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
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-H...
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.