On 29/08/2008, at 01:31, Simon Marlow wrote:
Roman Leshchinskiy wrote:
On 28/08/2008, at 23:59, Simon Marlow wrote:
The important thing about Cabal's way of specifying dependencies
is that they can be made sound with not much difficulty. If I say
that my package depends on base==3.0 and network==1.0, then I can
guarantee that as long as those dependencies are present then my
package will build. ("but but but..." I hear you say - don't
touch that keyboard yet!)
Suppose you used autoconf tests instead. You might happen to know
that Network.Socket.blah was added at some point and write a test
for that, but alas if you didn't also write a test for
Network.Socket.foo (which your code uses but ends up getting
removed in network-1.1) then your code breaks. Autoconf doesn't
help you make your configuration sound, and you get no prior
guarantee that your code will build.
Cabal doesn't give this guarantee, either, since it allows you to
depend on just network or on network>x.
Indeed. That's why I was careful not to say that Cabal gives you
the guarantee, only that it's easy to achieve it.
True, it's easy to specify. But IIUC, if you do so you have to update
your package whenever any of the packages you depend on changes even
if that change doesn't affect you. This is a very high (if not
prohibitive) cost and one which the autoconf model doesn't force on you.
Both systems are flawed, but neither fundamentally. For Cabal I
think it would be interesting to look into using more precise
dependencies (module.identifier::type, rather than package-
version) and have them auto-generated. But this has difficult
implications: implementing cabal-install's installation plans
becomes much harder, for example.
Interesting. From our previous discussion I got the impression that
you wouldn't like something like this. :-)
Sorry for giving that impression. Yes I'd like to solve the
problems that Cabal dependencies have, but I don't want the solution
to be too costly - first-class interfaces seem too heavyweight to
me. But I do agree with most of the arguments you gave in their
favour.
I'm not sure what you mean by first-class interfaces. Surely, if you
specify the interfaces you depend on you'll want to share and reuse
those specifications.
Roman
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