Remove shadowed names in documentation

docs/source/tutorial/typesfuns.rst

@@ -1350,7 +1350,7 @@ character:
 
     splitAt : Char -> String -> (String, String)
     splitAt c x = case break (== c) x of
-                      (x, y) => (x, strTail y)
+                      (l, r) => (l, strTail r)
 
 ``break`` is a library function which breaks a string into a pair of
 strings at the point where the given function returns true. We then