Compilation time

Matthew Pickering matthewtpickering at
Tue Jul 4 07:31:27 UTC 2017

I tried the package with 8.2.1 and 8.0.2 and both build in less than 5
seconds with quite a large amount of variability. As Robin points out,
there are varying factors which can account for longer build times on

On Tue, Jul 4, 2017 at 8:16 AM, Deest, Gaël <gael.deest at> wrote:
> Hi all,
> As you are probably well aware, GHC performance has been a growing concern
> over the last few years. Many Haskell programmers complain that build time
> has significantly increased over the last few releases. However, to our
> knowledge, there isn't much data available to substantiate this claim and
> the severity of these problems is not well known.
> That's why we would like to bring some anecdotal evidence to your attention
> that seems to indicate really major performance regressions. We stumbled
> upon the CI of the data-reify package, which is built against all GHC
> releases since 2010 :
> tl;dr: Build time has gone from 1 min 32s for GHC 7.0 to 4 min 35s for GHC
> 8.2. The 8.2 release alone seems to have increased compilation time by
> almost 2 minutes, with the current development branch bringing only minor
> performance improvements.
> Of course, this single data point is not sufficient to establish how severe
> and widespread these problems are. More data could probably be gathered from
> other packages. However, it certainly matches our (subjective) experience
> and we felt important to report it to you.
> Regards,
> --
> Gaël Deest
> Tweag I/O
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