Re: [ANNOUNCE] GHC 8.2.1 available

Thanks for the reply. I got cabal-install from https://github.com/haskell/cabal/ and assumed it was the latest version... but now that I look carefully I see it has a 2.0 branch. I compiled it and I don't get that confusing "parse error" any more. It looks like a nicer error message in general too (except still missing some spaces, specifically "After searching the rest of the dependency tree exhaustively, these were the goals I've had most trouble fulfilling: karya, ekgTrying configure anyway."), so that's probably thanks to the solver improvements in 2.0. Since it's apparently just a bug in older cabal-installs I guess I won't bother trying to find it. On Wed, Jul 26, 2017 at 7:01 PM, Wolfgang Jeltsch wrote:

Hi!

I ran into the same problem.

Apparently, we need cabal-install 2.0, which has not been released yet. A preliminary solution is to use the development version from the 2.0 branch. Binary packages can be found at

http://ppa.launchpad.net/hvr/ghc/ubuntu/pool/main/c/cabal-install-2.0/ ,

for example. It is possible to extract the cabal-install executable from these packages, so that it can be installed without using some Linux distribution package manager.

All the best, Wolfgang

Am Mittwoch, den 26.07.2017, 18:45 -0700 schrieb Evan Laforge:

...

This seems like a silly question, but how can we install cabal-install now? The latest hackage version 1.24.0.2 has Cabal (>=1.24.2 && <1.25), but it looks like ghc Cabal is now at 2.*.

I ran into this because if I get:

% cabal install --only-dependencies Resolving dependencies... cabal: internal error when reading package index: failed to parse .cabal fileThe package index or index cache is probably corrupt. Running cabal update might fix it.

It seems to be triggered by having 'ekg' in the deps list, since if I take it out then I get some other errors about packages not liking the new base, which is true. 'ekg' also doesn't like the new base, but "internal error" is not the clearest way to express that :)

It's frustrating that cabal-install still doesn't report the parse error, even though the parse function returns one. It just ignores the ParseFailed case. I was going to try fixing it and send a pull request when I ran into the Cabal 2.* problem.

On Wed, Jul 26, 2017 at 7:15 AM, Ben Gamari wrote:

...

Wolfgang Jeltsch writes:

...

Am Samstag, den 22.07.2017, 23:03 -0400 schrieb Ben Gamari:

...

In addition, there are a number of new features,

* A new, more type-safe type reflection mechanism

* The long-awaited Backpack module system

* Deriving strategies to disambiguate between GHC's various instance deriving mechanisms

* Unboxed sum types, for efficient unpacked representation of sum data types

* Compact regions, allowing better control over garbage collection in the presence of large heaps containing many long-lived objects.

* Colorful messages and caret diagnostics for more legible errors

A more thorough list of the changes in this release can be found in the release notes,

https://haskell.org/ghc/docs/8.2.1/docs/html/users_guide/8.2.1 -notes.html

It seems that the release notes mention the new type reflection mechanism und colorful messages only in the “Highlights” section, not in the “Full details” section, and that they do not mention the Backpack module system and unboxed sums at all.

Yes, indeed these were oversights. They are fixed in the ghc-8.2 branch and I will try to push newly generated documentation shortly.

Cheers,

- Ben

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