Ah I found documentation for `#{ x : ... }` at here[1].
[1]:
https://docs.racket-lang.org/ts-guide/more.html#%28part._.Annotating_.Single_.Variables%29
On Monday, March 6, 2017 at 9:50:39 PM UTC-8, lu wrote:
> 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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