[racket] Style or and/define

Okay, there is one difference between our examples, in that yours will
short-circuit and mine won't. However, if that is not a concern and you're
looking more for readability, you could even use local define

(define (get-x-spot char-width)
  (define dc (and char-width (get-dc)))
  (define style (and dc (or (send (get-style-list) find-named-style
"Standard")
                            (send (get-style-list) find-named-style
"Basic"))))
  (define 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 1:04 PM, Sean McBeth <sean.mcbeth at gmail.com> wrote:

> 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
>>
>>
>> ____________________
>>   Racket Users list:
>>   http://lists.racket-lang.org/users
>>
>>
>
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