some mails that accidentally did not make it to the list
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Excerpts from Florian Friesdorf's message of Sat Sep 24 15:19:06 +0200 2011:
> I prefer a "manually" maintained tree over on-the-fly. Having explicit
> nix expressions allows for somebody/something to test these and building
> a database of known good sets of packages. If we generate the
> expressions on-the-fly, we would need a database of checksums in order
> to know whether the on-the-fly generated expressions are what we want
> them to be (as brought up by Michael).
If you mantain them manually you
- miss to remove dependencies even if they got dropped unless you
regenerate everything
- you may run into some cases where dependencies depend on cabal flags
or versions of other packages being used. Obviously it doesn't matter
much in practise (anymore?) else Peter would have had more issues.
- you may start builds which then might fail due to wrong versions being
passed (either ghc or library versions).
using hack-nix you update the hack-nix cache. You define which C
libraries to pass. Everything else should be automatic (dependency
resolution etc). Brute force is used. So it only works on "limited
package list such as _latest packages_".
It fails early. Eg it says "no version of X found but 2.0 required".
Current drawback: requires more evaluation time. Colud be fixed by using
haskell or C implementation.
You can easily construct artificial dependency construct which can not
be mapped to what Peter does. However because most other distros have
similar limitations it looks like people work hard on avoid such
scenarios so it may not matter that much for most common packages.
That's a short list. You can overwrite arbitrary cabal flags on the fly
which also may lead to many changes in dependencies. hack-nix copes with
it - if you generate .nix files it may force you regenerating a new pool
of .nix files (worst case). Again: it doesn't seem to happen often
enough to care about.
Marc Weber
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Florian Friesdorf <f...@chaoflow.net>
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