[Haskell-cafe] A small step towards solving cabal hell.

timothyhobbs at seznam.cz timothyhobbs at seznam.cz
Sun Nov 18 14:33:14 CET 2012

I've read a lot of negative regarding the problems with cabal and hackage.
I've written quite a few of them myself.

I want to propose a simple change in philosophy of packages.

Haskell has inherited a philosophy from the imperative world,
that there are two types of packages:
Libraries and applications.

Libraries are big collections of modules.
Applications are big collections of modules.

There is a difference from the perspective of the build system.  

Applications are big collections of modules that belong together and 
mutually rely upon each other for the application to work. Such that if one 
module is missing, the application cannot build and thus cannot do useful 
tasks.  If an application doesn't build, then the maintainer has to go and 
fix that problem.  This isn't perfect, I do not solve this problem in this 

Libraries don't always have this property.
For example, XMonad.Layout.Column
has no mutual dependency on XMonad.Layout.Circle

This is a feature of libraries that can and should be taken advantage of 
wherever possible :)

We can and should,
break up libraries into "books".

I hold this opinion,
because libraries are hard to maintain.

If xmonad-contrib refuses to build,
I open up it's source code,
and see some hundred modules.

I cannot,
as a non-xmonad developer,
imagine myself fixing such a large library.
But if it was just one small module from that library I wanted,
and it refused to build,
and I opened it up,
and there were just 3 files there.
I wouldn't feel so overwhelmed.

I would fix the problem myself.

What I'm trying to say,
is that "books"
(small packages containing 3 modules or less)
are so easy to maintain,
that they really need no maintainer at all.
Any idiot can fix one.

But libraries,
with their hundreds of modules,
and seemingly endless dependencies,
Can be much harder to maintain,
and require a knowledgeable maintainer.

So lets stop publishing libraries,
and maintaining libraries,
and listening to people crying when libraries don't build,
and lets start writing books,
and publishing really small packages,
that are so simple anyone can fix them when they break
even when they have no in depth knowledge of the package.

Lets make a new guideline for "libraries"
that if it is possible to split a library into two or more,
non-mutually dependent parts,
than we *should* split them such.



I noticed that yesod is already a collection of "books",
but it appears to me, that these packages are STILL mutually dependent :(
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