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warn programmers that the key event specification is incomplete; Closes PR13168

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This commit is contained in:
Matthias Felleisen 2012-12-26 17:23:51 -05:00
parent 1ad88436ff
commit a15ae19d46
1 changed files with 51 additions and 27 deletions
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78
collects/teachpack/2htdp/scribblings/universe.scrbl
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@ -1,6 +1,6 @@
#lang scribble/doc
@(require scribble/manual "shared.rkt"
@(require scribble/manual "shared.rkt" scribble/eval
(for-label scheme
(only-in lang/htdp-beginner check-expect)
teachpack/2htdp/universe
@ -288,27 +288,40 @@ The world ends when the clock has ticked more than @scheme[limit-expr] times.}}
For simplicity, we represent key events with strings, but not all strings
are key events. The representation of key events comes in distinct
classes. First, a single-character string is used to signal that the user
has hit a "regular" key. Some of these one-character strings may look
unusual:
has hit a "regular" key, such as
@itemize[
@item{@racket["q"] stands for the q key;}
@item{@racket["w"] stands for the w key;}
@item{@racket["e"] stands for the e key;}
@item{@racket["r"] stands for the r key; and so on.}
]
Some of these one-character strings look somewhat unusual:
@itemize[
@item{@racket[" "] stands for the space bar (@racket[#\space]);}
@item{@racket["\r"] stands for the return key (@racket[#\return]);}
@item{@racket["\r"] stands for the return and enter key (@racket[#\return]);}
@item{@racket["\t"] stands for the tab key (@racket[#\tab]); and}
@item{@racket["\b"] stands for the backspace key (@racket[#\backspace]).}
]
On rare occasions you may also encounter @racket["\u007F"], which is the
string representing the delete key (aka rubout).
Here is "proof" that these strings really have length 1:
@interaction[
(string-length "\t")
]
On rare occasions your programs may also encounter @racket["\u007F"],
which is the string representing the delete key (aka rubout).
Second, some keys have multiple-character string representations. Strings
with more than one character denote arrow keys or other special events,
starting with the most important:
starting with the four most important ones:
@itemize[
@item{@racket["left"] is the left arrow;}
@item{@racket["right"] is the right arrow;}
@item{@racket["up"] is the up arrow;}
@item{@racket["down"] is the down arrow;}
]
Here are some others that you may encounter:
@itemize[
@item{@racket["start"]}
@item{@racket["cancel"]}
@item{@racket["clear"]}
@ -330,24 +343,25 @@ Second, some keys have multiple-character string representations. Strings
@item{@racket["snapshot"]}
@item{@racket["insert"]}
@item{@racket["help"]}
@item{@racket["numpad0"],
@racket["numpad1"],
@racket["numpad2"],
@racket["numpad3"],
@racket["numpad4"],
@racket["numpad5"],
@racket["numpad6"],
@racket["numpad7"],
@racket["numpad8"],
@racket["numpad9"],
@racket["numpad-enter"],
@racket["multiply"],
@racket["add"],
@racket["separator"],
@racket["subtract"],
@racket["decimal"],
@racket["divide"]}
@item{@racket["f1"],
@;item{@racket["numpad0"],
@;racket["numpad1"],
@;racket["numpad2"],
@;racket["numpad3"],
@;racket["numpad4"],
@;racket["numpad5"],
@;racket["numpad6"],
@;racket["numpad7"],
@;racket["numpad8"],
@;racket["numpad9"],
@;racket["numpad-enter"],
@;racket["multiply"],
@;racket["add"],
@;racket["separator"],
@;racket["subtract"],
@;racket["decimal"],
@;racket["divide"]}
@item{function keys:
@racket["f1"],
@racket["f2"],
@racket["f3"],
@racket["f4"],
@ -372,12 +386,22 @@ Second, some keys have multiple-character string representations. Strings
@racket["f23"],
@racket["f24"]}
@item{@racket["numlock"]}
@item{@racket["scroll"]}
@item{@racket["scroll"]}]
The following four count as keyevents even though they are triggered by
physical events on some form of mouse:
@itemize[
@item{@racket["wheel-up"]}
@item{@racket["wheel-down"]}
@item{@racket["wheel-left"]}
@item{@racket["wheel-right"]}
]
The preceding enumeration is neither complete in covering all the events
that this library deals with nor does it specify which events the library
ignores. If you wish to design a program that relies on specific keys on
your keyboard, you should first write a small test program to find out
whether the chosen keystrokes are caught by the library and, if so, which
string representations are used for these events.
@defproc[(key-event? [x any]) boolean?]{
determines whether @racket[x] is a @tech{KeyEvent}}