[racket] Typed racket and command line parameters

Fortunately, one of those casts can be eliminated with a bit of type
annotation on `NUM`.   Full code here:
https://gist.github.com/samth/48bf2ccb2c510c75017e

(define parms
  (command-line
   #:program "mypgm"
   #:once-each
   [("-v" "--verbose") "Show verbose output" (opt-verbose-mode #t)]
   [("-m" "--max-size")
    #{NUM : String} ("Max size." "NUM")
    (opt-max-size (cast (string->number NUM) Real))]))

Sam


On Sun, Jun 22, 2014 at 11:25 AM, Matthias Felleisen
<matthias at 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.
>
> -- Matthias
>
>
>
>
> On Jun 22, 2014, at 12:06 AM, Manfred Lotz wrote:
>
>> On Sat, 21 Jun 2014 10:12:27 -0400
>> "Alexander D. Knauth"
>> <alexander at 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.lotz at 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
>>>>
>>>>
>>>>
>>>>
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