Further improve the pretty printing and add some test cases in part2.cd

tests/poly/part2.cd

@@ -42,6 +42,8 @@ let balance ( Unbal ->Rtree ; ('b \ Unbal) ->('b \ Unbal) )
   | x -> x
 ;;
 
+let f (_ : ('a | 'b | 'c)) (_ : (Int&'d&'e \1--3 )) : Any = raise "123";;
+
 let balance (Unbal ->Rtree ;  'a -> 'a )
   | <blk (z)>[ <red (y)>[ <red (x)>[ a b ] c ] d ]
   | <blk (z)>[ <red (x)>[ a <red (y)>[ b c ] ] d ]