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clarified stop conditions for big-bang

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svn: r13867
This commit is contained in:
Matthias Felleisen 2009-02-27 03:11:00 +00:00
parent ba925a22d9
commit 3112bab011
1 changed files with 15 additions and 7 deletions
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22
collects/teachpack/2htdp/scribblings/universe.scrbl
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@ -91,10 +91,13 @@ The simplest kind of animated @tech{world} program is a time-based
@defproc[(run-simulation [create-image (-> natural-number/c scene)])
true]{
opens a canvas and starts a clock that tick 28 times per second.
Every time the clock ticks, DrScheme applies
@scheme[create-image] to the number of ticks passed since this function
call. The results of these applications are displayed in the canvas.
opens a canvas and starts a clock that tick 28 times per second. Every
time the clock ticks, DrScheme applies @scheme[create-image] to the
number of ticks passed since this function call. The results of these
function calls are displayed in the canvas. The simulation runs until you
click the @tt{Stop} button in DrScheme or close the window. At that
point, @scheme[run-simulation] returns the number of ticks that have
passed.
}
Example:
@ -183,7 +186,11 @@ The design of a world program demands that you come up with a data
itself as a scene; when the program must shut down; where to register the
world with a universe; and whether to record the stream of events. A world
specification may not contain more than one @scheme[on-tick],
@scheme[on-draw], or @scheme[register] clause.}
@scheme[on-draw], or @scheme[register] clause. A @scheme[big-bang]
expression returns the last world when the stop condition is satisfied
(see below) or when the programmer clicks on the @tt{Stop} button or
closes the canvas.
}
@itemize[
@ -328,9 +335,10 @@ All @tech{MouseEvent}s are represented via symbols:
([last-world? (-> (unsyntax @tech{WorldState}) boolean?)])]{
tell DrScheme to call the @scheme[last-world?] function whenever the canvas is
drawn. If this call produces @scheme[true], the world program is shut
down. Specifically, the clock is stopped; no more
down. Specifically, the clock is stopped; no more
tick events, @tech{KeyEvent}s, or @tech{MouseEvent}s are forwarded to
the respective handlers.
the respective handlers. The @scheme[big-bang] expression returns this
last world.
}}
@item{