Posts for the month of February 2015

GHC Weekly News - 2015/02/23

Hi *,

It's once again time for your sometimes-slightly-irregularly-scheduled GHC news! This past Friday marked the end of the FTP vote for GHC 7.10, there's an RC on the way (see below), we've closed out a good set of patches and tickets from users and pushed them into HEAD, and to top it off - it's your editor's birthday today, so that's nice!

Quick note: as said above GHC HQ is expecting to make a third release candidate for GHC 7.10.1 soon in early March since the delay has allowed us to pick up some more changes and bugfixes. We plan on the final release being close to the end of March (previously end of February).

This week, GHC HQ met up again to discuss and write down our current priorities and thoughts:

  • After discussing our current timetable - as we're currently hovering around the ICFP deadline - we're hoping to make our third GHC 7.10.1 release candidate on Friday, March 13th, with the final release on Friday, March 27th. This was the main take away from our meeting today.

We've also had a little more list activity this week than we did before:

Some noteworthy commits that went into ghc.git in the past week include:

Closed tickets the past week include: #9266, #10095, #9959, #10086, #9094, #9606, #9402, #10093, #9054, #10102, #4366, #7604, #9103, #10104, #7765, #7103, #10051, #7056, #9907, #10078, #10096, #10072, #10043, #9926, #10088, #10091, #8309, #9049, #9895, and #8539.

GHC Weekly News - 2015/02/17

Hi *,

It's time for the GHC weekly news. It's been particularly quiet the past week still, and the ghc-7.10 branch has been quite quiet. So the notes are relatively short this week.

This week, GHC HQ met up to discuss some new stuff:

  • Most of the discussion this week was about particular bugs for GHC 7.10, including getting some tickets fixed like #10058, #8276, and #9968.
  • Since the 7.10 release is getting close, we'll be starting up a new status page about GHC 7.12 (and probably get started writing things for the HCAR report in May) and what our plans are soon. Watch this space!

As usual, we've had a healthy amount of random assorted chatter on the mailing lists:

Some noteworthy commits that went into ghc.git in the past week include:

Closed tickets the past week include: #10047, #10082, #10019, #10007, #9930, #10085, #10080, #9266, #10095, and #3649.

GHC Weekly News - 2015/02/10

Hi *,

Welcome! This is the first GHC Weekly news of February 2015. You might be wondering what happened to the last one. Well, your editor was just in New York for the past week attending Compose Conference, making friends and talking a lot about Haskell (luckily we missed a snow storm that may have messed it up quite badly!)

The conference was great. I got to have some interesting discussions about GHC and Haskell with many friendly faces from all around at an incredibly well run conference with a stellar set of people. Many thanks to NY Haskell (organizing), Spotify (hosting space), and to all the speakers for a wonderful time. (And of course, your editor would like to thank his employer Well-Typed for sending him!)

But now, since your author has returned, GHC HQ met back up this week for some discussion, with some regularly scheduled topics. For the most part it was a short meeting this week - our goals are pretty well identified:

  • It's likely GHC HQ will do a third 7.10.1 Release Candidate at the very end of February after the votes are included. We missed some patches in RC2 (such as Phab:D347) and incorporated even more bugfixes, so this is worth a test drive by users.
  • For the most part, things for 7.10 have been going very smoothly other than the debates and a few bugs trickling in - there has not been much ticket activity the past two weeks, so things feel pretty good right now. Austin will mostly be focused on shipping 7.10 and keeping the normal review/patch/triaging cycles going until it's done. We're on track to fix all the major bugs we've assigned (see milestone:7.10.1).

Since my last post, we've also had other random assorted chatter on the mailing lists by the dev team:

  • In light of a recent large bug in GHC which can be used to derive unsafeCoerce, GHC HQ has decided to push back the 7.10 release a bit longer to about March, in order to fix this bug and ferret out the little fallout afterwords. It turns out this isn't a simple bug to fix, but luckily a fix is being worked on already.
  • David Feuer has a question: why is undefined so special? In particular, it seems as if undefined can be specially used as a value with a type of kind # as well as *. It turns out GHC has a special notion of subkinding, and undefined has a type more special than meets the eye which allows this, as Adam Gundry replied.
  • Greg Weber opened up a discussion about 'Restricted Template Haskell', which would hopefully make it easier for users to see what a TH computation is actually doing. It turns out - as noted by Simon - that Typed Template Haskell is perhaps closer to what Greg wants. The proposal and discussion then resulted in us realising that the typed TH documentation is rather poor! Hopefully Greg or someone can swing in to improve things.

Closed tickets the past two weeks include: #10028, #10040, #10031, #9935, #9928, #2615, #10048, #10057, #10054, #10060, #10017, #10038, #9937, #8796, #10030, #9988, #10066, #7425, #7424, #7434, #10041, #2917, #4834, #10004, #10050, #10020, #10036, #9213, and #10047.

GHC 7.10 Prelude: we need your opinion

This post asks for your help in deciding how to proceed with some Prelude changes in GHC 7.10. Please read on, but all the info is also at the survey link, here: Deadline is 21 Feb 2015.

The Core Libraries Committee (CLC) is responsible for developing the core libraries that ship with GHC. This is an important but painstaking task, and we owe the CLC a big vote of thanks for taking it on.

For over a year the CLC has been working on integrating the Foldable and Traversable classes (shipped in base in GHC 7.8) into the core libraries, and into the Prelude in particular. Detailed planning for GHC 7.10 started in the autumn of 2014, and the CLC went ahead with this integration.

Then we had a failure of communication. As these changes affect the Prelude, which is in scope for all users of Haskell, these changes should be held to a higher bar than the regular libraries@ review process. However, the Foldable/Traversable changes were not particularly well signposted. Many people have only recently woken up to them, and some have objected (both in principle and detail).

This is an extremely unfortunate situation. On the one hand we are at RC2 for GHC 7.10, so library authors have invested effort in updating their libraries to the new Prelude. On the other, altering the Prelude is in effect altering the language, something we take pretty seriously. We should have had this debate back in 2014, but here we are, and it is unproductive to argue about whose fault it is. We all share responsibility. We need to decide what to do now. A small group of us met by Skype and we've decided to do this:

  • Push back GHC 7.10's release by at least a month, to late March. This delay also gives us breathing space to address an unrelated show-stopping bug, Trac #9858.
  • Invite input from the Haskell community on which of two approaches to adopt (this survey). The main questions revolve around impact on the Haskell ecosystem (commercial applications, teaching, libraries, etc etc), so we want to ask your opinion rather than guess it.
  • Ask Simon Marlow and Simon Peyton Jones to decide which approach to follow for GHC 7.10.

Wiki pages have been created summarizing these two primary alternatives, including many more points and counter-points and technical details:

This survey invites your input on which plan we should follow. Would you please

  • Read the details of the alternative plans on the three wiki pages above
  • Add your response to the survey

Please do read the background. Well-informed responses will help. Thank you!

DEADLINE: 21 February 2015

Simon PJ