AulaRecursao

sumPositiveOnList [] = 0
sumPositiveOnList (x:xs) = (if x>0 then x else 0) + sumPositiveOnList xs

sumPositiveOnList' x = sum (filter (>0) x)

-- $ is for compose function and substitute the ( ),  example
-- f1 (f2 (5*x))
-- compose f1*f2 $ 5*x
-- f1*f2 $ 5 *x  , and for cutting $ sign for cutting

sumPositiveOnList2 x = sum $ filter (>0) x

--2
count :: Num p => (t -> Bool) -> [t] -> p
count _ [] = 0
count f (x:xs) = (if f x == True then 1 else 0) + count f xs

count' f (x:xs) = length $ filter f x -- or bracket way, without it , it's don't compile
--count f (x:xs) = length $ filter f x, says:  Multiple declarations of `count'

--3
num2 = do
 putStr "a = "
 a <- getLine
 putStr "b = "
 b <- getLine
 putStrLn $ "a+b = "++ a ++ "+" ++ b ++ "=" ++show((read a :: Double)+(read b::Double))

 --4
 --sn _ "" = ""
sN n s
 | n < 0 = "Invalid value of n"
 | n==0 = ""
 | otherwise = s ++ " " ++ sN (n-1) s

sns = do
 putStr "Give me a number n: "
 n <- getLine
 putStr "Type a string: "
 s <- getLine
 putStr $ sN (read n::Integer) s