[racket] Style or and/define

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.orseau at 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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