Conceptually you want to signal the error out of the 'parms' computation. So even if you introduce string->real as a variation on string->number, you probably want to catch the error it raises and re-cast it as 'params' message.
On Jun 22, 2014, at 12:56 PM, Manfred Lotz wrote: > On Sun, 22 Jun 2014 11:58:59 -0400 > Sam Tobin-Hochstadt <sa...@cs.indiana.edu> > wrote: > >> 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 >> > > This is indeed nice. Thanks for the variation to Matthias solution. > > -- > Manfred > >> >> On Sun, Jun 22, 2014 at 11:25 AM, 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. >>> >>> -- Matthias >>> >>> >>> >>> >>> 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 ____________________ Racket Users list: http://lists.racket-lang.org/users
