September 2017 Update

Task/Sort-an-array-of-composite-structures/Haskell/sort-an-array-of-composite-structures-1.hs

@@ -0,0 +1,26 @@
+import Data.List
+import Data.Function (on)
+
+data Person =
+  P String
+    Int
+  deriving (Eq)
+
+instance Show Person where
+  show (P name val) = "Person " ++ name ++ " with value " ++ show val
+
+instance Ord Person where
+  compare (P a _) (P b _) = compare a b
+
+pVal :: Person -> Int
+pVal (P _ x) = x
+
+people :: [Person]
+people = [P "Joe" 12, P "Bob" 8, P "Alice" 9, P "Harry" 2]
+
+
+main :: IO ()
+main = do
+  mapM_ print $ sort people
+  putStrLn []
+  mapM_ print $ sortBy (on compare pVal) people

Task/Sort-an-array-of-composite-structures/Haskell/sort-an-array-of-composite-structures-2.hs

@@ -0,0 +1,12 @@
+import Data.Ord (comparing)
+import Data.List (sortBy)
+
+xs :: [(String, String, Int)]
+xs =
+  zip3
+    (words "Richard John Marvin Alan Maurice James")
+    (words "Hamming McCarthy Minskey Perlis Wilkes Wilkinson")
+    [1915, 1927, 1926, 1922, 1913, 1919]
+
+main :: IO ()
+main = mapM_ print $ sortBy (comparing (\(_, _, y) -> y)) xs

Task/Sort-an-array-of-composite-structures/Haskell/sort-an-array-of-composite-structures.hs

@@ -1,11 +0,0 @@
-import List
-
-data Person = P String Int deriving Eq
-instance Show Person where
-    show (P name val) = "Person "++name++" with value "++(show val)
-instance Ord Person where
-    compare (P n1 _) (P n2 _) = compare n1 n2
-
-people = [(P "Joe" 12), (P "Bob" 8), (P "Alice" 9), (P "Harry" 2)]
-sortedPeople = sort people
-sortedPeopleByVal = sortBy (\(P _ v1) (P _ v2)->compare v1 v2) people