You may use srfi/2 http://docs.racket-lang.org/srfi-std/srfi-2.html
(require srfi/2) (define (get-x-spot char-width) (and-let* ([char-width] [dc (get-dc)] [style (or (send (get-style-list) find-named-style "Standard") (send (get-style-list) find-named-style "Basic"))]) (let*-values ( [(fnt) (send style get-font)] [(xw _1 _2 _3) (send dc get-text-extent "x" fnt)]) (+ left-padding (* xw char-width)))))) Вторник, 11 июня 2013, 18:49 +02:00 от Laurent <laurent.ors...@gmail.com>: >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 > -- Роман Клочков
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