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docs for keyevent

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svn: r10596
This commit is contained in:
Matthias Felleisen 2008-07-04 14:25:28 +00:00
parent 1e30f69c6c
commit 5030202099
1 changed files with 12 additions and 7 deletions
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19
collects/teachpack/htdp/scribblings/world.scrbl
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@ -116,7 +116,13 @@ A @tech{KeyEvent} represents key board events, e.g., keys pressed or
@scheme['release] denote arrow keys or special events, such as releasing
the key on the keypad.
@defproc[(on-key-event [change (-> (unsyntax @tech{World}) (unsyntax @tech{KeyEvent}) (unsyntax @tech{World}))]) true]{
@defproc[(key-event? [x any]) boolean?]{
is @scheme[x] a @tech{KeyEvent}}
@defproc[(ke=? [x key-event?][y key-event?]) boolean?]{
compares two @tech{KeyEvent} for equality}
@defproc[(on-key-event [change (-> (unsyntax @tech{World}) key-event? (unsyntax @tech{World}))]) true]{
Tell DrScheme to call @scheme[change] on the current world and a
@tech{KeyEvent} for every keystroke the user of the computer makes. The result
of the call becomes the current world.
@ -127,12 +133,11 @@ A @tech{KeyEvent} represents key board events, e.g., keys pressed or
(schemeblock
(define (change w a-key-event)
(cond
[(char? a-key-event) w]
;; else (symbol? a-key-event) holds
[(symbol=? a-key-event 'left) (world-go w -DELTA)]
[(symbol=? a-key-event 'right) (world-go w +DELTA)]
[(symbol=? a-key-event 'up) (world-go w -DELTA)]
[(symbol=? a-key-event 'down) (world-go w +DELTA)]
[(ke=? a-key-event 'left) (world-go w -DELTA)]
[(ke=? a-key-event 'right) (world-go w +DELTA)]
[(char? a-key-event) w] ;; to demonstrate order-free checking
[(ke=? a-key-event 'up) (world-go w -DELTA)]
[(ke=? a-key-event 'down) (world-go w +DELTA)]
[else w]))
))