learning haskell

haskell-fiddling.hs

doubleMe x = x + x
doubleUs x y = doubleMe x + doubleMe y
doubleSmallNumber x = if   x < 100
                      then x * 2
                      else x

eoeo xs            = [if mod x 2 == 0 then 'e' else 'o' | x <- xs]
length'' xs        = sum [1 | _ <- xs]
combo xs ys        = [x ++ " " ++ y | x <- xs, y <- ys]
nestedEven xxs     = [[ x | x <- xs, even x] | xs <- xxs]
nestedEvenFlat xxs = [[x | x <- xs, even x ] | xs <- xxs]
maxEach  xs ys     = [ max (fst x) (snd x) | x <- zip xs ys]
maxEach' xs ys     = [ max a b | (a, b) <- zip xs ys]

foo :: (Integral a) => a -> String
foo 6      = "six"
foo _      = "other"

factorial :: (Integral a) => a -> a
factorial 0 = 1
factorial n = n * factorial (n - 1)

factorial' :: (Integral a) => a -> a
factorial' n
  | n == 0    = 1
  | otherwise = n * factorial (n - 1)

head' :: [a] -> a
head' [] = error "can't head an empty list!" 
head' (x:_) = x

length' :: [a] -> Int
length' []     = 0
length' (_:xs) = 1 + length' xs

capital :: String -> String
capital "" = ""
capital all@(x:_) = "The first letter of " ++ all ++ " is " ++ [x]

bmi :: (RealFloat a) => a -> a -> String
bmi w h
  | w / h ^ 2 <= 18.5 = "you're underweight"
  | w / h ^ 2 <= 25.0 = "you're normal"
  | w / h ^ 2 <= 30.0 = "you're fat"
  | otherwise         = "you're a whale"