[Haskell-cafe] Re: [Haskell] ANN: NoSlow - Microbenchmarks for array libraries

[Duncan Coutts]

On Sat, 2009-11-28 at 20:13 +0100, Henning Thielemann wrote:

> However I have still the problem, that once criterion is installed
> without gtk and cairo, then 'cabal install' still wants to download them
>  when I install packages that import 'criterion'. :-( Bug or feature?

That's a problem with the cabal-install resolver. When configuring
criterion it optimistically assumes that it will be able to install the
optional dependencies. I've been working on an extra bottom-up pass for
the resolver that will prune packages that cannot possibly be installed.
That should help in this case and for the more common case of packages
that need a particular version of base.

In the mean time, a workaround would be to try:
$ cabal install noslow criterion -f-chart --dry-run

That should make it select criterion without the chart dep, and since
the deps of criterion will then not change it should end up picking the
installed instance of criterion rather than rebuilding it.

Another thing that'd help here, but isn't implemented, is "installed"
constraints. So that you could ask it commit to using the installed
instance of criterion, rather than it having the option to rebuild
(which in general it needs so it can get consistent deps).

Duncan