On Sun, 22 Jun 2014 11:25:01 -0400
Matthias Felleisen <matth...@ccs.neu.edu>
wrote:
>
> I would use Real for the parameter type and then cast twice:
>
> (define parms
> (command-line
> #:program "mypgm"
> #:once-each
> [("-v" "--verbose") "Show verbose output" (opt-verbose-mode #t)]
> [("-m" "--max-size")
> NUM
> ("Max size." "NUM")
> (opt-max-size (cast (string->number (cast NUM String)) Real))]))
>
> The casts bring out that you are willing to sacrifice precision of
> error messages for concision in code.
>
Thanks for this. I like this more than the guard solution although when
typing a non number for instance the error messages are a bit wild for
an ordinary user. Perhaps then I have to write my own string->number in
order to give a good error message if the parameter is a non number.
--
Manfred
>
>
>
>
> On Jun 22, 2014, at 12:06 AM, Manfred Lotz wrote:
>
> > On Sat, 21 Jun 2014 10:12:27 -0400
> > "Alexander D. Knauth"
> > <alexan...@knauth.org> wrote:
> >
> >> The first thing I notice is that opt-max-size is a (Parameterof
> >> Any), but you use string->number on it. So you should probably put
> >> a guard on the opt-max-size parameter something like this: (:
> >> opt-max-size (Parameterof Any Real)) (: opt-max-size-guard (Any ->
> >> Real)) (define (opt-max-size-guard val)
> >> (cond [(real? val) val]
> >> [(string? val) (opt-max-size-guard (string->number val))]
> >> [else (error "Max size: must be a real number")]))
> >>
> >> (define opt-max-size (make-parameter 0 opt-max-size-guard))
> >>
> >
> > Thanks for this, which works fine. I'm not qite sure I like this as
> > it seems to make the code more complicated. But if this is the only
> > possibility what can be done.
> >
> >
> >
> >> On Jun 21, 2014, at 3:45 AM, Manfred Lotz
> >> <manfred.l...@arcor.de> wrote:
> >>
> >>> Hi there,
> >>> I try to change one of my programs to typed racket and fail
> >>> because of errors when dealing with command line arguments.
> >>>
> >>> Here a minimum example:
> >>>
> >>> #lang typed/racket/base
> >>>
> >>> (require racket/cmdline)
> >>>
> >>>
> >>> (: opt-verbose-mode (Parameterof Boolean))
> >>> (define opt-verbose-mode (make-parameter #f))
> >>> (: opt-max-size (Parameterof Any))
> >>> (define opt-max-size (make-parameter "0"))
> >>>
> >>>
> >>>
> >>> (define parms
> >>> (command-line
> >>> #:program "mypgm"
> >>> #:once-each
> >>> [("-v" "--verbose") "Show verbose output" (opt-verbose-mode #t)]
> >>> [("-m" "--max-size") NUM ("Max size." "NUM") (opt-max-size NUM) ]
> >>> ))
> >>>
> >>>
> >>> (define (myfun)
> >>> (when (opt-verbose-mode)
> >>> (if (> (string->number (opt-max-size)) 0)
> >>> #t
> >>> #f)))
> >>>
> >>>
> >>> What do I do wrong? Any hint appreciated.
> >>>
> >>> --
> >>> Thanks,
> >>> Manfred
> >>>
> >>>
> >>>
____________________
Racket Users list:
http://lists.racket-lang.org/users
