Op 19-4-2012 22:08, namekuseijin schreef:
On Thu, Apr 19, 2012 at 11:04 AM, Roelof Wobben <r.wob...@home.nl
<mailto:r.wob...@home.nl>> wrote:
> (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))]
> [ (and (key=? "\b" k) (equal? (string-length (editor-pre e))
0)) e]
> [ ( or (key=? "\t" k) (key=? "\u007F" k)) e]
> [ ( > (string-length k) 1) e ]
> [else (make-editor (string-append (editor-pre e) k) (editor-post
e))]
> ))
I'd rewrite that as:
(define (edit e k)
(let ([pre (editor-pre e)]
[post (editor-post e)]
[size string-length]
[s+ string-append])
(cond
[(and (key=? "right" k) (> (size post) 0)) (make-editor (s+ pre
(string-first post)) (string-rest post))]
[(and (key=? "left" k) (> (size pre) 0)) (make-editor
(string-remove-last pre) (s+ (string-last pre) post))]
[(and (key=? "\b" k) (> (size pre) 0)) (make-editor
(string-remove-last pre) post)]
[(and (key=? "\b" k) (= (size pre) 0)) e]
[(or (key=? "\t" k) (key=? "\u007F" k)) e]
[(> (size k) 1) e]
[else (make-editor (s+ pre
k) post)])))
Thanks,
I see how it works but the htdp2e book let is in a later chapter then I
study now.
Roelof
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