[Xmonad] layout combinators

[Joe Thornber]

I'm not going to get time to look at this again until the weekend, so
I thought I'd post what I had for people to muse over.

Combining splitters rather than rectangles is a neat idea (I hope).
However I think we do need a combinator that merges rectangles back
together again.  Consider a layout consisting of three columns, where
the middle column is twice the width of the out ones.  To do this I'd
like to create four columns and then merge together the two middle
columns:

    eg, merge [1..2] . hcat . replicate 4 $ unit

I really don't like passing indexes to merge, so if anyone can come up
with a nicer way I'd be very interested.

For now, this approach ignores the whole issue of scaling factors
given by the user to get the window sizes exactly as they want.  But I
do wonder if that can be done as a seperate distortion pass over the
resultant rects anyway.

- Joe


    --
    -- Layout combinators
    --
    type Splitter = Rect -> [Rect]

    unit :: Splitter
    unit = (: [])

    catDir :: Direction -> [Splitter] -> Splitter
    catDir dir splitters = concat .
                           zipWith ($) splitters .
                           divideMany (length splitters) dir

    hcat, vcat :: [Splitter] -> Splitter

    hcat splitters = catDir East splitters
    vcat splitters = catDir South splitters

    hjoin, vjoin :: Splitter -> Splitter -> Splitter

    vjoin left right = vcat [left, right]
    hjoin left right = hcat [left, right]

    mkLayout :: (Int -> Splitter) -> Layout
    mkLayout s = Layout { doLayout = l, modifyLayout = const Nothing}
        where
          l sc ws = return . zip ws . map fromRect . s (length ws) . toRect $ sc

    --
    -- Layouts
    --
    ejtTall :: Layout
    ejtTall = mkLayout tall'
      where
        tall' 1 = unit
        tall' n = unit `hjoin` (vcat . replicate (n - 1) $ unit)

    ejtWide :: Layout
    ejtWide = mkLayout wide'
      where
        wide' 1 = unit
        wide' n = unit `vjoin` (hcat . replicate (n - 1) $ unit)

    ejtColumn :: Layout
    ejtColumn = mkLayout $ \_ -> hcat . replicate 4 $ (unit 'vjoin' unit)