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Today's Topics:
1. Re: Haskell on Debian (Brent Yorgey)
2. Re: Lens and imperative programming (Darren Grant)
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Message: 1
Date: Fri, 24 May 2013 14:15:16 -0400
From: Brent Yorgey <[email protected]>
Subject: Re: [Haskell-beginners] Haskell on Debian
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset=us-ascii
On Fri, May 24, 2013 at 06:45:28PM +0200, Giacomo Tesio wrote:
> Can I use cabal install without being root?
>
> I'd like to use packages from hackage instead of those provided by apt-get
> as far as possibile.
> Is it possible at all? I guess that libraries depending on FFI won't
> works...
In fact, you *should only* use cabal install without being root. If
you ever have to write "sudo cabal install ..." you are doing
something wrong.
Libraries depending on FFI will work fine. Cabal cannot automatically
install external (non-Haskell) dependencies, so you must install any
such dependencies yourself (using apt-get) before calling cabal
install. Of course, you will probably have to run apt-get with sudo.
-Brent
------------------------------
Message: 2
Date: Fri, 24 May 2013 12:57:12 -0700
From: Darren Grant <[email protected]>
Subject: Re: [Haskell-beginners] Lens and imperative programming
To: Haskell Beginners <[email protected]>
Message-ID:
<CA+9vpFdDukQ-GfJzWpfQy8-B=-3esgnnyvm7gzrppnuaohx...@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"
+= carries expectation of specific behavioural properties in popular
circles, making it a devious moniker. In an attempt to bridge programming
paradigms with Haskell this problem is common. There be dragons here:
Always question your assumptions about familiar names and symbols.
On 2013-05-24 11:15 AM, "Brent Yorgey" <[email protected]> wrote:
> On Fri, May 24, 2013 at 06:41:27PM +0200, Giacomo Tesio wrote:
> > For example I'm scared by += a function compositions.
> >
> > For example here
> >
> > units.traversed.health -= 3
> >
> >
> > (from
> >
> http://www.haskellforall.com/2013/05/program-imperatively-using-haskell.html
> )
> > I've some difficult to grasp the type. I can calculate it (or ask ghci
> :-D)
> > , but it looks complex to grasp.
> >
> > May be I'm just too new to Haskell tools... but... I fear that in the
> long
> > run, this could become unreadable.
>
> You could already do exactly the same thing without the lens package.
> It uses the State monad. The lens package just makes it much simpler
> to write this code.
>
> If you think that overuse of the State monad will lead to bad,
> unmaintainable code, you are right. But that has nothing to do with
> lenses.
>
> Lenses can also be used in many contexts which do not involve the
> State monad.
>
> -Brent
>
> _______________________________________________
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