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