[Haskell-beginners] confused by <-
David McBride
toad3k at gmail.com
Thu Sep 27 19:45:38 CEST 2012
Ignore my message. I think I'm looking at the wrong version of simpleHttp
or something. I should have tried it in ghci before I posted.
On Thu, Sep 27, 2012 at 1:43 PM, David McBride <toad3k at gmail.com> wrote:
> I think what he is asking is if try (from lifted) has type
>
> try :: (MonadBaseControl<http://hackage.haskell.org/packages/archive/monad-control/0.3.1.4/doc/html/Control-Monad-Trans-Control.html#t:MonadBaseControl>
> IO<http://hackage.haskell.org/packages/archive/base/4.5.0.0/doc/html/System-IO.html#t:IO>m,
> Exception<http://hackage.haskell.org/packages/archive/base/4.5.0.0/doc/html/Control-Exception-Base.html#t:Exception>e) => m a -> m (
> Either<http://hackage.haskell.org/packages/archive/base/4.5.0.0/doc/html/Data-Either.html#t:Either>e a)
>
> and simpleHttp is
>
> simpleHttp "googe" :: IO<http://hackage.haskell.org/packages/archive/base/4.6.0.0/doc/html/System-IO.html#t:IO>(
> Result<http://hackage.haskell.org/packages/archive/HTTP/latest/doc/html/Network-Stream.html#t:Result>(
> Response<http://hackage.haskell.org/packages/archive/HTTP/latest/doc/html/Network-HTTP-Base.html#t:Response>ty))
>
> then how can the whole statement have
>
> try $ simpleHttp "goog" :: GHandler master sub (Either SomeException
> ByteString)
>
> when the m in both parts of try is the same, it should end up IO not
> GHandler master sub. So I don't understand why this would work, either.
>
>
> On Thu, Sep 27, 2012 at 1:33 PM, Brent Yorgey <byorgey at seas.upenn.edu>wrote:
>
>> On Thu, Sep 27, 2012 at 10:01:25AM -0700, Bryce Verdier wrote:
>> > On 9/26/12 6:00 PM, Ertugrul Söylemez wrote:
>> > >Bryce Verdier <bryceverdier at gmail.com> wrote:
>> > >
>> > >> body <- L.try (simpleHttp "http://www.google.com") :: IO
>> (Either
>> > >>L.SomeException Data.ByteString.Lazy.Internal.ByteString)
>> > >Almost right, but your type signature is lying. =)
>> > >
>> > >
>> > >Greets,
>> > >Ertugrul
>> >
>> > Thanks for your hint, with a fair amount of head bashing against a
>> > wall I was able to figure this out. At the end of day I got :
>> >
>> > body <- try (simpleHttp "http://www.google.com") :: GHandler
>> > PlayHaven PlayHaven (Either SomeException ByteString)
>>
>> Do you need a type signature there at all?
>>
>> -Brent
>>
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>
>
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