day 3, add [un]curry and swap to utils

lib/utils.ml

@@ -9,3 +9,18 @@ let read_file name =
         | None -> close_in ic; acc in
     aux []
 
+module CS = Set.Make(Char);;
+
+let set_of_string str =
+    let rec aux s i st =
+        if i < 0 then st
+        else aux s (i - 1) (CS.add s.[i] st) in
+    aux str ((String.length str) - 1) CS.empty
+
+let map_pair f (a, b) = (f a, f b)
+
+let curry f x y = f (x, y)
+let uncurry f (x, y) = f x y
+let uncurry3 f (x, y, z) = f x y z
+
+let swap x y = y x