September 2017 Update

Task/Vector-products/Haskell/vector-products.hs

@@ -1,32 +1,53 @@
+import Data.Monoid ((<>))
+
 type Vector a = [a]
+
 type Scalar a = a
 
-a,b,c,d :: Vector Int
-a = [ 3,  4,  5 ]
-b = [ 4,  3,  5 ]
-c = [-5,-12,-13 ]
-d = [ 3,  4,  5,  6 ]
+a, b, c, d :: Vector Int
+a = [3, 4, 5]
 
-dot :: (Num t) => Vector t -> Vector t -> Scalar t
-dot u v | length u == length v = sum $ zipWith (*) u v
-        | otherwise = error "Dotted Vectors must be of equal dimension."
+b = [4, 3, 5]
 
-cross :: (Num t) => Vector t -> Vector t -> Vector t
-cross u v | length u == 3 && length v == 3 =
-             [u !! 1 * v !! 2 - u !! 2 * v !! 1,
-              u !! 2 * v !! 0 - u !! 0 * v !! 2,
-              u !! 0 * v !! 1 - u !! 1 * v !! 0]
-          | otherwise = error "Crossed Vectors must both be three dimensional."
+c = [-5, -12, -13]
 
-scalarTriple :: (Num t) => Vector t -> Vector t -> Vector t -> Scalar t
+d = [3, 4, 5, 6]
+
+dot
+  :: (Num t)
+  => Vector t -> Vector t -> Scalar t
+dot u v
+  | length u == length v = sum $ zipWith (*) u v
+  | otherwise = error "Dotted Vectors must be of equal dimension."
+
+cross
+  :: (Num t)
+  => Vector t -> Vector t -> Vector t
+cross u v
+  | length u == 3 && length v == 3 =
+    [ u !! 1 * v !! 2 - u !! 2 * v !! 1
+    , u !! 2 * head v - head u * v !! 2
+    , head u * v !! 1 - u !! 1 * head v
+    ]
+  | otherwise = error "Crossed Vectors must both be three dimensional."
+
+scalarTriple
+  :: (Num t)
+  => Vector t -> Vector t -> Vector t -> Scalar t
 scalarTriple q r s = dot q $ cross r s
 
-vectorTriple :: (Num t) => Vector t -> Vector t -> Vector t -> Vector t
+vectorTriple
+  :: (Num t)
+  => Vector t -> Vector t -> Vector t -> Vector t
 vectorTriple q r s = cross q $ cross r s
 
-main = do
-   mapM_ putStrLn [ "a . b     = " ++ (show $ dot a b)
-                  , "a x b     = " ++ (show $ cross a b)
-                  , "a . b x c = " ++ (show $ scalarTriple a b c)
-                  , "a x b x c = " ++ (show $ vectorTriple a b c)
-                  , "a . d     = " ++ (show $ dot a d) ]
+main :: IO ()
+main =
+  mapM_
+    putStrLn
+    [ "a . b     = " <> show (dot a b)
+    , "a x b     = " <> show (cross a b)
+    , "a . b x c = " <> show (scalarTriple a b c)
+    , "a x b x c = " <> show (vectorTriple a b c)
+    , "a . d     = " <> show (dot a d)
+    ]