (Gaps a)
forall a b. (a -> b) -> a -> b
$ GapSpec -> [Direction2D] -> Gaps a
forall a. GapSpec -> [Direction2D] -> Gaps a
Gaps GapSpec
conf (GapSpec -> [Direction2D] -> Direction2D -> [Direction2D]
toggleGap GapSpec
conf [Direction2D]
cur Direction2D
d)
      | Just (IncGap Int
i Direction2D
d)  <- SomeMessage -> Maybe GapMessage
forall m. Message m => SomeMessage -> Maybe m
fromMessage SomeMessage
m
        = Gaps a -> Maybe (Gaps a)
forall a. a -> Maybe a
Just (Gaps a -> Maybe (Gaps a)) -> Gaps a -> Maybe (Gaps a)
forall a b. (a -> b) -> a -> b
$ GapSpec -> [Direction2D] -> Gaps a
forall a. GapSpec -> [Direction2D] -> Gaps a
Gaps (GapSpec -> GapSpec
limit (GapSpec -> GapSpec) -> (GapSpec -> GapSpec) -> GapSpec -> GapSpec
forall b c a. (b -> c) -> (a -> b) -> a -> c
. (Int -> Int) -> Direction2D -> GapSpec -> GapSpec
continuation (Int -> Int -> Int
forall a. Num a => a -> a -> a
+  Int
i ) Direction2D
d (GapSpec -> GapSpec) -> GapSpec -> GapSpec
forall a b. (a -> b) -> a -> b
$ GapSpec
conf) [Direction2D]
cur
      | Just (DecGap Int
i Direction2D
d)  <- SomeMessage -> Maybe GapMessage
forall m. Message m => SomeMessage -> Maybe m
fromMessage SomeMessage
m
        = Gaps a -> Maybe (Gaps a)
forall a. a -> Maybe a
Just (Gaps a -> Maybe (Gaps a)) -> Gaps a -> Maybe (Gaps a)
forall a b. (a -> b) -> a -> b
$ GapSpec -> [Direction2D] -> Gaps a
forall a. GapSpec -> [Direction2D] -> Gaps a
Gaps (GapSpec -> GapSpec
limit (GapSpec -> GapSpec) -> (GapSpec -> GapSpec) -> GapSpec -> GapSpec
forall b c a. (b -> c) -> (a -> b) -> a -> c
. (Int -> Int) -> Direction2D -> GapSpec -> GapSpec
continuation (Int -> Int -> Int
forall a. Num a => a -> a -> a
+(-Int
i)) Direction2D
d (GapSpec -> GapSpec) -> GapSpec -> GapSpec
forall a b. (a -> b) -> a -> b
$ GapSpec
conf) [Direction2D]
cur
      | Just (ModifyGaps GapSpec -> GapSpec
f) <- SomeMessage -> Maybe GapMessage
forall m. Message m => SomeMessage -> Maybe m
fromMessage SomeMessage
m
        = Gaps a -> Maybe (Gaps a)
forall a. a -> Maybe a
Just (Gaps a -> Maybe (Gaps a)) -> Gaps a -> Maybe (Gaps a)
forall a b. (a -> b) -> a -> b
$ GapSpec -> [Direction2D] -> Gaps a
forall a. GapSpec -> [Direction2D] -> Gaps a
Gaps (GapSpec -> GapSpec
limit (GapSpec -> GapSpec) -> (GapSpec -> GapSpec) -> GapSpec -> GapSpec
forall b c a. (b -> c) -> (a -> b) -> a -> c
. GapSpec -> GapSpec
f (GapSpec -> GapSpec) -> GapSpec -> GapSpec
forall a b. (a -> b) -> a -> b
$ GapSpec
conf) [Direction2D]
cur
      | Bool
otherwise = Maybe (Gaps a)
forall a. Maybe a
Nothing

-- | Modifies gaps weakly, for convenience.
weakModifyGaps :: (Direction2D -> Int -> Int) -> GapMessage
weakModifyGaps :: (Direction2D -> Int -> Int) -> GapMessage
weakModifyGaps = (GapSpec -> GapSpec) -> GapMessage
ModifyGaps ((GapSpec -> GapSpec) -> GapMessage)
-> ((Direction2D -> Int -> Int) -> GapSpec -> GapSpec)
-> (Direction2D -> Int -> Int)
-> GapMessage
forall b c a. (b -> c) -> (a -> b) -> a -> c
. (Direction2D -> Int -> Int) -> GapSpec -> GapSpec
weakToStrong

-- | Arbitrarily modify a single gap with the given function.
modifyGap :: (Int -> Int) -> Direction2D -> GapMessage
modifyGap :: (Int -> Int) -> Direction2D -> GapMessage
modifyGap Int -> Int
f Direction2D
d = (GapSpec -> GapSpec) -> GapMessage
ModifyGaps ((GapSpec -> GapSpec) -> GapMessage)
-> (GapSpec -> GapSpec) -> GapMessage
forall a b. (a -> b) -> a -> b
$ (Int -> Int) -> Direction2D -> GapSpec -> GapSpec
continuation Int -> Int
f Direction2D
d

-- | Set the GapSpec.
setGaps :: GapSpec -> GapMessage
setGaps :: GapSpec -> GapMessage
setGaps = (GapSpec -> GapSpec) -> GapMessage
ModifyGaps ((GapSpec -> GapSpec) -> GapMessage)
-> (GapSpec -> GapSpec -> GapSpec) -> GapSpec -> GapMessage
forall b c a. (b -> c) -> (a -> b) -> a -> c
. GapSpec -> GapSpec -> GapSpec
forall a b. a -> b -> a
const

-- | Set a gap to the given value.
setGap :: Int -> Direction2D -> GapMessage
setGap :: Int -> Direction2D -> GapMessage
setGap = (Int -> Int) -> Direction2D -> GapMessage
modifyGap ((Int -> Int) -> Direction2D -> GapMessage)
-> (Int -> Int -> Int) -> Int -> Direction2D -> GapMessage
forall b c a. (b -> c) -> (a -> b) -> a -> c
. Int -> Int -> Int
forall a b. a -> b -> a
const

-- | Imposes limits upon a GapSpec, ensuring gaps are at least 0. Not exposed.
limit :: GapSpec -> GapSpec
limit :: GapSpec -> GapSpec
limit = (Direction2D -> Int -> Int) -> GapSpec -> GapSpec
weakToStrong ((Direction2D -> Int -> Int) -> GapSpec -> GapSpec)
-> (Direction2D -> Int -> Int) -> GapSpec -> GapSpec
forall a b. (a -> b) -> a -> b
$ \Direction2D
_ -> Int -> Int -> Int
forall a. Ord a => a -> a -> a
max Int
0

-- | Takes a weak gaps-modifying function f and returns a GapSpec modifying
-- function. Not exposed.
weakToStrong :: (Direction2D -> Int -> Int) -> GapSpec -> GapSpec
weakToStrong :: (Direction2D -> Int -> Int) -> GapSpec -> GapSpec
weakToStrong Direction2D -> Int -> Int
f GapSpec
gs = [Direction2D] -> [Int] -> GapSpec
forall a b. [a] -> [b] -> [(a, b)]
zip (((Direction2D, Int) -> Direction2D) -> GapSpec -> [Direction2D]
forall a b. (a -> b) -> [a] -> [b]
map (Direction2D, Int) -> Direction2D
forall a b. (a, b) -> a
fst GapSpec
gs) (((Direction2D, Int) -> Int) -> GapSpec -> [Int]
forall a b. (a -> b) -> [a] -> [b]
map ((Direction2D -> Int -> Int) -> (Direction2D, Int) -> Int
forall a b c. (a -> b -> c) -> (a, b) -> c
uncurry Direction2D -> Int -> Int
f) GapSpec
gs)

-- | Given f as a definition for the behaviour of a gaps modifying function in
-- one direction d, produces a continuation of the function to the other
-- directions using the identity. Not exposed.
continuation :: (Int -> Int) -> Direction2D -> GapSpec -> GapSpec
continuation :: (Int -> Int) -> Direction2D -> GapSpec -> GapSpec
continuation Int -> Int
f Direction2D
d1 = (Direction2D -> Int -> Int) -> GapSpec -> GapSpec
weakToStrong Direction2D -> Int -> Int
h
  where h :: Direction2D -> Int -> Int
h Direction2D
d2 | Direction2D
d2 Direction2D -> Direction2D -> Bool
forall a. Eq a => a -> a -> Bool
== Direction2D
d1  = Int -> Int
f
             | Bool
otherwise = Int -> Int
forall a. a -> a
id

applyGaps :: Gaps a -> Rectangle -> Rectangle
applyGaps :: forall a. Gaps a -> Rectangle -> Rectangle
applyGaps Gaps a
gs Rectangle
r = ((Direction2D, Int) -> Rectangle -> Rectangle)
-> Rectangle -> GapSpec -> Rectangle
forall (t :: * -> *) a b.
Foldable t =>
(a -> b -> b) -> b -> t a -> b
foldr (Direction2D, Int) -> Rectangle -> Rectangle
forall {a}.
Integral a =>
(Direction2D, a) -> Rectangle -> Rectangle
applyGap Rectangle
r (Gaps a -> GapSpec
forall a. Gaps a -> GapSpec
activeGaps Gaps a
gs)
  where
    applyGap :: (Direction2D, a) -> Rectangle -> Rectangle
applyGap (Direction2D
U,a
z) (Rectangle Position
x Position
y Dimension
w Dimension
h) = Position -> Position -> Dimension -> Dimension -> Rectangle
Rectangle Position
x (Position
y Position -> Position -> Position
forall a. Num a => a -> a -> a
+ a -> Position
forall a b. (Integral a, Num b) => a -> b
fi a
z) Dimension
w (Dimension
h Dimension -> Dimension -> Dimension
forall a. Num a => a -> a -> a
- a -> Dimension
forall a b. (Integral a, Num b) => a -> b
fi a
z)
    applyGap (Direction2D
D,a
z) (Rectangle Position
x Position
y Dimension
w Dimension
h) = Position -> Position -> Dimension -> Dimension -> Rectangle
Rectangle Position
x Position
y Dimension
w (Dimension
h Dimension -> Dimension -> Dimension
forall a. Num a => a -> a -> a
- a -> Dimension
forall a b. (Integral a, Num b) => a -> b
fi a
z)
    applyGap (Direction2D
L,a
z) (Rectangle Position
x Position
y Dimension
w Dimension
h) = Position -> Position -> Dimension -> Dimension -> Rectangle
Rectangle (Position
x Position -> Position -> Position
forall a. Num a => a -> a -> a
+ a -> Position
forall a b. (Integral a, Num b) => a -> b
fi a
z) Position
y (Dimension
w Dimension -> Dimension -> Dimension
forall a. Num a => a -> a -> a
- a -> Dimension
forall a b. (Integral a, Num b) => a -> b
fi a
z) Dimension
h
    applyGap (Direction2D
R,a
z) (Rectangle Position
x Position
y Dimension
w Dimension
h) = Position -> Position -> Dimension -> Dimension -> Rectangle
Rectangle Position
x Position
y (Dimension
w Dimension -> Dimension -> Dimension
forall a. Num a => a -> a -> a
- a -> Dimension
forall a b. (Integral a, Num b) => a -> b
fi a
z) Dimension
h

activeGaps :: Gaps a -> GapSpec
activeGaps :: forall a. Gaps a -> GapSpec
activeGaps (Gaps GapSpec
conf [Direction2D]
cur) = ((Direction2D, Int) -> Bool) -> GapSpec -> GapSpec
forall a. (a -> Bool) -> [a] -> [a]
filter ((Direction2D -> [Direction2D] -> Bool
forall (t :: * -> *) a. (Foldable t, Eq a) => a -> t a -> Bool
`elem` [Direction2D]
cur) (Direction2D -> Bool)
-> ((Direction2D, Int) -> Direction2D)
-> (Direction2D, Int)
-> Bool
forall b c a. (b -> c) -> (a -> b) -> a -> c
. (Direction2D, Int) -> Direction2D
forall a b. (a, b) -> a
fst) GapSpec
conf

toggleGaps :: GapSpec -> [Direction2D] -> [Direction2D]
toggleGaps :: GapSpec -> [Direction2D] -> [Direction2D]
toggleGaps GapSpec
conf [] = ((Direction2D, Int) -> Direction2D) -> GapSpec -> [Direction2D]
forall a b. (a -> b) -> [a] -> [b]
map (Direction2D, Int) -> Direction2D
forall a b. (a, b) -> a
fst GapSpec
conf
toggleGaps GapSpec
_    [Direction2D]
_  = []

toggleGap :: GapSpec -> [Direction2D] -> Direction2D -> [Direction2D]
toggleGap :: GapSpec -> [Direction2D] -> Direction2D -> [Direction2D]
toggleGap GapSpec
conf [Direction2D]
cur Direction2D
d | Direction2D
d Direction2D -> [Direction2D] -> Bool
forall (t :: * -> *) a. (Foldable t, Eq a) => a -> t a -> Bool
`elem` [Direction2D]
cur            = Direction2D -> [Direction2D] -> [Direction2D]
forall a. Eq a => a -> [a] -> [a]
delete Direction2D
d [Direction2D]
cur
                     | Direction2D
d Direction2D -> [Direction2D] -> Bool
forall (t :: * -> *) a. (Foldable t, Eq a) => a -> t a -> Bool
`elem` ((Direction2D, Int) -> Direction2D) -> GapSpec -> [Direction2D]
forall a b. (a -> b) -> [a] -> [b]
map (Direction2D, Int) -> Direction2D
forall a b. (a, b) -> a
fst GapSpec
conf = Direction2D
dDirection2D -> [Direction2D] -> [Direction2D]
forall a. a -> [a] -> [a]
:[Direction2D]
cur
                     | Bool
otherwise               = [Direction2D]
cur

-- | Add togglable manual gaps to a layout.
gaps :: GapSpec   -- ^ The gaps to allow, paired with their initial sizes.
     -> l a       -- ^ The layout to modify.
     -> ModifiedLayout Gaps l a
gaps :: forall (l :: * -> *) a. GapSpec -> l a -> ModifiedLayout Gaps l a
gaps GapSpec
g = Gaps a -> l a -> ModifiedLayout Gaps l a
forall (m :: * -> *) (l :: * -> *) a.
m a -> l a -> ModifiedLayout m l a
ModifiedLayout (GapSpec -> [Direction2D] -> Gaps a
forall a. GapSpec -> [Direction2D] -> Gaps a
Gaps GapSpec
g (((Direction2D, Int) -> Direction2D) -> GapSpec -> [Direction2D]
forall a b. (a -> b) -> [a] -> [b]
map (Direction2D, Int) -> Direction2D
forall a b. (a, b) -> a
fst GapSpec
g))

-- | Add togglable manual gaps to a layout, explicitly specifying the initial states.
gaps' :: [((Direction2D,Int),Bool)] -- ^ The gaps to allow and their initial states.
      -> l a                        -- ^ The layout to modify.
      -> ModifiedLayout Gaps l a
gaps' :: forall (l :: * -> *) a.
[((Direction2D, Int), Bool)] -> l a -> ModifiedLayout Gaps l a
gaps' [((Direction2D, Int), Bool)]
g = Gaps a -> l a -> ModifiedLayout Gaps l a
forall (m :: * -> *) (l :: * -> *) a.
m a -> l a -> ModifiedLayout m l a
ModifiedLayout (GapSpec -> [Direction2D] -> Gaps a
forall a. GapSpec -> [Direction2D] -> Gaps a
Gaps ((((Direction2D, Int), Bool) -> (Direction2D, Int))
-> [((Direction2D, Int), Bool)] -> GapSpec
forall a b. (a -> b) -> [a] -> [b]
map ((Direction2D, Int), Bool) -> (Direction2D, Int)
forall a b. (a, b) -> a
fst [((Direction2D, Int), Bool)]
g) [Direction2D
d | ((Direction2D
d,Int
_),Bool
v) <- [((Direction2D, Int), Bool)]
g, Bool
v])