Adding Haskell examples (#17)

* Adding binary search example for Haskell

* Adding selection sort example in Haskell

* Adding Haskell examples for chapter 3

* Adding examples for chapter 4

* Adding examples for chapter 5

* Adding git ignore

* Add Haskell example for BFS

05_hash_tables/Haskell/01_price_of_groceries.hs

@@ -0,0 +1,5 @@
+import qualified Data.HashMap.Strict as Map
+
+prices = Map.fromList [("Apple", 0.67), ("Milk", 1.49), ("Avocado", 1.55)]
+
+main = putStrLn (show (Map.lookup "Apple" prices))

05_hash_tables/Haskell/02_check_voter.hs

@@ -0,0 +1,17 @@
+import qualified Data.HashMap.Strict as Map
+
+all_voters = Map.fromList[("tom", True), ("mike", True)]
+
+check_voter name voters_map = case Map.lookup name voters_map of
+  Just _ -> ("kick them out!", voters_map)
+  otherwise -> ("let them vote!", Map.insert name True voters_map)
+
+log_vote name voters_map = do
+  putStrLn str
+  return new_voters_map
+  where (str, new_voters_map) = check_voter name voters_map
+
+main = do
+  try_mike <- log_vote "mike" all_voters
+  try_john <- log_vote "john" try_mike
+  return try_john