[Haskell-beginners] Beginners Digest, Vol 100, Issue 14
Lai Boon Hui
laiboonh at gmail.com
Sat Oct 22 13:47:28 UTC 2016
Hi David,
Thanks for chipping in. I found the solution to be to include "directory"
in cabal file "build-depends". I was confused because my stack ghci config
didn't need :m + System.directory to work. But somehow cabal repl does not
work without some kind of import.
On Sat, Oct 22, 2016 at 8:00 PM, <beginners-request at haskell.org> wrote:
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> Today's Topics:
>
> 1. cabal repl issue (Lai Boon Hui)
> 2. Re: cabal repl issue (David McBride)
> 3. Re: Monadic functions definitions for free monadic DSL
> (Sumit Raja)
> 4. Re: Monadic functions definitions for free monadic DSL
> (Kim-Ee Yeoh)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Fri, 21 Oct 2016 22:35:19 +0800
> From: Lai Boon Hui <laiboonh at gmail.com>
> To: beginners at haskell.org
> Subject: [Haskell-beginners] cabal repl issue
> Message-ID:
> <CAJdQggnSvw8z7V+SBY=y2TEfhpcK2znLHpkp9i+Edq5QAgXM7w at mail.
> gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Hi all,
>
> when i execute cabal repl i get this:
>
> <interactive>:1:8: error:
>
> Not in scope: ‘System.Directory.getCurrentDirectory’
>
> No module named ‘System.Directory’ is imported.
> because my ghci.conf has
> :def pwd (\_-> System.Directory.getCurrentDirectory >>= print >> return
> "")
>
> Does anyone know how i can include System.Directory somehow even though its
> not used in my cabal project?
>
> --
> Best Regards,
> Boon Hui
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> ------------------------------
>
> Message: 2
> Date: Fri, 21 Oct 2016 10:56:55 -0400
> From: David McBride <toad3k at gmail.com>
> To: The Haskell-Beginners Mailing List - Discussion of primarily
> beginner-level topics related to Haskell <beginners at haskell.org>
> Subject: Re: [Haskell-beginners] cabal repl issue
> Message-ID:
> <CAN+Tr42JiQ3x-MtrZXthx=PHjnJ+RH7zj3HJGQ6L+j7Y3cFcfw at mail.
> gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Just do this:
>
> :m +System.Directory
> :def pwd (\_ -> getCurrentDirectory >>= print >> return "")
>
> On Fri, Oct 21, 2016 at 10:35 AM, Lai Boon Hui <laiboonh at gmail.com> wrote:
>
> > Hi all,
> >
> > when i execute cabal repl i get this:
> >
> > <interactive>:1:8: error:
> >
> > Not in scope: ‘System.Directory.getCurrentDirectory’
> >
> > No module named ‘System.Directory’ is imported.
> > because my ghci.conf has
> > :def pwd (\_-> System.Directory.getCurrentDirectory >>= print >> return
> > "")
> >
> > Does anyone know how i can include System.Directory somehow even though
> > its not used in my cabal project?
> >
> > --
> > Best Regards,
> > Boon Hui
> >
> > _______________________________________________
> > Beginners mailing list
> > Beginners at haskell.org
> > http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
> >
> >
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> ------------------------------
>
> Message: 3
> Date: Sat, 22 Oct 2016 12:14:15 +1100
> From: Sumit Raja <sumitraja at gmail.com>
> To: beginners at haskell.org
> Subject: Re: [Haskell-beginners] Monadic functions definitions for
> free monadic DSL
> Message-ID:
> <CAD4nrSf68uPFaHKpHN01wJjhhMMO5tSBQqHfM1cBogphxvUihg at mail.
> gmail.com>
> Content-Type: text/plain; charset=UTF-8
>
> > I feel like if you can figure out what you actually want Accept to do, it
> > will become clearer. Here's my attempt. Accept takes a chan, takes a
> > procedure to loop on, a procedure to accept on, and then returns the
> server
> > chan to continue the loop. I don't know if this is entirely right, but
> it
> > type checks and hopefully it will give you some ideas.
>
> As you've said Accept needs refinement. I tried writing a interpretUDP
> which doesn't have an accept loop but does have a bind + listen. I
> suspect that accept needs to move into the interpretTCP somehow and
> the DSL needs to be Bind or similar. Bind makes more sense as well if
> I wanted to write a pipes or a chan based interpreter.
>
> Thanks for the rewrite and the pointers.
>
> -Sumit
>
>
> ------------------------------
>
> Message: 4
> Date: Sat, 22 Oct 2016 08:27:32 +0700
> From: Kim-Ee Yeoh <ky3 at atamo.com>
> To: The Haskell-Beginners Mailing List - Discussion of primarily
> beginner-level topics related to Haskell <beginners at haskell.org>
> Subject: Re: [Haskell-beginners] Monadic functions definitions for
> free monadic DSL
> Message-ID:
> <CAPY+ZdQfO_+42BGYd2zAL6bvdgQuCadjgADj0T_
> 7C7ogk-Xvpg at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Dear Sumit,
>
> You are right that there's something's fishy about the free monadic
> modeling of accept.
>
> The following parallel construction will prove instructive:
>
> The native effect:
>
> send :: chan -> ByteString -> IO Bool
>
> is modeled in the free monad by the constructor for the base functor
>
> Send :: chan -> ByteString -> (Bool -> next) -> NetworkActivity chan
> next
>
> which is the data wrapping used in the value level
>
> sendit :: chan -> ByteString -> Free (NetworkActivity chan) Bool
> sendit chan buf = liftF (Send chan buf identity)
>
> Analogously, the native
>
> accept :: chan -> IO chan
>
> is modeled by
>
> Accept :: chan -> (chan -> next) -> NetworkActivity chan next
>
> used in
>
> acc :: chan -> Free (NetworkActivity chan) chan
> acc chan = liftF (Accept chan identity)
>
> Except that you used a different constructor for the base functor. Not
>
> Accept :: chan -> (chan -> next) -> NetworkActivity chan next
>
> but
>
> Accept :: chan -> next -> (chan -> next) -> NetworkActivity chan next
>
> which is equivalent to
>
> Accept :: chan -> (Maybe chan -> next) -> NetworkActivity chan next
>
> The new free monadic term that substitutes for the native accept is the
> same like before
>
> acc chan = liftF (Accept chan identity)
>
> only with a different type
>
> acc :: chan -> Free (NetworkActivity chan) (Maybe chan)
>
> modeling a native
>
> accept :: chan -> IO (Maybe chan)
>
> Given a native API, its free monad encoding is entirely boilerplate. I
> wrote about the boilerplate process here (skip the sections that don't
> concern you):
>
> http://www.atamo.com/articles/free-monads-wont-detox-your-colon/
>
> Best, Kim-Ee
>
> -- Kim-Ee
>
> On Fri, Oct 14, 2016 at 6:44 AM, Sumit Raja <sumitraja at gmail.com> wrote:
>
> > > I would really like to help you, but without your imports, packages,
> etc,
> > > it is really hard to interpret your program. Like where does
> decodeUtf8
> > > come from, or receive, or TCPSocket? If they are functions you wrote,
> I
> > > don't need their code, the types would be sufficient.
> > >
> > Imports are:
> >
> > import Protolude
> > import Control.Monad.Free
> > import System.Socket
> > import System.Socket.Family.Inet
> > import System.Socket.Type.Stream
> > import System.Socket.Protocol.TCP
> > import Control.Exception ( bracket, catch )
> > import Data.ByteString as BS (uncons)
> >
> > decodeUtf8 :: ByteString -> Text
> > encodeUtf8 :: Text -> ByteString
> >
> > I'm using the socket library for the actual networking
> > (https://hackage.haskell.org/package/socket-0.6.0.1)
> >
> > type TCPSocket = Socket Inet Stream TCP
> > receive :: Socket f t p -> Int -> MessageFlags -> IO ByteString
> Source
> > send :: Socket f t p -> ByteString -> MessageFlags -> IO Int
> > accept :: (Family f, Storable (SocketAddress f)) => Socket f t p
> > -> IO (Socket f t p, SocketAddress f)
> >
> > If it helps the full source is at
> > https://bitbucket.org/sumitraja/network-free/src/
> > a4fcbc74c9e178e81d8b10b60d912b32c542b661/src/Lib.hs.
> >
> > Looking forward to your assistance.
> >
> > Thanks
> >
> > Sumit
> > _______________________________________________
> > Beginners mailing list
> > Beginners at haskell.org
> > http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
> >
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> End of Beginners Digest, Vol 100, Issue 14
> ******************************************
>
--
Best Regards,
Boon Hui
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