cps tweaks

Signed-off-by: Jim Pryor <profjim@jimpryor.net>

diff --git a/cps_and_continuation_operators.mdwn b/cps_and_continuation_operators.mdwn
index e3fb42d..b1f6c69 100644 (file)
--- a/cps_and_continuation_operators.mdwn
+++ b/cps_and_continuation_operators.mdwn
@@ -268,11 +268,13 @@ That won't work because `k 1` doesn't have type `int`, but we're trying to add i
 
 This also works and as you can see, delivers the expected answer `101`.
 
-At the moment, I'm not able to get the third example working with the monadic library. I thought that this should do it, but it doesn't type-check:
+The third example is more difficult to make work with the monadic library, because its types are tricky. I was able to get this to work, which uses OCaml's "polymorphic variants." These are generally more relaxed about typing. There may be a version that works with regular OCaml types, but I haven't yet been able to identify it. Here's what does work:
 
-       # C.(run0 (callcc (fun k -> unit (1,k)) >>= fun (p1,p2) -> p2 (2,unit) >>= fun p2' -> unit (p1,p2')));;
+       # C.(run0 (callcc (fun k -> unit (1,`Box k)) >>= fun (p1,`Box p2) -> p2 (2,`Box unit) >>= fun p2' -> unit (p1,p2')));;
+       - : int * (int * [ `Box of 'b -> ('a, 'b) C.m ] as 'b) as 'a =
+(2, (2, `Box <fun>))
 
-If we figure this out later (or anyone else does), we'll come back and report. <!-- FIXME -->
+<!-- FIXME -->