Greetings from /tg/

Hi there /prague/. I wrote a few simple functions to visualize and calculate probabilities of dice. Though you might be interested; maybe you can tell me how I'm ``doing it wrong''.
import Data.Function
import Data.List

add1dY y = concatMap (\x-> map (+x) [1..y])
addXdY y 0 xDy = xDy
addXdY y x xDy = addXdY y (x-1) (add1dY y xDy)

combineXdY y x = toHistogram $ addXdY y (x-1) [1..y]

sumFreqs = foldr ((+).snd) 0

pGreaterHist histogram i = ((/) `on` fromInteger.sumFreqs) greaters histogram
    where greaters = dropWhile ((<= i).fst) histogram

pLessHist histogram i = ((/) `on` fromInteger.sumFreqs) lessers histogram
    where lessers = takeWhile ((< i).fst) histogram

toHistogram [] = []
toHistogram lst =
    toHistogram' (x,1) xs
    where (x:xs) = sort lst
          toHistogram' pair [] = [pair]
          toHistogram' (x1,n) (x2:xs) =
            if x1 == x2
            then toHistogram' (x1,n+1) xs
            else (x1,n) : (toHistogram' (x2,1) xs)

showHistogram :: [(Int, Int)] -> IO ()
showHistogram = foldr (\ (i,n) y -> (putStrLn ((reverse $ take n bars) ++ " " ++ (show i))) >> y) (return ())
    where bars = "|"++(cycle "-")

(car (cdr (eval (apply))))