>
> > (define default (gensym))
> > (define (default? x) (equal? x default))
>
> (Using `eq?' here is a common idiom.)
>
ah, of course, thanks for the reminder.
>
> In any case, the real point here is not the macro -- it's the
> existence of a special `none' value that marks an unsupplied value.
On Tue, Feb 14, 2012 at 17:45, Chongkai Zhu wrote:
> I simply use
>
> (define (bar . x)
> (apply foo 5 x))
>
Yes, but that does not work if the specified optional argument is not the
first one (and not the last one).
That works if all default arguments are all keyword-based though (using
keywor
On 2/11/2012 10:55 AM, Laurent wrote:
Hi,
Often I'd like to make a wrapper for a given function that has default
values (possibly with keywords).
So if I want my function to have the same default values for one
particular optional argument, I need to redefine it myself.
For example, suppose
On 2/11/2012 10:55 AM, Laurent wrote:
Hi,
Often I'd like to make a wrapper for a given function that has default
values (possibly with keywords).
So if I want my function to have the same default values for one
particular optional argument, I need to redefine it myself.
For example, suppose
9 hours ago, Laurent wrote:
> Thank you all for your good and helpful answers. Based on them,
> here is my current solution (without keywords), using macros to ease
> the function definition:
>
> #lang racket
>
> (define default (gensym))
> (define (default? x) (equal? x default))
(Using `eq?'
Thank you all for your good and helpful answers.
Based on them, here is my current solution (without keywords), using macros
to ease the function definition:
#lang racket
(define default (gensym))
(define (default? x) (equal? x default))
(define-syntax parse-args-body
(syntax-rules ()
; w
Four hours ago, Laurent wrote:
>
> (define (foo arg1 [arg2 ])
> )
>
> (define (bar [arg2 ])
> (foo 5 arg2))
Robby's suggestion is basically:
(define (foo x [y #f])
(let ([y (or y )])
...))
(define (bar [y #f])
(foo 5 y))
If #f is a valid value, the common way to deal
Would this help you, suitable wrapped up as a macro:
#lang racket
(struct f (g default) #:property prop:procedure (struct-field-index g))
(define f* (f (lambda (x [y ((f-default f*))]) (+ x y)) (lambda () 99)))
(define (f-wrapper f-ish)
(lambda (g [d ((f-default f-ish))]) ;; all you need
On Sat, Feb 11, 2012 at 15:07, Rodolfo Carvalho wrote:
> Hello,
>
> On Sat, Feb 11, 2012 at 14:55, Laurent wrote:
>
>> ...
>>
>> (define (bar [arg2 (get-default-value foo arg2)])
>> (foo 5 arg2))
>>
>>
>>
> Maybe someone will have a better idea (or a brighter implementation), but
> if not, here
Hello,
On Sat, Feb 11, 2012 at 14:55, Laurent wrote:
> ...
>
> (define (bar [arg2 (get-default-value foo arg2)])
> (foo 5 arg2))
>
>
>
Maybe someone will have a better idea (or a brighter implementation), but
if not, here's my contribution:
#lang racket
(require rackunit)
(define (foo arg1 [
FWIW, reasons like this is why most of the standard libraries have #f or
some other simple value for a default. Then, the "real" default is computed
in the body.
Robby
On Saturday, February 11, 2012, Laurent wrote:
> Hi,
> Often I'd like to make a wrapper for a given function that has default
va
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