[racket] Question about match in typed/racket

Unfortunately, this seems not to work with Typed Racket.  I'm not
quite sure why -- something is going wrong in how it tries to figure
out the types of the internal variables generated by the expansion of
`match'.  I will look into this further, thanks for letting me know.

On Fri, Apr 13, 2012 at 9:43 PM, Timothy Nelson <tbnelson at gmail.com> wrote:
> One more question. Thanks for your patience. :-)
>
> I had this before:
> (list args ...)
>
> which became:
> (list #{args : (Listof Sexp)} ...)
>
> Now suppose I want to match only a list of *symbols* instead of a list of
> Sexps, finishing with a symbol bound separately. In normal Racket, this
> would be:
>
>> (match '(a b c)
>     [(list (? symbol? args) ... (? symbol? lastarg))
>      (list args lastarg)])
> '((a b) c)
>
> If I leave this as-is in typed/racket I naturally get the same error as
> before, but if I annotate args in the same way as in my last question:
> (list (? symbol? #{args : (Listof Symbol)}) ... (? symbol? lastarg))
>
> I get a bizarre type error: "Type Checker: Expected (Listof Symbol), but got
> (Listof Any) in:", and then my entire (match ...).
>
> If I annotate the (? symbol args) instead of just args -- I wasn't sure what
> the right syntax was -- I get the original expected (Listof Symbol) got
> (Listof Any) error.
>
> Am I mis-using annotations?
>
> Thanks,
> - Tim
>
>
> On Thu, Apr 12, 2012 at 12:48 PM, Timothy Nelson <tbnelson at gmail.com> wrote:
>>
>> That fixes it for me. Thanks, both of you!
>>
>>
>> On Thu, Apr 12, 2012 at 12:27 AM, Sam Tobin-Hochstadt <samth at ccs.neu.edu>
>> wrote:
>>>
>>> On Wed, Apr 11, 2012 at 3:36 PM, Timothy Nelson <tbnelson at gmail.com>
>>> wrote:
>>> >
>>> > I'd like to write a function that consumes an s-expression and produces
>>> > a
>>> > struct -- something similar to building a tree struct out of a tree
>>> > sexp. In
>>> > the past, I've always used match for this kind of sexp manipulation.
>>> > However, if I have a match clause within a function like this:
>>> >
>>> > (: my-func (Sexp -> mystruct))
>>> > (define (my-func s)
>>> >   (match s
>>> >     [(list args ...) (make-mystruct (map my-func args))]))
>>>
>>> The problem here is that Typed Racket can't guess what type you mean
>>> for `args' to have, so you have to tell it when you bind `args'.  That
>>> looks like this:
>>>
>>> (: my-func (Sexp -> mystruct))
>>> (define (my-func s)
>>>  (match s
>>>    [(list #{args : (Listof Sexp)} ...)
>>>     (make-mystruct (map my-func args))]))
>>>
>>> which typechecks correctly for me.
>>> --
>>> sam th
>>> samth at ccs.neu.edu
>>
>>
>
>
> ____________________
>  Racket Users list:
>  http://lists.racket-lang.org/users
>



-- 
sam th
samth at ccs.neu.edu