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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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20
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)]) @defproc[(run-simulation [create-image (-> natural-number/c scene)])
true]{ true]{
opens a canvas and starts a clock that tick 28 times per second. opens a canvas and starts a clock that tick 28 times per second. Every
Every time the clock ticks, DrScheme applies time the clock ticks, DrScheme applies @scheme[create-image] to the
@scheme[create-image] to the number of ticks passed since this function number of ticks passed since this function call. The results of these
call. The results of these applications are displayed in the canvas. 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: 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 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 world with a universe; and whether to record the stream of events. A world
specification may not contain more than one @scheme[on-tick], 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[ @itemize[
@ -330,7 +337,8 @@ All @tech{MouseEvent}s are represented via symbols:
drawn. If this call produces @scheme[true], the world program is shut 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 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{ @item{