cps tweaks

[lambda.git] / cps_and_continuation_operators.mdwn

diff --git a/cps_and_continuation_operators.mdwn b/cps_and_continuation_operators.mdwn
index 258f722..e3fb42d 100644 (file)
--- 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
 
 
                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:
 
 
 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
 
 
 Callcc examples


@@ -481,7 +481,7 @@ To demonstrate the different adding order between Examples 4 and 5, we use `::`
            let u = shift (fun k -> k [1] >>= fun x -> unit (10 :: x))
            in u >>= fun x -> unit (100 :: x)
          ) in let w = v >>= fun x -> unit (1000 :: x)
            let u = shift (fun k -> k [1] >>= fun x -> unit (10 :: x))
            in u >>= fun x -> unit (100 :: x)
          ) in let w = v >>= fun x -> unit (1000 :: x)

-         in run0  w)
+         in run0  w);;

        - : int list = [1000; 10; 100; 1]
 
 
        - : int list = [1000; 10; 100; 1]
 
 


@@ -493,7 +493,23 @@ Example 6:
          (app (reset (app2 (op2 plus) (var ten)
            (shift (\k. (var k))))) (var one))
        
          (app (reset (app2 (op2 plus) (var ten)
            (shift (\k. (var k))))) (var one))
        

-       (* not sure if this example can be typed as-is in OCaml. We may need a sum-type *)
+       (* not sure if this example can be typed as-is in OCaml... this is the best I an do at the moment... *)
+
+       # type 'x either = Left of (int -> ('x,'x either) Continuation_monad.m) | Right of int;;
+       # Continuation_monad.(let v = reset (
+           shift (fun k -> unit (Left k)) >>= fun i -> unit (Right (10+i))
+         ) in let w = v >>= fun (Left k) ->
+             k 1 >>= fun (Right i) ->
+             unit (100+i)
+         in run0 w);;
+       - : int = 111
+
+<!--
+# type either = Left of (int -> either) | Right of int;;
+# let getleft e = match e with Left lft -> lft | Right _ -> failwith "not a Left";;
+# let getright e = match e with Right rt -> rt | Left _ -> failwith "not a Right";;
+# 100 + getright (let v = reset (fun p () -> Right (10 + shift p (fun k -> Left k))) in getleft v 1);;
+-->

 
 Example 7:
 
 
 Example 7: