Bjorklund.hs

module Sound.Tidal.Bjorklund (bjorklund) where

{-
    Bjorklund.hs - Euclidean patterns
    Copyright (C) 2006-2020, Rohan Drape and contributors

    This library is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This library is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this library.  If not, see <http://www.gnu.org/licenses/>.
-}

-- The below is taken from the hmt library. Tidal used to just include
-- the library but removed for now due to dependency problems.. We
-- could however likely benefit from other parts of the library..

type STEP a = ((Int, Int), ([[a]], [[a]]))

left :: STEP a -> STEP a
left ((i, j), (xs, ys)) =
  let (xs', xs'') = splitAt j xs
   in ((j, i - j), (zipWith (++) xs' ys, xs''))

right :: STEP a -> STEP a
right ((i, j), (xs, ys)) =
  let (ys', ys'') = splitAt i ys
   in ((i, j - i), (zipWith (++) xs ys', ys''))

bjorklund' :: STEP a -> STEP a
bjorklund' (n, x) =
  let (i, j) = n
   in if min i j <= 1
        then (n, x)
        else bjorklund' (if i > j then left (n, x) else right (n, x))

bjorklund :: (Int, Int) -> [Bool]
bjorklund (i, j') =
  let j = j' - i
      x = replicate i [True]
      y = replicate j [False]
      (_, (x', y')) = bjorklund' ((i, j), (x, y))
   in concat x' ++ concat y'