Build system idea

Simon Marlow marlowsd at
Thu Aug 28 11:31:22 EDT 2008

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 
>> (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.

>> 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.


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