- ghc-devs - Haskell.org

seq#: do we actually need it as a primitive?
by David Feuer 11 Jan '15

11 Jan '15

I've read about the inlining issues surrounding Control.Exception.evaluate that seem to have prompted the creation of seq#, but I'm still missing something. Isn't seq# a s the same as let !a' = a in (# s, a' #) ? David

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RE: Redundant constraints
by Simon Peyton Jones 10 Jan '15

10 Jan '15

| Current master of containers has no more unnecessary constraints, | although I had to use the | where _ = ... | trick | | Do you want me to release a bugfix version of containers? I'll let Austin decide. I _think_ that all we need do is update the GHC repo to point to your new commit in 'containers'; we don't need an actual release. Over to you, Austin Simon | -----Original Message----- | From: Milan Straka [mailto:fox@ucw.cz] | Sent: 10 January 2015 13:45 | To: Simon Peyton Jones | Cc: ghc-devs(a)haskell.org; Johan Tibell | Subject: Re: Redundant constraints | | Hi Simon and all, | | > -----Original message----- | > From: Simon Peyton Jones <simonpj(a)microsoft.com> | > Sent: 7 Jan 2015, 15:19 | > | > Friends | > I've pushed a big patch that adds -fwarn-redundant-constraints (on by | default). It tells you when a constraint in a signature is unnecessary, | e.g. | > f :: Ord a => a -> a -> Bool | > f x y = True | > I think I have done all the necessary library updates etc, so | everything should build fine. | > Four libraries which we don't maintain have such warnings (MANY of them | in transformers) so I'm ccing the maintainers: | > | > o containers | | thanks, a neat feature :) | | Current master of containers has no more unnecessary constraints, | although I had to use the | where _ = ... | trick once -- we have two versions of Data.Sequence.fromArray function, | and the GHC version did not need the (Ix *) constraint, but the standard | Haskell version does. | | Do you want me to release a bugfix version of containers? | | Cheers, | Milan

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Possible unpackFS problem
by Alan & Kim Zimmerman 10 Jan '15

10 Jan '15

While doing further round-trip testing, I cam across the following issue Original source module Deprecation {-# Deprecated ["This is a module \"deprecation\"", "multi-line"] #-} ( foo ) where Pretty-printed AST via ppr (L {examples/Deprecation.hs:(3,1)-(4,30)} (DeprecatedTxt (L {examples/Deprecation.hs:3:1-14} "{-# Deprecated") [ (L {examples/Deprecation.hs:3:17-50} {FastString: "This is a module \"deprecation\""}), (L {examples/Deprecation.hs:4:14-25} {FastString: "multi-line"})]))) output where the FastString is converted to a string via unpackFS module Deprecation {-# Deprecated ["This is a module "deprecation"", "multi-line"] #-} ( foo ) where So, the ppr (via Pretty.ftext) is able to reproduce the escape characters in original string, but unpackFS does not. Is this a problem for anyone else? Regards Aan

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How to get notifications when a build fails?
by Eric Seidel 10 Jan '15

10 Jan '15

Hi devs, Is there any way to make Phab email you when a revision you've submitted fails to build? I looked through the settings but couldn't find anything that seems to fit the bill. Thanks! Eric

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Milestones
by David Feuer 09 Jan '15

09 Jan '15

I took the liberty of pushing back the milestones for a few tickets that looked unlikely to be acted on for 7.10.1, based on a combination of severity, recent activity, and perceived intrusiveness. If anyone objects, please move them back. #9314: Each object file in a static archive file (.a) is loaded into its own mmap()ed page #8440: Get rid of the remaining static flags #8634: Relax functional dependency coherence check ("liberal coverage condition") David

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pef T3294
by Simon Peyton Jones 09 Jan '15

09 Jan '15

perf/compiler T3294 [stat not good enough] (normal) This test is failing on Phab all the time now. but it doesn't fail on my machine, so I can't see what's wrong. Could someone look? Simion

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Shipping core libraries with debug symbols
by Johan Tibell 09 Jan '15

09 Jan '15

Hi! We are now able to generate DWARF debug info, by passing -g to GHC. This will allow for better debugging (e.g. using GDB) and profiling (e.g. using Linux perf events). To make this feature more user accessible we need to ship debug info for the core libraries (and perhaps the RTS). The reason we need to ship debug info is that it's difficult, or impossible in the case of base, for the user to rebuild these libraries.The question is, how do we do this well? I don't think our "way" solution works very well. It causes us to recompile too much and GHC doesn't know which "ways" have been built or not. I believe other compilers, e.g. GCC, ship debug symbols in separate files ( https://packages.debian.org/sid/libc-dbg) that e.g. GDB can then look up. -- Johan

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Deprecating functions
by Jan Stolarek 09 Jan '15

09 Jan '15

I want to deprecate some Template Haskell functions in GHC 7.12 and then remove them in GHC 7.14 (or whatever version that comes after 7.12). Do we have any workflow for remembering these kind of things? I was thinking about adding a conditional error: #if __GLASGOW_HASKELL__ > 712 #error Remove functions foo bar from TH #endif Is this a good way of doing this? Or should I do it differently? Janek

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warn-redundant-constraints present as errors
by Alan & Kim Zimmerman 09 Jan '15

09 Jan '15

This is a great feature, here is some feedback My syntax highlighter in emacs expects warnings to have the word "warning" in them. So for the two warnings reported below, the first is highlighted as an error, and the second as a warning Language/Haskell/Refact/Utils/TypeUtils.hs:3036:17: Redundant constraint: SYB.Data t In the type signature for: duplicateDecl :: SYB.Data t => [GHC.LHsBind GHC.Name] -> t -> GHC.Name -> GHC.Name -> RefactGhc [GHC.LHsBind GHC.Name] Language/Haskell/Refact/Utils/TypeUtils.hs:3045:7: Warning: Defined but not used: ‘toks This is in a ghci session, and the file loads without problems, so it is indeed a warning. Can we perhaps add the word "Warning" to the output for Redundant constraints? I also had a situation where it asked me to remove a whole lot of constraints from different functions, I did them in batches, so did not remove them all from the file at once, and at some point I had to add at least one of them back, albeit based on an error message. Regards Alan

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Redundant constraints
by Simon Peyton Jones 09 Jan '15

09 Jan '15

Friends I've pushed a big patch that adds -fwarn-redundant-constraints (on by default). It tells you when a constraint in a signature is unnecessary, e.g. f :: Ord a => a -> a -> Bool f x y = True I think I have done all the necessary library updates etc, so everything should build fine. Four libraries which we don't maintain have such warnings (MANY of them in transformers) so I'm ccing the maintainers: o containers o haskeline o transformers o binary Enjoy! Simon

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