decodeBinaryDigits.hs

-- ff is our foldingfunction
-- (c,s) is the accumulator argument, which consists of an Int and a String
-- c accumulates bits when 0 or 1 is encountered
-- when 8 bits are accumulated, they are prepended to the string s
-- ch is the next character being passed from fold.
ff (c,s) ch = 
    if ch=='0' || ch=='1' then
        let c2=c*2+(fromEnum ch - 48) in
        if c2>255 then (1,toEnum(c2-256):s) 
                  else (c2,s)
    else (c,s)

decbin = reverse . snd . foldl ff (1,"") 

main = do
    putStrLn "Enter some binary digits to decode into ASCII:"
    ln <- getLine
    putStrLn $ decbin ln