Haskell - lecture 7

-- isLower, isUpper etc. are not recognized in WinHugs if the prompt says "Main>" (but it is recognized on startup when the prompt is "Prelude>")
kindOfChar :: Char -> String
kindOfChar c =
 if (isLower c)
 then "lower"
 else if isUpper c
   then "upper"
   else if isDigit c
     then "digit"
     else "other"
-- Same function implemented with guards:
kindOfChar2 :: Char -> String
kindOfChar2 c    -- Notice that there is no "=" before the guards
 | isLower c = "lower"
 | isUpper c = "upper"
 | isDigit c = "digit"
 | otherwise = "other"

-- Acts like the prelude (built-in) function 'take'
myTake :: Int -> [a] -> [a]
myTake 0 list = []
myTake m [] = []
myTake m x:xs =
 x : (myTake (m-1) xs)
-- Implementation using "case" expression
-- Internally, this is how Haskell resolves multiple function declarations?
myTake2 :: Int -> [a] -> [a]
myTake2 n list = case (n,list) of
 (0, list) -> []
 (n, []) -> []
 (n, x:xs) -> c : myTake2 (n-1)

-- In Haskell
 -- Everything exists at the top level (mutually recursive (?))
 -- Basic libraries automatically exist in prelude
 -- Type synonym
 -- Type classes (Ord, Num, Fractional, ...)
 -- Read and Show
 -- Pattern findings