syntax puzzle

Whi do I get a syntax error

hendrik@notlookedfor:~/dv/lang/experiment/autometa$ ocamlc ko.ml -o ko
File "ko.ml", line 4, characters 10-11:
Error: Syntax error

for the following code:

hendrik@notlookedfor:~/dv/lang/experiment/autometa$ cat ko.ml

   type exp =
         (* type constructors *)
	 Pity of {source : exp; target : exp}
;;
hendrik@notlookedfor:~/dv/lang/experiment/autometa$ 

bot not: 

hendrik@notlookedfor:~/dv/lang/experiment/autometa$ ocamlc ok.ml -o ok
hendrik@notlookedfor:~/dv/lang/experiment/autometa$ 

for this code:?

hendrik@notlookedfor:~/dv/lang/experiment/autometa$ cat ok.ml

   type exp =
         (* type constructors *)
	 Pity of xxx
	 and xxx = {source : exp; target : exp}
;;
hendrik@notlookedfor:~/dv/lang/experiment/autometa$ 

Am I really required to have an actual name after the 'of'?  I haven't
noticed a restriction like that anywhere else in the language.

I suspect something else is going on, but I'm at a loss to know what.

-- hendrik