[racket] display problem

Op 6-4-2012 9:20, Danny Yoo schreef:
>
>
> On Friday, April 6, 2012, Roelof Wobben wrote:
>
>     Op 5-4-2012 20:29, Danny Yoo schreef:
>
>             I start with this :
>
>             aaaaa|
>
>
>         Concretely, what does the editor world value look like at this
>         point?
>         You're representing the state somewhat ambiguously.  Can you
>         represent
>         the above in terms of (make-editor ... ...)?
>
>
>
>     Yes, (make-editor  aaaaaa    a  """)
>
>
> This can't be, as make-editor can only take two strings.  The 
> structure definition of make editor is:
>
>     (define-struct editor (pre post))
>
> Where both pre and post are both strings.
>
>             now someone press 3 times the left key.
>             So I have  aa/aaa
>
>
>     rep has he value of aaaaa
>     s has the value of a
>     t has also the value of a.
>
>
>
> You make the same conceptual mistake here.  This representation does 
> not fit the shape of the structure definition.
>
>
> Go back and make sure you understand the data definition.  If you have 
> questions about it, please feel free to ask.


Oke,
Back to the beginning.

In the text is noted.
(define-struct 
<http://docs.racket-lang.org/htdp-langs/beginner.html#%28form._%28%28lib._lang%2Fhtdp-beginner..rkt%29._define-struct%29%29>editor(prepost)) 

;Editor= (make-editorStringString)
;interp. (make-editorst)means the text in the editor is
;(string-append 
<http://docs.racket-lang.org/htdp-langs/beginner.html#%28def._%28lib._htdp-beginner..rkt._lang%29._%28%28lib._lang%2Fhtdp-beginner..rkt%29._string-append%29%29>st)with 
the cursor displayed between sand t



So for aaaaaaa| s has the value of aaaaa en t has the value of ""
For aaaa|aaaa s  I think s has the value of aaaaa and t has the value of aaa

I have a idea.
If I use the length of the first string and I press one time on the 
left-key then the new-length could be the old-one - 1. Then I could use 
substring to cut that part away.
The t part I could say if it's empty substring ( s , (string-lenght s), 
1) and if it's not empty use a string-append.

Am I on the right track ?

Roelof

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.racket-lang.org/users/archive/attachments/20120406/ebf52e77/attachment.html>