cps tweak

[lambda.git] / cps_and_continuation_operators.mdwn

diff --git a/cps_and_continuation_operators.mdwn b/cps_and_continuation_operators.mdwn
index 0b0f25d..0d4eb1d 100644 (file)
--- a/cps_and_continuation_operators.mdwn
+++ b/cps_and_continuation_operators.mdwn
@@ -276,11 +276,14 @@ The third example is more difficult to make work with the monadic library, becau
 
 <!-- FIXME -->
 
+Some callcc/letcc exercises
+---------------------------
+
 Here are a series of examples from *The Seasoned Schemer*, which we recommended at the start of term. It's not necessary to have the book to follow the exercises, though if you do have it, its walkthroughs will give you useful assistance.
 
 For reminders about Scheme syntax, see [here](/assignment8/) and [here](/week1/) and [here](/translating_between_ocaml_scheme_and_haskell). Other resources are on our [[Learning Scheme]] page.
 
-All of the examples assume the following preface:
+Most of the examples assume the following preface:
 
        #lang racket
 
@@ -327,13 +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
@@ -341,7 +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: