X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=blobdiff_plain;f=cps_and_continuation_operators.mdwn;h=63a40a16d50054136b5ae97e28c9f02713f97cec;hp=2063ef0eb4e08113d6bef9a5f663de661a322bbe;hb=6ad86f1d6d3688a9d2b90e6439905e284037ab4d;hpb=51ee06f53535b62965d8f34dbc4ab2456afe73c5

diff --git a/cps_and_continuation_operators.mdwn b/cps_and_continuation_operators.mdwn
index 2063ef0e..63a40a16 100644
--- a/cps_and_continuation_operators.mdwn
+++ b/cps_and_continuation_operators.mdwn
@@ -330,13 +330,14 @@ Next, try to figure out what this function does:
 	                      [(null? l) (k 'notfound)]
 	                      [(eq? (car l) a) (cdr l)]
 	                      [(atom? (car l)) (cons (car l) (aux (cdr l) k))]
-	                      ; what happens when (car l) exists but isn't an atom?
-	                      [else (let ([car2 (let/cc k2 ; now what will happen when k2 is called?
-	                                          (aux (car l) k2))])
-	                              (cond
-	                                ; when will the following condition be met? what happens then?
-	                                [(eq? car2 'notfound) (cons (car l) (aux (cdr l) k))]
-	                                [else (cons car2 (cdr l))]))]))]
+	                      [else
+	                       ; what happens when (car l) exists but isn't an atom?
+	                       (let ([car2 (let/cc k2 ; now what will happen when k2 is called?
+	                                     (aux (car l) k2))])
+	                         (cond
+	                           ; when will the following condition be met? what happens then?
+	                           [(eq? car2 'notfound) (cons (car l) (aux (cdr l) k))]
+	                           [else (cons car2 (cdr l))]))]))]
 	             [lst2 (let/cc k1 ; now what will happen when k1 is called?
 	                     (aux lst k1))])
 	      (cond
@@ -344,7 +345,6 @@ Next, try to figure out what this function does:
 	        [(eq? lst2 'notfound) lst]
 	        [else lst2]))))
 
-
 Here is [the answer](/hints/cps_hint_3), but try to figure it out for yourself.
 
 Here is the hardest example. Try to figure out what this function does:
@@ -397,7 +397,11 @@ Here is [the answer](/hints/cps_hint_4), but again, first try to figure it out f
 Delimited control operators
 ===========================
 
-`callcc` is what's known as an *undelimited control operator*. That is, the continuations `outk` that get bound to our `k`s behave as though they include all the code from the `call/cc ...` out to *and including* the end of the program.
+Here again is the CPS for `callcc`:
+
+ 	[callcc (\k. body)] = \outk. (\k. [body] outk) (\v localk. outk v)
+
+`callcc` is what's known as an *undelimited control operator*. That is, the continuations `outk` that get bound into our `k`s include all the code from the `call/cc ...` out to *and including* the end of the program. Calling such a continuation will never return any value to the call site. (See the technique employed in the `delta` example above, with the `(begin (let/cc k2 ...) ...)`, for a work-around.)
 
 Often times it's more useful to use a different pattern, where we instead capture only the code from the invocation of our control operator out to a certain boundary, not including the end of the program. These are called *delimited control operators*. A variety of the latter have been formulated.