X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=blobdiff_plain;f=cps_and_continuation_operators.mdwn;h=2c3f35603d9110ed565013c45c68e1c8fb3e6f6c;hp=d1a85cf8e7fdd4fbf7de40cf8f769787d23fb862;hb=d406ca1da0d732706d6e9b13ed3cb06022e32735;hpb=6908f7726018f0d85c9c950033ffa77033ab24c1

diff --git a/cps_and_continuation_operators.mdwn b/cps_and_continuation_operators.mdwn
index d1a85cf8..2c3f3560 100644
--- a/cps_and_continuation_operators.mdwn
+++ b/cps_and_continuation_operators.mdwn
@@ -173,15 +173,15 @@ So too will examples. We'll give some examples, and show you how to try them out
 
 		let callcc body = fun outk -> body (fun v localk -> outk v) outk
 
-<!-- GOTCHAS?? -->
+	<!-- GOTCHAS?? -->
 
 3.	`callcc` was originally introduced in Scheme. There it's written `call/cc` and is an abbreviation of `call-with-current-continuation`. Instead of the somewhat bulky form:
 
-	(call/cc (lambda (k) ...))
+		(call/cc (lambda (k) ...))
 
-I prefer instead to use the lighter, and equivalent, shorthand:
+	I prefer instead to use the lighter, and equivalent, shorthand:
 
-	(let/cc k ...)
+		(let/cc k ...)
 
 
 Callcc examples
@@ -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 -->