When I see what Robby is forced to write when following the Style:
https://github.com/plt/racket/commit/09d636c54573522449a6591c805b38f72b6f7da8#L4R963
I cannot help but think that something is wrong somewhere (it may not be
the Style, and in case it wasn't clear I'm certainly not criticizing
Robby's code).
Using `let' and `and' instead, although being a bit better since it avoids
all the [else #f], is not that big an improvement:
(define (get-x-spot char-width)
(and
char-width
(let ([dc (get-dc)])
(and
dc
(let ([style (or (send (get-style-list) find-named-style "Standard")
(send (get-style-list) find-named-style "Basic"))])
(and
style
(let*-values ([(fnt) (send style get-font)]
[(xw _1 _2 _3) (send dc get-text-extent "x" fnt)])
(+ left-padding (* xw char-width)))))))))
Actually I think here the right thing to do might be to allow for internal
definitions inside `and':
(define (get-x-spot char-width)
(and char-width
(define dc (get-dc))
dc
(define style (or (send (get-style-list) find-named-style "Standard")
(send (get-style-list) find-named-style "Basic")))
style
(define fnt (send style get-font))
(define-values (xw _1 _2 _3) (send dc get-text-extent "x" fnt))
(+ left-padding (* xw char-width))))
Isn't it *much* more readable? (shorter, avoid rightward drift, less
parens, vertical alignment)
Since it's not the first time I find the need for such internal definitions
in `and', maybe this is something to consider for future addition to
Racket? Or have some people already identified some problems with this idea?
I've played a bit with it if you want to try by your own:
https://gist.github.com/Metaxal/5758394
(not sure I got it all good with syntax-parse though)
Laurent
____________________
Racket Users list:
http://lists.racket-lang.org/users
