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Today's Topics:
1. Re: reading lines with history from bash terminal in OS X
(Dennis Raddle)
----------------------------------------------------------------------
Message: 1
Date: Tue, 2 Aug 2016 12:24:31 -0700
From: Dennis Raddle <dennis.rad...@gmail.com>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] reading lines with history from bash
terminal in OS X
Message-ID:
<CAKxLvooJb3O=67re=tRR0ZH_-v=zqgr9eut+twvle7swlo-...@mail.gmail.com>
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Thanks. I will study this.
On Mon, Aug 1, 2016 at 5:43 AM, David McBride <toa...@gmail.com> wrote:
> MonadIO m => MonadIO (InputT m)
> MonadException m => MonadException (InputT m)
>
> MonadIO means you have access to liftIO. liftIO . evaluate . force $
> mycode.
> MonadException means that you have access to haskeline's exception
> catching mechanisms.
>
> In System.Console.Haskeline.MonadException, you have the catch, catches,
> and handle functions which will allow you to catch IO exceptions (in
> combination with liftIO), and also a bracket which will just let you do
> arbitrary IO actions and clean up when you are done (or hit an exception).
>
> >let mycode = undefined :: Handle -> IO () -- example code
>
> runInputT _ (bracket (liftIO $ openFile "blah" ReadMode) (liftIO . hClose)
> (\fp -> liftIO . mycode $ fp))
>
> Another way to use it might be
>
> runInputT _ (liftIO $ mycode _) `catches` [Handler iohandler, Handler
> anotherhandler]
> where
> iohandler :: IOException -> IO ()
> iohandler e = putStrLn "got io exception" >> return ()
>
> Exceptions are always a pain, and so are transformers, but you get used to
> them.
>
> On Mon, Aug 1, 2016 at 4:06 AM, Dennis Raddle <dennis.rad...@gmail.com>
> wrote:
>
>> I'm looking over haskeline. It looks like I have to modify some of my
>> code that is in the IO monad right now. I use 'evaluate' in several places,
>> and also 'evaluate $ force', to make sure that IO exceptions are
>> encountered where I can catch them. Can I use 'evaluate' with InputT? I'm
>> muddled headed about what to do. I guess I would lift 'evaluate' into the
>> inner monad? I am not sure what those words mean. How would I catch IO
>> exceptions?
>>
>> On Thu, Jul 28, 2016 at 5:35 PM, Dennis Raddle <dennis.rad...@gmail.com>
>> wrote:
>>
>>> Thanks. I'll install haskeline
>>>
>>> On Thu, Jul 28, 2016 at 5:05 PM, David McBride <toa...@gmail.com> wrote:
>>>
>>>> You will have to use the haskeline library. FYI that is the library
>>>> that makes ghci work.
>>>>
>>>> On Thu, Jul 28, 2016 at 6:09 PM, Dennis Raddle <dennis.rad...@gmail.com
>>>> > wrote:
>>>>
>>>>> I wrote a program first in Windows, where it works as expected, and
>>>>> now I'm using it in OS X and getting undesired behavior.
>>>>>
>>>>> It reads lines from the terminal using the getLine function. In
>>>>> Windows (DOS, actually) the up and down arrows can be used to choose
>>>>> previously entered lines. However, this does not work in bash in OS X.
>>>>>
>>>>> What do I need to get the history available via the arrow keys?
>>>>>
>>>>> D
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> Beginners mailing list
>>>>> Beginners@haskell.org
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>>>>>
>>>>>
>>>>
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>>>
>>
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>
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