module Data.ANN.BAM
(BAM
,makeBAM
,recallForward
,recallBackward
) where

import Data.List

-- Discrete Bidirectional Associative Memory

-- Stores associations between pairs of vectors

-- Quick and dirty version using lists. Would be nice to do this using a vector space library

type Vector a = [a]
type Matrix a = [Vector a]

vecPlus = zipWith (+)
matPlus = zipWith vecPlus

matZero = repeat (repeat 0)
matProd xs ys = [ [sum $ zipWith (*) x y | y<-transpose ys] | x<-xs]

outerProd xs ys = [ [x*y | y<-ys] | x<-xs]

boolToInt b = if b then 1 else -1
intToBool i
    | i >= 0    = True
    | otherwise = False

sign i
    | i >= 0    = 1
    | otherwise = -1

data BAM = BAM (Matrix Int)
    deriving (Eq,Ord,Show)

makeBAM :: [(Vector Bool, Vector Bool)] -> BAM
makeBAM assocs = BAM $ foldl matPlus matZero [ (map boolToInt x) `outerProd` (map boolToInt y) | (x,y) <- assocs]

runBackward (BAM ws) y = [sign $ sum $ zipWith (*) w y | w<-ws]
runForward (BAM ws) x =  [sign $ sum $ zipWith (*) x w | w<-transpose ws]

recallForward bam x  = map intToBool $ untilStable (runForward bam . runBackward bam) $ map boolToInt x
recallBackward bam x = map intToBool $ untilStable (runBackward bam . runForward bam) $ map boolToInt x

untilStable f x = let x' = f x in if x==x' then x else untilStable f x'