Implement Closures and Partial Application

Unit 1/Lesson 5/closures.hs

@@ -0,0 +1,58 @@
+inc :: Num a => a -> a
+inc n = n + 1
+double :: Num a => a -> a
+double n = n * 2
+square :: Num a => a -> a
+square n = n ^ 2
+
+isEven :: Integral p => (p -> p) -> p -> p
+isEven f x = if even x
+             then f x
+             else x
+
+ifEvenInc :: Integer -> Integer
+ifEvenInc = isEven inc
+ifEvenDouble :: Integer -> Integer
+ifEvenDouble = isEven double
+ifEvenSquare :: Integer -> Integer
+ifEvenSquare = isEven square
+
+-- Generating URL's for an API
+
+getRequestURL :: [Char] -> [Char] -> [Char] -> [Char] -> [Char]
+getRequestURL host apiKey resource id = host ++ "/" ++
+                                        resource ++ "/" ++
+                                        id ++ "?token=" ++
+                                        apiKey
+
+genHostRequestBuilder :: [Char] -> [Char] -> [Char] -> [Char] -> [Char]
+genHostRequestBuilder host = (\apikey resource id -> getRequestURL host apikey resource id)
+genApiRequestBuilder :: (t1 -> t2 -> t3 -> t4) -> t1 -> t2 -> t3 -> t4
+genApiRequestBuilder hostBuilder apiKey = (\resource id -> hostBuilder apiKey resource id)
+genResourceRequestBuilder :: (t1 -> t2 -> t3 -> t4) -> t1 -> t2 -> t3 -> t4
+genResourceRequestBuilder hostBuilder apiKey resource = (\id -> hostBuilder apiKey resource id)
+
+exampleUrlBuilder :: [Char] -> [Char] -> [Char] -> [Char]
+exampleUrlBuilder = genHostRequestBuilder "http://example.com"
+myExampleUrlBuilder :: [Char] -> [Char] -> [Char]
+myExampleUrlBuilder = genApiRequestBuilder exampleUrlBuilder "1337hAsk3ll"
+myExampleResourceUrlBuilder :: [Char] -> [Char]
+myExampleResourceUrlBuilder = genResourceRequestBuilder exampleUrlBuilder "1337hAsk3ll" "books"
+
+-- Using Partial application
+
+exampleUrlBuilderPA :: [Char] -> [Char] -> [Char] -> [Char]
+exampleUrlBuilderPA = getRequestURL "http://example.com"
+myExampleUrlBuilderPA :: [Char] -> [Char] -> [Char]
+myExampleUrlBuilderPA = exampleUrlBuilderPA "1337hAsk3ll"
+myExampleResourceUrlBuilderPA :: [Char] -> [Char]
+myExampleResourceUrlBuilderPA = myExampleUrlBuilderPA "books"
+
+subtract2 :: Integer -> Integer
+subtract2 = flip (-) 2
+-- subtract2 x = flip (-) 2 x
+
+binaryPartialApplication :: (t1 -> t2 -> t3) -> t1 -> t2 -> t3
+binaryPartialApplication binaryFunc arg = (\x -> binaryFunc arg x)
+takeFrom4 :: Integer -> Integer
+takeFrom4 = binaryPartialApplication (-) 4