On Tue, Jun 11, 2013 at 7:11 PM, Sean McBeth <sean.mcb...@gmail.com> wrote:
> 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))) > I do feel not short-circuiting is an issue, because then you have to read the whole code to understand that if char-width is false, all is false (and same for the others). Furthermore your `when' returns `(void)' and not `#f', so the code is not equivalent here, and I suspect you've written it this way exactly because you can't use `and' easily with the multiple values. Laurent > > 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 >>> >>> >> >
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