[Haskell-beginners] How to install new GHC ?

Michael Snoyman michael at snoyman.com
Tue Dec 12 13:54:38 UTC 2017


Hi Paul,

A Stackage snapshot specifies both a GHC version and a set of packages.
Stackage snapshots are built and tested to ensure that the packages are
compatible. While you could tell Stack to use a different GHC version with
a snapshot[1], this is unlikely to work, since GHC major releases usually
break some packages.

I think everyone who's trying to help you (both with Cabal and Stack
workflows) would be able to do so better if you explain which package
you're trying to use which is no longer available in Stackage Nightly. In
some cases, you can simply add it as an extra dependencies for Stack (e.g.,
`extra-deps: [acme-missiles-0.3]`), while in others there is some inherent
incompatibility.

Right now, you'll just be getting guesses about how to theoretically get
some unknown package to build with a bunch of others.

Michael

[1] Using a setting like `compiler: ghc-8.2.2`

On Tue, Dec 12, 2017 at 3:43 PM, Baa <aquagnu at gmail.com> wrote:

> @David: I tried to switch to nightly but in project's .yaml file and
> got error about missing of some library (as I understand, it is missing
> in last nightly). So, if I try to do it through .yaml file then how to
> use new GHC (8.2.2) but with LTS for 8.0.2? Is it possible? I need last
> stable LTS where all libraries (using in the projects) exist, but with
> new GHC 8.2.2 which is too new for stable LTS. As I read somewhere, GHC
> version and Stackage version are linked together hardly in stack tool,
> or?
>
> > You can see how to configure stack here:
> > https://github.com/commercialhaskell/stack/blob/release/doc/yaml_
> configuration.md
> >
> > The short of it is that to have stack ghci choose a particular
> > version of ghc, you probably need to modify
> > ~/.stack/global/stack.yaml, change resolver to something here
> > https://www.stackage.org/snapshots that has your version of ghc and
> > dependencies similar to what your project wants.  For example
> > 'nightly-2017-12-10'.
> >
> > On Tue, Dec 12, 2017 at 7:53 AM, Baa <aquagnu at gmail.com> wrote:
> >
> > > @Francesco: unfortunately nightly misses some package. So, I tried:
> > >
> > >   $ stack --resolver=ghc-8.2.2 setup --reinstall
> > >   Preparing to install GHC (tinfo6) to an isolated location. This
> > > will not interfere with any system-level installation. Already
> > > downloaded. Installed GHC.
> > >
> > >   stack will use a sandboxed GHC it installed
> > >   For more information on paths, see 'stack path' and 'stack exec
> > > env' To use this GHC and packages outside of a project, consider
> > > using: stack ghc, stack ghci, stack runghc, or stack exec
> > >
> > > So seems that 8.2.2 was installed, right? But how to build the
> > > project with new GHC now? I never used cabal before, `stack ghci`
> > > still runs 8.0.2 instead of 8.2.2. Installed GHC 8.2.2 does not
> > > correspond to .yaml file LTS - maybe this is a reason why old 8.0.2
> > > is stil used...
> > >
> > > When I try cabal build/new-build/repl I get:
> > >
> > >   cabal: The program 'ghc' version >=6.4 is required but it could
> > > not be found.
> > >
> > > So, cabal does not know about installed GHC versions (at least
> > > 8.0.2, used by stack). I tried --require-sandbox but without
> > > success.
> > >
> > >
> > > > On Tue, Dec 12, 2017 at 01:56:03PM +0200, Baa wrote:
> > > > > Would somebody explain me what is wrong here and how I can test
> > > > > a project with new 8.2.2 GHC?
> > > >
> > > > Hello Paul, I don't think stack lts has 8.2.2 just yet. Use a
> > > > nightly or download/install ghc from here and compile your project
> > > > with the new `cabal new-build`.
> > > >
> > > > [1] https://www.haskell.org/ghc/download_ghc_8_2_2.html#binaries
> > > >
> > > >
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> > >
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