General purpose library for undo/redo. Inspired by David Nolen's talk at Philly ETE.

History.elm

module History where

data Step a = Undo | Redo | Checkpoint a | NoCheckpoint a

foldp : (a -> b -> b) -> b -> Signal (Step a) -> Signal b

-- It could also be interesting to have custom strategies for keeping track
-- of history. Maybe you want to have a fixed size stack, infinite stack,
-- stack with exponential decay, etc.

foldpWith : History b -> (a -> b -> b) -> b -> Signal (Step a) -> Signal b

type History a =
  { undo : History a -> History a
  , redo : History a -> History a
  , add  : a -> History a -> History a
  }

finite : Int -> History a
finite n =
  { undo = ...
  , redo = ...
  , add  = ...
  }

infinite : History a

exponentialDecay : [(Int,Fidelity)] -> History a