structure Types =
struct

  type unique = unit ref

  datatype ty = 
            RECORD of (Symbol.symbol * ty) list * unique
          | NIL
          | INT
          | STRING
          | ARRAY of ty * unique
	  | NAME of Symbol.symbol * ty option ref
	  | UNIT

  fun joinstrs sep [] = ""
    | joinstrs sep l = foldr (fn (e, s) => s ^ sep ^ e) (hd l) (tl l)
	    
  fun name t =
      let fun namex (RECORD(bindings, unique), seen) =
		  (case List.find (fn x => x = RECORD(bindings,unique)) seen of
		       SOME x => "#1"
		     | NONE => "RECORD("
			       ^ (joinstrs ","
					(map (fn (name, ty) =>
						 (Symbol.name name) ^ ": "
						 ^ (namex (ty, [RECORD(bindings,unique)])))
					     bindings))
			       ^ ")")
	    | namex (NIL, seen) = "NIL"
	    | namex (INT, seen) = "INT"				  
	    | namex (STRING, seen) = "STRING"
	    | namex (ARRAY(ty, unique), seen) = ("ARRAY of " ^ (namex (ty, seen)))
	    | namex (NAME(sym, ref tyo), seen) =
	      (case tyo of (SOME x) => "NAME(" ^ (Symbol.name sym) ^ ") of " ^ (namex (x, x::seen))
			 | NONE => "NAME(" ^ (Symbol.name sym) ^ ") of NONE")
	    | namex (UNIT, seen) = "UNIT"
      in
	  namex(t,[])
      end
	    
  fun print t =
      let fun spc 0 = ()
	    | spc n = (TextIO.print " "; spc (n-1))
	  fun print_n (RECORD(bindings, unique), n) =
	      (spc n;
	       TextIO.print "RECORD(\n";
	       app (fn (name, binding) =>
		       (spc (n);
			TextIO.print ((Symbol.name name) ^ " ->\n");
			print_n(binding,n+1)))
		   bindings;
	       spc n;	       
	       TextIO.print ")\n")
	    | print_n (NIL, n) =
	      (spc n;
	       TextIO.print "NIL\n")
	    | print_n (INT, n) =
	      (spc n;
	       TextIO.print "INT\n")
	    | print_n (STRING,n) = 
	      (spc n;
	       TextIO.print "STRING\n")
	    | print_n (ARRAY(ty,unique), n) =
	      (spc n;
	       TextIO.print "ARRAY of\n";
	       print_n(ty,n+1))
	    | print_n (NAME(sym,oref), n) =
	      (spc n;
	       TextIO.print ("NAME = " ^ (Symbol.name sym) ^ " ->\n");
	       case oref of (ref (SOME x)) =>
			    (spc (n+1);
			     TextIO.print "SOME\n")
			  | (ref NONE) =>
			    (spc (n+1);
			     TextIO.print "NONE\n"))
	    | print_n (UNIT, n) = 
	      (spc n;
	       TextIO.print "UNIT\n")
      in
	  print_n(t,0)
      end
end