Fix.hs

module Filter.Fix where

import qualified Filter.Graph as Graph


{-|
A 'Graph.T' with numbered nodes is not very comfortable.
Better provide a 'Control.Monad.Fix.fix'-like function
which allows to enter a graph this way:

> fix $ \[v,w,y] ->
> [a·(u + d·w),
>  b·(v + e·y),
>  c· w]

-}

type T filter t a v  =
   [Channel filter t a v] -> [[(Channel filter t a v, filter t a v)]]

type ChannelId = Int

data Channel filter t a v =
   Channel {channelId     :: ChannelId,
            channelInputs :: [(ChannelId, filter t a v)]}


fix :: T filter t a v -> [Channel filter t a v]
fix f =
   let cs = zipWith (\n inputs ->
               Channel n (map (\(c,filt) -> (channelId c, filt)) inputs))
               [0 ..] (f cs)
   in  cs


toGraph :: T filter t a v -> Graph.T filter Int t a v
toGraph =
   Graph.fromList . map (\(Channel n inputs) -> (n, inputs)) . fix