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Today's Topics:
1. gtk2hs and threadDelay (ga...@caesar.elte.hu)
2. Getting the current system date outside the IO Monad
(AbdulSattar Mohammed)
3. Re: Getting the current system date outside the IO Monad
(Chadda? Fouch?)
----------------------------------------------------------------------
Message: 1
Date: Mon, 26 Dec 2011 14:24:52 +0100
From: ga...@caesar.elte.hu
Subject: [Haskell-beginners] gtk2hs and threadDelay
To: beginners@haskell.org
Message-ID: <20111226142452.10493mg6jdffn...@webmail.caesar.elte.hu>
Content-Type: text/plain; charset=ISO-8859-2; DelSp="Yes";
format="flowed"
Hello!
I managed to do it with timeoutAdd:
--code below is the onClicked function:
drawProgram gui preprocPrg = do
let drArea = (drawWin gui)
drw <- widgetGetDrawWindow drArea
-- let list = compileToList preprocPrg
-- renderWithDrawable drw (drawFromList list)
renderWithDrawable drw (myDraw 200 200)
-- drawWindowProcessUpdates drw True
timeoutAdd ((\_ -> do
renderWithDrawable drw (myDraw2 200 200)
return False) 5) 500
return ()
But "sometimes" it gives the following error:
(<interactive>:23929): Gdk-WARNING **: Using Cairo rendering requires
the drawable argument to
have a specified colormap. All windows have a colormap,
however, pixmaps only have colormap by default if they
were created with a non-NULL window argument. Otherwise
a colormap must be set on them with gdk_drawable_set_colormap
(<interactive>:23929): Gdk-CRITICAL **: IA__gdk_cairo_region:
assertion `region != NULL' failed
<interactive>: user error (NULL pointer)
<interactive>: interrupted
<interactive>: warning: too many hs_exit()s
What can cause this? I think the other parts of my program are
correct, and I cant understand, how can ghci "randomly give" this
error. (every 5. try)
To be honest, my goal is to make a "turtle graphics" program, so I ll
have to write a function, which draws a line on the GUI in slow
motion: there will be even more problems with timing, because I ll
have to draw the line pixel by pixel.
------------------------------
Message: 2
Date: Tue, 27 Dec 2011 14:11:34 +0530
From: AbdulSattar Mohammed <codingta...@gmail.com>
Subject: [Haskell-beginners] Getting the current system date outside
the IO Monad
To: beginners@haskell.org
Message-ID:
<ca+mxqh_oofa7u5dgg_let6cwfncmqpaonudiy9di63x+6dg...@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"
I'm still learning Haskell and I've started learning Yesod. I pretty much
built a blog before I came this silly roadblock.
Whenever I create a new post, I want it take the current system time as its
creation time. I understand it's an impure operation and it must go into
the IO Monad to be performed. But, in Yesod, your handler is of the type
Handler RepHtml. I don't get how you could get the impure value into a pure
function without main playing any part.
Here's the link for my blog: http://hpaste.org/55757#line85
--
Warm Regards,
AbdulSattar Mohammed
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Message: 3
Date: Tue, 27 Dec 2011 09:53:08 +0100
From: Chadda? Fouch? <chaddai.fou...@gmail.com>
Subject: Re: [Haskell-beginners] Getting the current system date
outside the IO Monad
To: AbdulSattar Mohammed <codingta...@gmail.com>
Cc: beginners@haskell.org
Message-ID:
<canfjzryn-vkzxji_st5p2j_wbo-alafq4ha9k49-fkubj8p...@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
On Tue, Dec 27, 2011 at 9:41 AM, AbdulSattar Mohammed
<codingta...@gmail.com> wrote:
> I'm still learning Haskell and I've started learning Yesod. I pretty much
> built a blog before I came this silly roadblock.
>
> Whenever I create a new post, I want it take the current system time as its
> creation time. I understand it's an impure operation and it must go into the
> IO Monad to be performed. But, in Yesod, your handler is of the type Handler
> RepHtml. I don't get how you could get the impure value into a pure function
> without main playing any part.
>
Thankfully, we can build monad "stacks" that contains several
capacities, this is a standard way to design libraries in Haskell.
Yesod use Handler and not IO because it needs to convey more
informations than just the IO monad but Handler normally contains IO
and is as such a MonadIO instance. In other words, you can use any IO
action with the "liftIO" function.
--
Jeda?
------------------------------
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