Great question! Many libraries use a monad transformer stack on top of IO rather than a direct IO interface. This can be convenient if you are also using such a stack, but it certainly complicates things a bit if you're just in IO directly.

If you follow the error messages it says that it's expecting your Monad to have an instance of MonadResource. IO does not (or else it would've just worked). This means that you'll need to find a monad transformer that provides MonadResource. By looking at the name "Control.Monad.Trans.Resource.Internal.MonadResource" I know that I should probably start looking for something called "Control.Monad.Trans.Resource". After a bit of searching on Hackage I found http://hackage.haskell.org/package/resourcet

The relevant function is `runResourceT` (most monad transformers are going to have a similarly named run function to "unwrap" a transformer): http://hackage.haskell.org/package/resourcet-1.1.5/docs/Control-Monad-Trans-Resource.html#v:runResourceT

Something like this should compile:

{-# LANGUAGE OverloadedStrings #-}

import Network.HTTP.Client

import Instagram

import Control.Monad.Trans.Resource

code = "xxx_some_code"

redirectUrl = "http://localhost:9988/instagram/oauth2/callback"

credentials = Credentials "xxx_some_api_id" "xxx_some_api_secret"

main :: IO ()

main = do

manager <- newManager defaultManagerSettings

token <- runResourceT . runInstagramT credentials manager $

getUserAccessTokenURL2 redirectUrl code

print token

On Sat, Jul 11, 2015 at 5:16 AM, René Klačan <rene.klacan@gmail.com> wrote:

Hi all,

I've been trying to create working example with "ig" https://hackage.haskell.org/package/ig-0.2.2 - library over instagram API and I am facing little monad problem.

Can someone advise me please how to make this small piece of code work?

{-# LANGUAGE OverloadedStrings #-}

import Network.HTTP.Client
import Instagram

code = "xxx_some_code"
redirectUrl = "http://localhost:9988/instagram/oauth2/callback"
credentials = Credentials "xxx_some_api_id" "xxx_some_api_secret"

main :: IO ()
main = do
manager <- newManager defaultManagerSettings
token <- runInstagramT credentials manager $
getUserAccessTokenURL2 redirectUrl code
print token

I am getting following error:

src/Main.hs:14:9:
No instance for (Control.Monad.Trans.Resource.Internal.MonadResource
IO)
arising from a use of ‘getUserAccessTokenURL2’
In the second argument of ‘($)’, namely
‘getUserAccessTokenURL2 redirectUrl code’
In a stmt of a 'do' block:
token <- runInstagramT credentials manager
$ getUserAccessTokenURL2 redirectUrl code
In the expression:
do { manager <- newManager defaultManagerSettings;
token <- runInstagramT credentials manager
$ getUserAccessTokenURL2 redirectUrl code;
print token }

Thanks

Rene

_______________________________________________
Beginners mailing list
Beginners@haskell.org
http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners