You can use equirecursive types, which can be enabled through the
-rectypes command-line switch. With that option, your example above
type-checks. However, these are not enabled by default for a variety of
reasons, the most important one being it makes it much easier to shoot
yourself in the foot.
Cheers,
jonathan
On Sat 10 Sep 2011 01:14:46 AM CEST, Anthony Tavener wrote:
I was considering returning a couple of closures to help organize my
UI code, essentially representing current UI mode by one of these
closures. But then I run into a problem because the types are infinite
(returns a function, which returns a function, ...)
A simplified example:
# let rec a () = printf "state a\n"; b
and b () = printf "state b\n"; a
Error: This expression has type unit -> unit -> 'a
but an expression was expected of type 'a
Is there a way I can do this? To express (or 'hide') the cyclic nature
of the type resolution?
I've considered using continuations, but that seems heavy-weight for
what I'm looking to do. And as far as I can tell I'd need to leverage
Oleg's delimcc (which I'd love to start using and wrap my head around
-- but for a task worthy of it!).
I can use a variant to represent states/modes and have a dispatcher
which runs the right code... but this introduces what feels like an
unnecessary layer of distraction. Returning the closure of the "next
state" seems straightforward, but introduces cycles into the typing. :(
I'm hoping I'm missing something simple. Thank-you for any assistance!
-Tony
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