I've already extended and for my own purposes. Particularly, I sometimes want to use the result of an expression that's in the and without breaking out of the and, so I added a keyword #:bind id before any expression to bind id to the result for the remainder of the and. I would add defines to this extended and, but that requires a local-expand. Not sure if I want to do that. -Ian ----- Original Message ----- From: "Sean McBeth" <sean.mcb...@gmail.com> To: "Laurent" <laurent.ors...@gmail.com> Cc: "Racket Mailing List" <us...@lists.racket-lang.org> Sent: Tuesday, June 11, 2013 1:11:26 PM GMT -05:00 US/Canada Eastern Subject: Re: [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.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 ____________________ Racket Users list: http://lists.racket-lang.org/users
