Hello,

Alain Frisch wrote:
> Cyclic (aka recursive) types are necessary to type such an expression:
> # fun x -> x # run (); x;;
> - : (< run : unit -> 'b; .. > as 'a) -> 'a = <fun>

This is slightly misleading. Such a type is really non-recursive, since
it is an abbreviation for the following:

  < run : unit -> 'b; 'c > -> < run : unit -> 'b; 'c >

The notation (t as 'a) allows sharing relationships to appear explicitly
in print, yielding shorter and more readable types. It actually describes
a recursive type only when 'a occurs within t, which is not the case in
the example above. It happens e.g. when x is passed as a parameter to
one of its own methods:

  # fun x -> x#compare(x);;
  - : (< compare : 'a -> 'b; .. > as 'a) -> 'b = <fun>

-- 
François Pottier
Francois.Pottier@inria.fr
http://pauillac.inria.fr/~fpottier/
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