Would let* mostly achieve this?
(define (get-x-spot char-width)
(let* ([dc (and char-width (get-dc))]
[style (and dc (or (send (get-style-list) find-named-style
"Standard")
(send (get-style-list) find-named-style
"Basic")))]
[fnt (and style (send style get-font))])
(when fnt
(define-values (xw _1 _2 _3) (send dc get-text-extent "x" fnt))
(+ left-padding (* xw char-width)))))
On Tue, Jun 11, 2013 at 12:49 PM, Laurent <laurent.ors...@gmail.com> wrote:
> 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
>
>
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