gale at sefer.org
Sun Jan 1 13:11:41 CET 2012
>> Today, it is very unusual to use GHC by itself.
>> To use Haskell, you install the Haskell Platform.
>> That is GHC together with Cabal and a basic
>> set of libraries. It is very easy to install.
Wolfram Kahl wrote:
> However, since you are willing and able to test bleeding-edge versions of GHC,
> you need to be able to live without the platform, which typically
> catches up to GHC versions only within a couple of months.
It's true that the platform provides a stable version of GHC,
as needed by most people, not the bleeding edge. But even if you need
GHC HEAD you would typically use cabal. Unless for some reason
you need to shuffle around manually the various pieces that get built,
of package dependencies manually, etc. There are some people
who need to do it, and it is doable, though much more
complicated and error-prone than just using cabal.
>> Almost all Haskell software is expected to
>> be installed using Cabal nowadays.
> It is important to know that people associate two packages
> with the name ``Cabal''
They are closely interconnected though. If you use the platform,
that distinction is not very important. It just works.
> Life without cabal-install is not only possible,
> but also safer.
I disagree with that. Manual processes are error-prone.
With experience, you can learn how
to do things totally manually, just like you can learn to
build C projects manually without make, and with even
more experience, you can learn to avoid all of the
pitfalls. It's a good thing to know, but I wouldn't put
it at first priority unless there's a special reason for it.
> (See also: http://www.vex.net/~trebla/haskell/sicp.xhtml )
The Cabal system is quite mature now, but still far
from perfect. Problems can arise. Most of the problems
are inherent to the "DLL Hell" that can occur in any
separate compilation system, and some arise from the fact
that Cabal's dependency solver needs improvement (that's
a hard problem).
That link is a detailed write-up of just about everything
that can possibly go wrong. In my experience, none of that
happens until you've been using an installation for a long time,
or if you are very trigger-happy with upgrading packages to the latest
version for no reason. Or if you're using a package with a huge amount
of fast-changing dependencies, like one of the web frameworks.
Even then, it's almost always easy enough just to re-install the
platform to get a fresh install. Your next few compiles will take a
few minutes longer as some packages get rebuilt, but that's about it.
To avoid that altogether, I use cabal-dev. This allows me to
build a package I am working on in a sandbox with just the
dependencies it needs, tailored exactly for the needs
of my specific package. Cabal-dev also makes it
easy to experiment with how users will experience
building my package.
It's good to know all the intricacies of the build system,
and what is happening beneath the surface if it gets
lost. The linked article is a worthwhile read for that.
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