added prefab structs to messages that universe can exchange

collects/2htdp/private/check-aux.rkt

@@ -26,7 +26,7 @@
 ;                                                                               
 ;                                                                               
 
-;; -----------------------------------------------------------------------------
+;; ---------------------------------------------------------------------------------------------------
 
 ;; Any -> Boolean
 (define (nat? x)
@@ -37,14 +37,14 @@
   (check-arg t (and (number? x) (real? x)) "real number" p x)
   (inexact->exact (floor x)))
 
-;; -----------------------------------------------------------------------------
+;; ---------------------------------------------------------------------------------------------------
 ;; Nat Nat ->String 
 ;; converts i to a string, adding leading zeros, make it at least as long as L
 (define (zero-fill i L)
   (let ([n (number->string i)])
     (string-append (make-string (max (- L (string-length n)) 0) #\0) n)))
 
-;; -----------------------------------------------------------------------------
+;; ---------------------------------------------------------------------------------------------------
 
 ;; MouseEvent% -> [List Nat Nat MouseEventType]
 ;; turn a mouse event into its pieces 
@@ -78,13 +78,13 @@
     [(symbol? x) (symbol->string x)]
     [else (error 'on-key (format "Unknown event: ~a" x))]))
 
-;; -----------------------------------------------------------------------------
+;; ---------------------------------------------------------------------------------------------------
 ;; Any -> Symbol 
 (define (name-of draw tag)
   (define fname  (object-name draw))
   (if fname fname tag))
 
-;; -----------------------------------------------------------------------------
+;; ---------------------------------------------------------------------------------------------------
 ;; Any -> Boolean
 (define (sexp? x)
   (cond
@@ -95,12 +95,18 @@
     [(boolean? x) true]
     [(char? x) true]
     [(pair? x) (and (list? x) (andmap sexp? x))]
+    [(and (struct? x) (prefab-struct-key x)) (for/and ((i (struct->vector x))) (sexp? i))]
     [else false]))
 
+; tests:
+;(struct s (t) #:prefab)
+;(unless (sexp? (list (s (list 'a))))
+;  (error 'prefab "structs should be sexp?"))
+
 (define (no-newline? x)
   (not (member #\newline (string->list x))))
 
-;; -----------------------------------------------------------------------------
+;; ---------------------------------------------------------------------------------------------------
 ;; exchange one-line messages between worlds and the server
 
 (define tcp-eof (gensym 'tcp-eof))

collects/2htdp/tests/struct-universe.rkt

@@ -0,0 +1,46 @@
+#lang racket/load
+
+(module shared racket/base
+  (require 2htdp/universe 2htdp/image)
+  
+  (struct s (t) #:prefab)
+  (provide s s-t (all-from-out 2htdp/universe 2htdp/image)))
+
+(module client racket
+  (require 'shared)
+
+  ;; Color -> Boolean 
+  (define (client c)
+    (define count 0)
+    (big-bang #true
+              (to-draw (lambda (w) (text (if w "hello world" "good bye") 22 c)))
+              (register LOCALHOST)
+              (stop-when (lambda (w) (> count 3)))
+              (on-receive 
+               (lambda (w msg)
+                 (set! count (+ count 1))
+                 ;; send out a prefabed struct to the server 
+                 (make-package (not w) (s count)))))) 
+  
+  (launch-many-worlds (client 'blue) (client 'red)))
+
+(module server racket 
+  (require 'shared)
+  
+  (define (server)
+    (universe '()
+              (on-new (lambda (w n) (make-bundle (cons n w) '() '())))
+              (on-tick
+               (lambda (w*)
+                 (make-bundle w* (map (lambda (w) (make-mail w 'go)) w*) '())))
+              (on-msg 
+               (lambda (state iw msg)
+                 ;; display the received prefabbed struct's content 
+                 (displayln (s-t msg))
+                 (make-bundle state '() '())))))
+  
+  (thread server))
+
+(require 'server)
+
+(require 'client)

collects/2htdp/xtest

@@ -36,4 +36,5 @@ run stop-when-crash.rkt
 run on-tick-universe-with-limit.rkt
 run on-tick-with-limit.rkt
 run on-release-no-key.rkt
+run struct-universe.rkt
 

collects/teachpack/2htdp/scribblings/universe.scrbl

@@ -692,9 +692,10 @@ data; to be precise, an S-expression is one of:
  @item{a number,}
  @item{a boolean,}
  @item{a char, or}
- @item{a list of S-expressions.}
+ @item{a list of S-expressions, or}
+ @item{a prefab struct of S-expressions.}
 ]
-Note the last clause includes @racket[empty] of course. 
+Note the @racket[list] clause includes @racket[empty] of course. 
 
 @defproc[(sexp? [x any/c]) boolean?]{
  determines whether @racket[x] is an @tech{S-expression}.}
@@ -734,7 +735,7 @@ As mentioned, all event handlers may return @tech{WorldState}s or
 }
 
 @defform/none[#:literals (on-tick)
-              (on-tick tick-expr rate-expr)
+              (on-tick tick-expr rate-expr limit-expr)
               #:contracts
               ([tick-expr (-> (unsyntax @tech{WorldState}) (or/c (unsyntax @tech{WorldState}) package?))]
                [rate-expr (and/c real? positive?)]