Data commit

Task/ISBN13-check-digit/Haskell/isbn13-check-digit-1.hs

@@ -0,0 +1,28 @@
+import Data.Char (digitToInt, isDigit)
+import Text.Printf (printf)
+
+pair :: Num a => [a] -> [(a, a)]
+pair [] = []
+pair xs = p (take 2 xs) : pair (drop 2 xs)
+  where
+    p ps = case ps of
+      (x : y : zs) -> (x, y)
+      (x : zs) -> (x, 0)
+
+validIsbn13 :: String -> Bool
+validIsbn13 isbn
+  | length (digits isbn) /= 13 = False
+  | otherwise = calc isbn `rem` 10 == 0
+  where
+    digits = map digitToInt . filter isDigit
+    calc = sum . map (\(x, y) -> x + y * 3) . pair . digits
+
+main :: IO ()
+main =
+  mapM_
+    (printf "%s: Valid: %s\n" <*> (show . validIsbn13))
+    [ "978-1734314502",
+      "978-1734314509",
+      "978-1788399081",
+      "978-1788399083"
+    ]

Task/ISBN13-check-digit/Haskell/isbn13-check-digit-2.hs

@@ -0,0 +1,20 @@
+import Data.Char (digitToInt, isDigit)
+
+isISBN13 :: String -> Bool
+isISBN13 =
+  (0 ==)
+    . flip rem 10
+    . sum
+    . flip
+      (zipWith ((*) . digitToInt) . filter isDigit)
+      (cycle [1, 3])
+
+main :: IO ()
+main =
+  mapM_
+    (print . ((,) <*> isISBN13))
+    [ "978-1734314502",
+      "978-1734314509",
+      "978-1788399081",
+      "978-1788399083"
+    ]