monads

haskell/sessions/16_03/scratchpad/a.hs

@@ -0,0 +1,62 @@
+z :: Int -> Int
+z a = 3 * a -- 3x3 = 9 => 3*3
+
+y :: (Int -> Int) -> [Int] -> [Int]
+-- y(\x -> 3*x) [1,2,3] -> [3,6,9]
+y z lst = map z lst -- f(x) = 3x => f x = 3x
+
+isEven :: Int -> Bool
+isEven x = if x `mod` 2 == 0 then True else False
+
+-- ~~mod(x, 2)~~ => x mod 2
+-- isEven x = x `mod` 2 == 0
+
+isAmongus :: String -> String
+-- traverse each character and check if "amongus" is in the string, return the rest of the string
+isAmongus [] = [] -- base case if the string is empty (or we reached the end of the string)
+isAmongus (x : xs) -- recurse on the rest of the string
+  | (take 7 (x : xs) == "amongus") = drop 7 (x : xs)
+  | otherwise = isAmongus xs
+
+b :: [Int] -> Int
+b lst = sum (y z lst) -- = 18
+
+allTogether :: [Int] -> Int
+allTogether list = sum (map (3 *) list)
+
+foo :: Integer -> Integer
+foo 0 = 16
+foo 1
+  | "Haskell" > "C++" = 3
+  | otherwise = 4
+foo n
+  | n < 0 = 0
+  | n `mod` 17 == 2 = -43
+  | otherwise = n + 3
+
+bogus :: [a] -> Bool
+bogus (x:_) = True
+bogus _     = False
+
+
+main :: IO ()
+main = do
+    print $ b [1, 2, 3]
+    putStrLn "AAAAAAAAA"
+    print $ allTogether [1, 2, 3]
+
+    putStrLn "Finding amongus"
+    print $ isAmongus "amongus"
+    print $ isAmongus "aaaaaaaaaaaaaa"
+    print $ isAmongus "askldhjewkjrhwekjrhwekjrhekjlfhbjerkshtjkernamogusejqwklwqhekqjwehqwjkamongusasdasdsad"
+
+--   foos
+    print $ foo 0
+
+    print $ bogus [1,10..]
+
+    -- compose 2 functions with a dot
+    print $ (y z . y z) [1, 2, 3]
+    print $ (y z . y z . y z) [1, 2, 3]
+    print $ (.) (y z) (y z) [1, 2, 3]
+    print $ y z $ y z [1, 2, 3]