[racket] key event problem

Op 18-4-2012 12:32, Pierpaolo Bernardi schreef:
> On Wed, Apr 18, 2012 at 11:17, Roelof Wobben<r.wobben at home.nl>  wrote:
>> Hello,
>>
>> I try to make a function which controls the key-events.
>>
>> The function does only have to react on backspace , left , right .
>> Give no reaction on tab , rubout or the other keys with a length more then
>> 1.
>> When given another key with length 1 it has to insert the key.
>>
>> So i thought this would work :
>>
>> (define (edit e k)
>>   (cond
>>      [  (and(key=? "right" k) (>  (string-length (editor-post e)) 0))
>> (make-editor(string-append (editor-pre e) (string-first (editor-post e) ))
>> (string-rest (editor-post e) ))]
>>      [  (and(key=? "left" k) (>  (string-length (editor-pre e)) 0))
>> (make-editor ( string-remove-last (editor-pre e) ) (string-append
>> (string-last(editor-pre e))  (editor-post e)))]
>>      [  (and (key=? "\b" k) (>  (string-length (editor-pre e)) 0))
>> (make-editor (string-remove-last (editor-pre e)) (editor-post e))]
>>      [  (not ( or (key=? "\t" k ) (key=? "\u007F" k) (key=? "right" k))) (
>> string-append (editor-pre e) k)]
>>      [else e]
>>      ))
>>
>> but now when someone press the right-key the first get executed but also the
>> not rule.
>> I thought that cond works if one rule is true the other gets ignored. But it
>> looks like that's not true.
>>
>> Now my question is : how can I take care that all the other key's with
>> length 1 except backspace, tab, and rubout get's executed ?
> maybe:
>
> (define (edit e k)
>    (cond ((key=? "right" k)
>           (if (zero? (string-length (editor-post e)))
>             e
>             <create an updated new editor>))
>          ((key=? "left" k)
>           (if (zero? (string-length (editor-pre e)))
>             e
>             <create an updated new editor>))
>          ...
>          ))
>
> ?
>

oke, but why string-length 0 . In my opinion the string-length of the 
key is 1 or more then 1.

So I thought of this :

(define (edit e k)
  (cond
     [  (and(key=? "right" k) (>  (string-length (editor-post e)) 0))
(make-editor(string-append (editor-pre e) (string-first (editor-post e) ))
(string-rest (editor-post e) ))]
     [  (and(key=? "left" k) (>  (string-length (editor-pre e)) 0))
(make-editor ( string-remove-last (editor-pre e) ) (string-append
(string-last(editor-pre e))  (editor-post e)))]
     [ (and (>(string-length k)1) (not (or(key=? "left" k) (key=? "right" k))) e
     [  (and (key=? "\b" k) (>  (string-length (editor-pre e)) 0))
(make-editor (string-remove-last (editor-pre e)) (editor-post e))]
     [  (and (equal (string-length k)1) (not ( or (key=? "\t" k ) (key=? "\u007F" k) (key=? "bs" k))) (
string-append (editor-pre e) k)]
     [else e]
     ))

This is not tested and can have bugs.

Roelof