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Today's Topics:
1. Re: database question (Brent Yorgey)
2. Re: The cost of generality, or how expensive is realToFrac?
(Daniel Fischer)
----------------------------------------------------------------------
Message: 1
Date: Sun, 19 Sep 2010 22:34:28 -0400
From: Brent Yorgey <byor...@seas.upenn.edu>
Subject: Re: [Haskell-beginners] database question
To: beginners@haskell.org
Message-ID: <20100920023428.ga9...@seas.upenn.edu>
Content-Type: text/plain; charset=us-ascii
On Sun, Sep 19, 2010 at 07:53:54PM -0400, Brandon S Allbery KF8NH wrote:
> Since IO must always be at the base(*) of any stack of monad transformers it
> is used in, the MonadIO class provides a convenience function liftIO that
> lifts its argument directly to the IO monad without having to step through
> any intermediates.
>
> _______
> * we call it "lifting" but we also claim IO is at the base of the stack, and
> I at least usually expect a base to be at the bottom. Nice and
> confusing :)
I think of liftIO as lifting its argument *from* the IO monad (at the
bottom of the stack) into a monad higher up the stack.
liftIO :: (MonadIO m) => IO a -> m a
So I don't find it confusing/backwards at all.
-Brent
------------------------------
Message: 2
Date: Mon, 20 Sep 2010 16:53:25 +0200
From: Daniel Fischer <daniel.is.fisc...@web.de>
Subject: Re: [Haskell-beginners] The cost of generality, or how
expensive is realToFrac?
To: Greg <gregli...@me.com>, beginners@haskell.org
Message-ID: <201009201653.26350.daniel.is.fisc...@web.de>
Content-Type: text/plain; charset="utf-8"
On Monday 20 September 2010 05:09:16 you wrote:
> I'm building with the latest Haskell Platform. Â GHC 6.12.3 and OpenGL
> 2.2.1.1
:sigh:
So we can forget about rewrite rules, newtypes, unsafeCoerce and all that
Jazz.
In OpenGL-2.2.1.1, GLclampf (and GLfloat &c.) were not newtypes, they were
type synonyms,
type GLclampf = Float
and so on.
So it's clear that GHC rewrites realToFrac to double2Float# in the
benchmark, since it's converting to Float (that also explains the absence
of casts in your core).
Then, if floatToFloat is faster than realToFrac in your programme (compiled
with optimisations), that probably means GHC doesn't spot an opportunity to
replace realToFrac with double2Float# because the types are still
polymorphic. Perhaps some type annotations would help.
------------------------------
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