Fwd: Is anything being done to remedy the soul crushing compile times of GHC?

Tuncer Ayaz tuncer.ayaz at gmail.com
Wed Feb 17 13:31:39 UTC 2016

On 17 February 2016 at 07:40, Evan Laforge <qdunkan at gmail.com> wrote:

> My impression from the reddit thread is that three things are going
> on:
> 1 - cabal has quite a bit of startup overhead
> 2 - ghc takes a long time on certain inputs, e.g. long list literals.
> There are probably already tickets for these.

In my experience GHC startup overhead (time) has increased quite a lot
somewhere in 7.x. I don't know if it's the cause, but perhaps dyn libs
may be part of the reason. I'm not sure because I once (7.8 I believe)
tried to build without dynlink support and couldn't measure a
substantial improvement.

So, if you start ghc(i) for the first time from a spinning disk, it's
very noticeable and quite a delay. Once it's cached, it's fast, so I
think it's primarily due to reading stuff from disk.

Just to mention the ideal overhead: anything below 400ms is small
enough to not disrupt the flow and feels responsive. Go over 1s and it

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