[Haskell-beginners] Get responsecode(Int) from simpleHTTP's Response

[Jacques du Rand]

Michael
That's a fantastic explanation !
I appreciate the time taken  and depth of it !

Best Regards
Jacques




On Wed, Oct 17, 2012 at 1:52 PM, Michael Orlitzky <michael at orlitzky.com>wrote:

> On 10/17/2012 02:51 AM, Jacques du Rand wrote:
> > This is great works perfectly !
> > I'm so new at haskell its scary !
> >
> > One last question i dont *understand* one line ( just the right side )
> >
> >        let (x,y,z) = rspCode response
> >
> > 1) If i look at the documentation: Sorry for HTML. I see the
> > constructors of Response and below it rspCode,rspReason,rspHeaders etc
> > Are those parters or functions ?
>
> They're functions that you can think of as the names of attributes of a
> Response object (if you're coming from object-oriented programming).
> There's a little magic going on under the hood, so you might want to
> check out e.g.,
>
>   http://learnyouahaskell.com/making-our-own-types-and-typeclasses
>
> In particular the "Record Syntax" section. Papering over the details, in
> an OO language, you might do something like,
>
>   response.rspCode
>
> to get the code out of a Response object. In Haskell, we just use a
> function to do it. So,
>
>   rspCode response
>
> calls the rspCode function on 'response'. If you check the API docs,
>   >
>
> http://hackage.haskell.org/packages/archive/HTTP/4000.0.7/doc/html/Network-HTTP-Base.html#t:Response
>
> you should see that rspCode takes a Response object and returns a
> ResponseCode. But ResponseCode is just a synonym for (Int,Int,Int):
>
>   type ResponseCode = (Int, Int, Int)
>
> Therefore, rspCode takes a Response, and gives you back three Ints in an
> ordered triplet.
>
>
> > 2) I see the new version has a getResponseCode functions like
> > getResponseBody with the signature:
> > getResponseCode :: Result (Response a) -> IO ResponseCode
> > getResponseCode (Left err) = fail (show err)
> > getResponseCode (Right r)  = return (rspCode r)
> >
> > What does this mean in the signature  *Result (Response a)*
>
> The Result type is really just a wrapper around Either. Either usually
> takes two parameters, but Result fixes one of them to be ConnError:
>
>   type Result a = Either ConnError a
>
> So Result still takes one parameter. The parameter in this case is
> (Response a).
>
> For a more concrete example, think of a data type where you've got a box
> and you can put stuff in it.
>
>   data Box a = Box a
>
> The 'a' parameter means that we can put different types of stuff in the
> box. For example,
>
>   foo :: Box Int
>   foo = Box 3
>
>   bar :: Box String
>   bar = Box "Hello"
>
> If this makes sense to you, then (Result (Response a)) is doing exactly
> the same thing as (Box Int) or (Box String), only with slightly more
> complicated types.
>
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