Awesome. Thanks! Where can I find the documentation for this TR reader syntax?

Why is TR not able to figure out the type for these variables without human 
help? Does that mean the implementation of `command-line` is in TR and the 
types of those variables are inferred by the type system, or they are 
explicitly typed to be `Any` for simplicity? 


On Monday, March 6, 2017 at 2:48:15 PM UTC-8, Sam Tobin-Hochstadt wrote:
> You can use the #{x : T} reader syntax to annotate variables in macros
> like `command-line`. Here's a working version of your code:
> 
> ```
> #lang typed/racket
> 
> (define *channel* (make-parameter "#general"))
> (define *message* : (Parameterof (Listof String)) (make-parameter '()))
> 
> 
> (define (parse-cmdline)
>   (command-line
>    #:program "q"
>    #:once-each
>    [("-c" "--channel") #{ch : String} "slack channel to post (default:
> use .qrc setting or default)" (*channel* ch)]
>    #:args #{msg : String}
>    (*message* msg)))
> ```
> 
> On Mon, Mar 6, 2017 at 2:08 AM, kay <> wrote:
> > For a complex syntax form like `command-line`, I have difficulty correctly 
> > annotate the bindings it defines.
> >
> > More specifically, in the below code, for variable `msg`, even the 
> > document[1] says the `#:args` binds as list of **strings**, but the error 
> > indicates that it somehow is declared as `Listof Any`.
> >
> > Similarly, for variable `ch` bound in line 11, I believe it should always 
> > be `String`, but it somehow is declared to be `Any`.
> >
> > What should I do with this type of error, if I want my varaibles to be more 
> > precisely typed than just `Any`?
> >
> >
> > [1]: 
> > https://docs.racket-lang.org/reference/Command-Line_Parsing.html?q=command-line#%28form._%28%28lib._racket%2Fcmdline..rkt%29._command-line%29%29
> >
> > ```
> >  1      #lang typed/racket
> >  2
> >  3      (define *channel* (make-parameter "#general"))
> >  4      (define *message* : (Parameterof (Listof String)) (make-parameter 
> > '()))
> >  5
> >  6
> >  7      (define (parse-cmdline)
> >  8          (command-line
> >  9           #:program "q"
> > 10           #:once-each
> > 11           [("-c" "--channel") ch "slack channel to post (default: use 
> > .qrc setting or default)" (*channel* ch)]
> > 12           #:args msg
> > 13           (*message* msg)))
> > 14
> > 15
> > 16      #|
> > 17      tr.rkt:11:91: Type Checker: Wrong argument to parameter - expected 
> > String and got Any in: (*channel* ch)
> > 18      tr.rkt:13:5: Type Checker: Wrong argument to parameter - expected 
> > (Listof String) and got (Listof Any) in: (*message* msg)
> > 19      |#
> > ```
> >
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