April 2016 - Glasgow-haskell-users

Magic classes for Overloaded Record Fields, overlaps, FunDeps
by AntC 15 May '16

15 May '16

There's an intriguing comment here wrt anonymous records: https://ghc.haskell.org/trac/ghc/wiki/Records/OverloadedRecordFields/ MagicClasses#Designextension:anonymousrecords (End of the section) "... this doesn't quite work, because the two instances overlap, but it is possible with a bit more trickery" I could well understand if everybody's forgotten what was the "trickery", because ORF has been so long in the pipeline, but could anyone explain? Reason for the q: I'm looking at anonymous records myself, including extending, shortening and joining anon records. And yes overlapping instances are everywhere. Using type families isn't being too ergonomic. And I notice ORF has used FunDeps. But for me, FunDeps in the HList style is also rather ugly. Is there some trickery I'm missing? Thanks AntC

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[ANNOUNCE] GHC 8.0.1 release candidate 4 available
by Ben Gamari 29 Apr '16

29 Apr '16

Hello Haskellers, The GHC team is happy to announce the availability of fourth release candidate of the Glasgow Haskell Compiler's 8.0.1 release. Source and binary distributions can be found at, http://downloads.haskell.org/~ghc/8.0.1-rc4/ This is the last of four candidates leading up to the 8.0.1 release, addressing nearly all of the known issues of the previous candidates. These include, * A type-checker panic triggered by use of Typeable on a kind-polymorphic type constructor (#11334) * A type-checker explosion where -XTypeInType would gobble up massive amounts of memory when used in a data instance (#11407) * A variety of other typechecker issues (#11811, #11797, #11813, #11814) * A build issue seen on OS X (#11828) * Template Haskell can now produce instances with OVERLAPP{ING,ABLE,ED} pragmas * Autoconf has improved version checks for libdw (#11820) * Typeable and hs-boot files now interact nicely (#11824) * The build system now checks for the broken Apple `nm` utility (#11823, #11744) * Various issues involving unexpected laziness resulting in exception handlers not being invoked (#11555) * GHC now fails more gracefully when used with an older cabal-install release (#11558) * TypeInType now has proper documentation in the users guide (#11614) * The story surrounding type `RuntimeRep`s (formerly known as `Levity`) is now far better developed, closing several doors to unsafe behavior that TypeInType previously opened (#11473, #11723) * A long-standing bug in the constant-folding rules for `mod` for the `Word` type has been resolved (#11702) * Various issues introduced by OverloadedRecordFields have been fixed (#11662, #11401) * A regression in the typechecker resulting in the rejection of code in the `free` and `microlens` packages has been fixed (#11608) * A bug in the LLVM code generator which caused some programs to emit unbuildable LLVM IR has been fixed (#11649) * A bug where pattern synonyms defined in terms of a pattern match on a record would be rejected if the fields weren't written in the same order as they were defined has been resolved (#11633) * A bug in the runtime system's treatment of weak references which could result in segmentation faults in some cases has been fixed (#11108) * a variety of optimizations improving compiler performance have been merged * and many others Mac OS X users should be aware that the recent XCode 7.3 release ships with a broken `nm` utility which breaks the GHC build (#11744, #11823). The build system will check for this condition and request that the tree is configured to use the `nm-classic` utility if found. OS X users running XCode 7.3 are encouraged to open a ticket with Apple so that this issue may be fixed in future XCode releases. If no major issues pop up we expect that this will be the last release candidate before the final release, which we hope to push out in the coming weeks. Thanks to everyone who has contributed code, testing, builds, and bug reports thusfar! Cheers and happy testing, - Ben

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[ANNOUNCE] GHC 8.0.1 release candidate 3 available
by Ben Gamari 23 Apr '16

23 Apr '16

Hello Haskellers, The GHC team is happy to announce the availability of third release candidate of the Glasgow Haskell Compiler's 8.0.1 release. Source and binary distributions can be found at, http://downloads.haskell.org/~ghc/8.0.1-rc3/ This is the third of what will be four candidates leading up to the 8.0.1 release. As there are a number of known issues with this candidate, we expect to produce the fourth and final release candidate shortly. While we considered not releasing this candidate at all and instead skipping to rc4, we decided that it would be helpful to make it available despite its issues to increase the likelihood of catching any remaining bugs. That being said, this candidate lacks the range of binary distributions which we usually offer, * We are unable to release Windows bindists due to a compatibility issue which we didn't catch until after preparing the source distribution. * Binaries targeting Redhat distributions are currently not available Regardless, users for whom a distribution is available are encouraged to try this candidate as it fixes dozens of issues present in release candidate two. These include, * A type-checker panic triggered by use of Typeable on a kind-polymorphic type constructor (#11334) * A type-checker explosion where -XTypeInType would gobble up massive amounts of memory when used in a data instance (#11407) * Various issues involving unexpected laziness resulting in exception handlers not being invoked (#11555) * GHC now fails more gracefully when used with an older cabal-install release (#11558) * TypeInType now has proper documentation in the users guide (#11614) * The story surrounding type `RuntimeRep`s (formerly known as `Levity`) is now far better developed, closing several doors to unsafe behavior that TypeInType previously opened (#11473, #11723) * A long-standing bug in the constant-folding rules for `mod` for the `Word` type has been resolved (#11702) * Various issues introduced by OverloadedRecordFields have been fixed (#11662, #11401) * A regression in the typechecker resulting in the rejection of code in the `free` and `microlens` packages has been fixed (#11608) * A bug in the LLVM code generator which caused some programs to emit unbuildable LLVM IR has been fixed (#11649) * A bug where pattern synonyms defined in terms of a pattern match on a record would be rejected if the fields weren't written in the same order as they were defined has been resolved (#11633) * A bug in the runtime system's treatment of weak references which could result in segmentation faults in some cases has been fixed (#11108) * a variety of optimizations improving compiler performance have been merged * and many others Mac OS X users should be aware that the recent XCode 7.3 release ships with a broken `nm` utility which breaks the GHC build (#11744, #11823). Unfortunately, this candidate does not notice this brokenness and odd behavior can result. OS X users running XCode 7.3 are encouraged to open a ticket with Apple and build GHC with the `--with-nm=nm-classic` configure option until a fix is available. As mentioned earlier, there are a number of known issues with this candidate which will be addressed in release candidate four. These issues include, * A number of typechecker bugs (#11811, #11797, #11813, #11814) * A build issue seen on OS X (#11828) * Template Haskell lacks the ability to produce instances with OVERLAPP{ING,ABLE,ED} pragmas * Autoconf has inadequate version checks for libdw (#11820) * Typeable and hs-boot files interact poorly (#11824) * The build system doesn't check for the broken Apple `nm` utility, leading to unpredictable results (#11823, #11744) We hope to have release candidate four available by the middle of next week. Thanks to everyone who has contributed code, testing, builds, and bug reports thusfar! Cheers, - Ben

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