gistfile1.hs

data BFState = BFState {
    dataLeft :: [Word8], 
    dataRight :: [Word8], 
    codeLeft :: [Char], 
    codeRight :: [Char], 
    bfOutput :: [Char]
    }
    
fwdCode, backCode :: State BFState ()
fwdCode =  modify $ \s@(BFState{codeLeft=ls, codeRight=r:rs}) -> s{codeLeft=r:ls, codeRight=rs}
backCode = modify $ \s@(BFState{codeLeft=l:ls, codeRight=rs}) -> s{codeLeft=ls, codeRight=l:rs}

fwdData, backData :: State BFState ()
fwdData =  modify $ \s@(BFState{dataLeft=ls, dataRight=r:rs}) -> s{dataLeft=r:ls, dataRight=rs}
backData = modify $ \s@(BFState{dataLeft=l:ls, dataRight=rs}) -> s{dataLeft=ls, dataRight=l:rs}

runBF :: State BFState ()
runBF = do
    r <- running 
    if not r then return () else do
        stepBF
        runBF

stepBF :: State BFState ()
stepBF = do
    c <- currCode
    d <- getData
    fwdCode
    case c of 
        '+' -> incData
        '-' -> decData
        '>' -> fwdData
        '<' -> backData
        _ -> return ()