GHC Weekly News - 2015/05/11

Austin Seipp austin at
Mon May 11 14:51:23 UTC 2015

(This post is available online at

Hi *,

It's been a few weeks since the last news bulletin - this is the
result of mostly quietness on behalf of the list and developers, and
some sickness on behalf of your editor for several days there. But now
there's actually some things to write here!

The past few weeks, GHC HQ has been having some quiet meetings mostly
about bugfixes for a 7.10.2 release - as well as noodling about
compiler performance. Austin has begun compiling his preliminary notes
on the wiki, under the [wiki:CompilerPerformance] page, where we'll be
trying to keep track of the ongoing performance story. Hopefully, GHC
7.12.1 will boast a bit better performance numbers.

There are a lot of users who are interested in this particular pain
point, so please file tickets and CC yourself on bugs (like #10370),
or feel free to help out!

== 7.10.2 status ==

There's been a bit of chatter about the lists about something on many
peoples mind: the release of GHC 7.10.2. Most prominently, Mark
Lentczner popped in to ask when the next GHC release will happen - in
particular, he'd like to make a Haskell Platform release in lockstep
with it (see below for a link to Mark's email).

Until recently, the actual desire for 7.10.2 wasn't totally clear, and
at this point, GHC HQ hasn't firmly committed to the 7.10.2 release
date. But if milestone:7.10.2 is any indicator, we've already closed
over three dozen bugs, several of them high priority - and they keep
coming in. So it seems likely people will want these fixes in their
hands relatively soon.

Just remember: '''if you need a fix for 7.10.2''', or have a bug you
need us to look at, please email the `ghc-devs` list, file a ticket,
and get our attention! Just be sure to set the milestone to 7.10.2.

== List chatter ==

  - Herbert Valerio Riedel opened an RFC about a regression in GHC
7.10 relating to the update to Unicode 7. Any input from users of
international languages or unicode users would be appreciated!

  - Herbert Valerio Riedel also asked about a new C pre-processor
implementation for GHC - but in particular, adopting the extant
`cpphs` into the GHC codebase for this task itself.

  - Austin Seipp emailed `ghc-devs` about the HCAR report, for which
the GHC entry is due May 17th! Developers should get their edits in

  - Joachim Breitner asks if the branchless implementation for our
literal cases are worth it for their complexity. There were some
interesting responses, including some remarks on the V8 JavaScript

  - Niklas Hambüchen announced that he's backported the recent
lightweight stack-trace support in GHC HEAD to GHC 7.10 and GHC 7.8 -
meaning that users of these stable release can have informative call
stack traces, even without profiling! FP Complete was interested in
this feature, so they'd probably love to hear user input.

  - David Terei has written up a proposal on reconciling the existence
of Roles with Safe Haskell, which caused us a lot of problems during
the 7.8 release cycle. In particular, concerning the ability to break
module abstractions and requiring programmers to safeguard
abstractions through careful use of roles - and David's written a
proposal to address that.

  - Mark Lentczner started a thread about the 7.10.2 release schedule
- because this time, he wants to do a concurrent Haskell Platform
release! The thread ended up with a good amount of discussion
concerning if 7.10.2 is even needed - but at this rate, it looks like
it will ship sometime soon.

  - Mateusz Kowalczyk posted to `ghc-devs` hoping to get some help
with a tricky, long-standing issue: #4012, which concerns the
determinism of GHC binaries. It turns out GHC isn't entirely
deterministic when it calculates package IDs, meaning things get
really bad when you mix prebuilt binary packages for systems. This in
particular has become a real problem for the Nix package manager and
users of Haskell applications. Mateusz asks if anyone would be willing
to help look into it - and a lot of people would appreciate the help!
== Noteworthy commits ==

 - Commit f2d1b7fcbbc55e33375a7321222a9f4ee189aa38 - Support unboxing
for GADT product types.

 - Commit 51af102e5c6c56e0987432aa5a21fe10e24090e9 - Better hints when
RTS options are not available.

 - Commit 524ddbdad5816f77b7b719cac0671eebd3473616 - Make sure
`GHC.List.last` is memory-efficient.

 - Commit a1275a762ec04c1159ae37199b1c8f998a5c5499 - Improve
improvement in the constraint solver.

 - Commit 4efa421327cf127ebefde59b2eece693e37dc3c6 - Permit empty
closed type families.

 - Commit 477f514f6ebcf783810da93e2191e4b6ea65559b - rts: add
"-no-rtsopts-suggestions" option

 - Commit cf7573b8207bbb17c58612f3345e0b17d74cfb58 - More accurate
allocation stats for :set +s

 - Commit c4e8097ea8dd6e43eae7aadd6bae7e13272ba74d - Bump base version
to ``

 - Commit 0bbc2ac6dae9ce2838f23a75a6a989826c06f3f5 - Use the gold
linker for aarch64/linux (#9673)

 - Commit 1e8c9b81a819da8eb54405a029fc33a9f5220321 - Enable SMP and
GHCi support for AArch64

== Closed tickets ==

#10293, #10273, #10021, #10209, #10255, #10326, #9745, #10314, #8928,
#8743, #10182, #10281, #10325, #10297, #10292, #10304, #10260, #9204,
#10121, #10329, #9920, #10308, #10234, #10356, #10351, #10364, #9564,
#10306, #10108, #9581, #10369, #9673, #10288, #10260, #10363, #10315,
#10389, #9929, #10384, #10382, #10400, #10256, #10254, #10277, #10299,
#10268, #10269, #10280, #10312, #10209, #10109, #10321, #10285, #9895,
#10395, #10263, #10293, #10210, #10302, #10206, #9858, #10045, and


Austin Seipp, Haskell Consultant
Well-Typed LLP,

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