Hello,
I'm trying to figure out how I would make a text editor or a DrRacket extension
that circled nested s-expressions instead of displaying the parentheses.
DrRacket circles text for the find/replace feature, so I looked at that and
found that it uses the highlight-range method of text:basic<%> in framework.
However, when I tried using it with the #:adjust-on-insert/delete argument as
#true, I got strange behavior with my little toy editor.
When I start typing something like "(define (f x)", it circles the (f x) like I
expected. However, when I continue typing, that's when I get the weird
behavior. For example, if I type a return, the beginning of the circle jumps
backwards to the "(define", and the end of the circle jumps down with the
cursor. Then if I press delete after more typing, that circle disappears and is
replaced by a narrow ellipse that just follows my cursor around. This weird
behavior goes away when the #:adjust-on-insert/delete argument is #false.
Is there a way to stay on the positions of the open and close parentheses
without jumping backwards or collapsing and following the cursor? To do that,
it needs to shift positions when I insert or delete characters, but is there a
way to tell it to stay where it is if I insert something right after the close
parenthesis?
#lang racket/base
(require racket/class racket/gui/base framework)
(define frame
(new frame% [label "circledit"] [width 500] [height 500]))
(define text-editor
(new (class racket:text%
(super-new)
(inherit get-start-position get-backward-seep)
;; when an s-expr is closed, this method will be called
(define/override (balance-parens key-event)
(super balance-parens key-event)
;; and it will circle the s-expr that was just closed
(define end
(get-start-position))
(define start
(get-backward-sexp end))
(when start
(send text-editor highlight-range
start end "dark green" #f 'low 'hollow-ellipse
#:adjust-on-insert/delete? #t))))))
(define canvas
(new editor-canvas% [parent frame] [editor text-editor]))
(send frame show #true)
Alex Knauth
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