Ah, very good, that's much better. Mystery solved. (though I do kind of like the `and-let' with `#:let' keywords, since it avoids the paren-verbosity of `let'.)
Thanks Клочков and Matthias, Laurent On Tue, Jun 11, 2013 at 8:44 PM, Matthias Felleisen <matth...@ccs.neu.edu>wrote: > > Nice, I wish Oleg had also defined let*-and, which is what I think you > really want here: > > (define-syntax let*-and > (syntax-rules () > [(_ ((x:id e:expr) (y:id f:expr) ...) body0:def-or-expr body1 ...) > (let ((x:id e:expr)) > (and x:id (let*-and ((y:id f:expr) ...) body0:def-or-expr body1 > ...)))] > [(_ ((x:id) (y:id f:expr) ...) body0:def-or-expr body1 ...) > (let ((x:id x:id)) > (and x:id (let*-and ((y:id f:expr) ...) body0:def-or-expr body1 > ...)))] > [(_ () body0:def-or-expr body1 ...) > (let () > body0:def-or-expr > body1 ...)])) > > ;; ---------------------------------------------------------------- > > (class object% > (super-new) > > (define/private (get-x-spot.v2 char-width) > (let*-and ([char-width] > [dc (get-dc)] > [style (or (send (get-style-list) find-named-style > "Standard") > (send (get-style-list) find-named-style > "Basic"))]) > (define-values (fnt) (send style get-font)) > (define-values (xw _1 _2 _3) (send dc get-text-extent "x" fnt)) > (+ left-padding (* xw char-width))))) > > -- Matthias > > > > > On Jun 11, 2013, at 1:39 PM, Клочков Роман wrote: > > You may use srfi/2 http://docs.racket-lang.org/srfi-std/srfi-2.html > > (require srfi/2) > (define (get-x-spot char-width) > (and-let* > ([char-width] > [dc (get-dc)] > [style (or (send (get-style-list) find-named-style "Standard") > (send (get-style-list) find-named-style "Basic"))]) > (let*-values ([(fnt) (send style get-font)] > [(xw _1 _2 _3) (send dc get-text-extent "x" fnt)]) > (+ left-padding (* xw char-width)))))) > > > Вторник, 11 июня 2013, 18:49 +02:00 от Laurent <laurent.ors...@gmail.com>: > > 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 > > > > -- > Роман Клочков > ____________________ > Racket Users list: > http://lists.racket-lang.org/users > > >
____________________ Racket Users list: http://lists.racket-lang.org/users
