Proposal: end lazy IO results with errors/exceptions

[Roman Cheplyaka]

Agreed, this sounds like a great idea.

* Joachim Breitner <mail at joachim-breitner.de> [2014-07-21 22:21:43+0200]
> Hi,
> 
> superficially¹ +1
> 
> Joachim
> 
> ¹ I like the idea, but can’t tell what the downsides are.
> 
> 
> Am Montag, den 21.07.2014, 16:16 -0400 schrieb David Feuer:
> > Currently,
> > 
> > withFile "foo" hGetContents >>= putStrLn
> > 
> > prints out an empty line, the better to confuse newbies.
> > 
> > I propose modifying the lazyRead function in GHC.IO.Handle.Text that
> > currently reads
> > 
> > lazyRead :: Handle -> IO String
> > lazyRead handle =
> >    unsafeInterleaveIO $
> >         withHandle "hGetContents" handle $ \ handle_ -> do
> >         case haType handle_ of
> >           ClosedHandle     -> return (handle_, "")
> >           SemiClosedHandle -> lazyReadBuffered handle handle_
> >           _ -> ioException
> >                   (IOError (Just handle) IllegalOperation "hGetContents"
> >                         "illegal handle type" Nothing Nothing)
> > 
> > to something like
> > 
> > lazyRead :: Handle -> IO String
> > lazyRead handle =
> >    unsafeInterleaveIO $
> >         withHandle "hGetContents" handle $ \ handle_ -> do
> >         case haType handle_ of
> >           ClosedHandle     -> return (handle_, error "Forcing the
> > result of a lazy read led to an attempt to read from a closed
> > handle.")
> >           SemiClosedHandle -> lazyReadBuffered handle handle_
> >           _ -> ioException
> >                   (IOError (Just handle) IllegalOperation "hGetContents"
> >                         "illegal handle type" Nothing Nothing)
> > 
> > Ideally that error should instead be something to throw an imprecise
> > exception, but I don't know how to use those yet. I can't personally
> > see a way for this to break sane, working code, but the folks on #ghc
> > thought it should be discussed and debated on list.
> > 
> > David Feuer
> > _______________________________________________
> > Libraries mailing list
> > Libraries at haskell.org
> > http://www.haskell.org/mailman/listinfo/libraries
> > 
> 
> -- 
> Joachim Breitner
>   e-Mail: mail at joachim-breitner.de
>   Homepage: http://www.joachim-breitner.de
>   Jabber-ID: nomeata at joachim-breitner.de
> 



> _______________________________________________
> Libraries mailing list
> Libraries at haskell.org
> http://www.haskell.org/mailman/listinfo/libraries

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 819 bytes
Desc: Digital signature
URL: <http://www.haskell.org/pipermail/libraries/attachments/20140722/edd7b436/attachment.sig>