From daniel.trstenjak at gmail.com  Wed Jul  1 08:31:35 2020
From: daniel.trstenjak at gmail.com (Daniel Trstenjak)
Date: Wed, 1 Jul 2020 10:31:35 +0200
Subject: [Haskell-beginners] How to structure an application?
In-Reply-To: <e61f28b3-2f08-38a8-ede1-7ae7d064ea53@gmx.de>
References: <e61f28b3-2f08-38a8-ede1-7ae7d064ea53@gmx.de>
Message-ID: <20200701083135.GB3366@octa>

Hi Tilmann,

> wxApp :: (MonadReader Handle m, MonadIO m) => m ()
> wxApp = do
>   ping -- this works, but I don't need it here..
>   liftIO $ do
>     f <- frame [ ]
>     timer f [ interval := 1000
>             -- , on command := hputStrLn h "ping" -- this is what I try
> to avoid
>             -- , on command := ping -- of course, this doesn't work, but
> it would be so nice..
>             , enabled := True]
>     return ()

I assume that WX expects an 'IO' action for the 'command', but 'ping' is
an action of the 'ReaderT' monad.

WX won't be able to execute this action, because it doesn't know
anything about the 'ReaderT' monad, so there's no 'Handle' that
it could give to the 'ping' function.

I think the most straight forward solution is to have a function 'ping':

   ping :: Handle -> IO ()
   ping h = hputStrLn h "ping"


And then a 'wxApp' like:
      
   wxApp :: (MonadReader Handle m, MonadIO m) => m ()
   wxApp = do
     handle <- ask
     liftIO $ do
       f <- frame [ ]
       timer f [ interval := 1000, on command := ping handle, enabled := True]
       return ()


So instead of having 'ping' in the 'ReaderT' monad you just give it
explicitly the data of the monad.


You could have a helper function that does this transformation:

   handlize :: (MonadReader Handle m, MonadIO m) => (Handle -> IO()) -> m (IO ())
   handlize func = do
     handle <- ask
     return $ func handle

   wxApp :: (MonadReader Handle m, MonadIO m) => m ()
   wxApp = do
     cmd <- handlize ping
     liftIO $ do
       f <- frame [ ]
       timer f [ interval := 1000, on command := cmd, enabled := True]
       return ()


Greetings,
Daniel

From sudaraka at sudaraka.org  Tue Jul 28 08:11:33 2020
From: sudaraka at sudaraka.org (Sudaraka Wijesinghe)
Date: Tue, 28 Jul 2020 13:41:33 +0530
Subject: [Haskell-beginners] Need help setting up development environment
	via ghcup
Message-ID: <20200728081142.DE586328005D@mailuser.nyi.internal>

Hi,

I have successfully installed `ghc` (8.8.4), `cabal-install` (3.2.0.0) via
`ghcup` (0.1.8) and created/build and several example projects without any
issues. In one of the projects I want to create a binary distribution
tarball. For this I tried using `runhaskell Setup.hs copy` (configure before
that) at one of the steps, and got the following error.

```
Configuring my-project-0.1.0.0...
Setup.hs: Encountered missing or private dependencies:
optparse-applicative ==0.15.*
```

`optparse-applicative` is a dependency of my project and it was installed by
`cabal build`.

I figured out this is because `cabal-install` and `runhaskell` (or `ghc` or
`ghc-pkg`) used different package DBs.

- `cabal-install` -> ~/.cabal/store/ghc-8.8.4/
- `runhaskell` -> ~/.ghcup/ghc/8.8.4/lib/ghc-8.8.4/

Is there a was I can make both `cabal-install` and `runhaskell` use the same
package DB (or use both of them)?

[X-POST:
https://www.reddit.com/r/haskellquestions/comments/hydge5/need_help_setting_up_development_environment_via/] 
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 833 bytes
Desc: OpenPGP digital signature
URL: <http://mail.haskell.org/pipermail/beginners/attachments/20200728/06b575ba/attachment.sig>