[Haskell-beginners] How to install new GHC ?
Michael Snoyman
michael at snoyman.com
Tue Dec 12 15:46:44 UTC 2017
IMO, there are two different cases you need to care about:
1. If you're writing an application, keeping broad support for lots of
compiler and library versions isn't vital. You can dictate exactly which
versions of dependencies your application is compiled with. I use this for
web applications I write and command line tools (including Stack), for
example. In this case: pick an LTS snapshot, add extra-deps on demand if
absolutely necessary, and then when you see a strong need (like upstream
bug fixes), update your stack.yaml to a newer snapshot to get new GHC and
library versions.
2. If you're writing a library that you expect others to be using, keep as
broad a support base as possible. This is encouraged by things like the
complex Travis config in the Stack docs[1], which build with many different
LTS snapshots, as well as using many versions of GHC and cabal-install (to
cover the dep solver case). This allows consumers of your library to more
easily mix and match which versions of dependencies they want to put
together.
When there is an upstream breaking change, it's tempting to just drop
support for the old version, add a lower bound in your cabal file to say "I
no longer support the old version," and move on. But IMO a nicer solution
for your users is to introduce conditional compilation, e.g.:
#if MIN_VERSION_transformers(0, 5, 0)
-- use transformers 0.5 or later
#else
-- use transformers 0.4 or earlier
#endif
This definitely adds extra burden to you as a writer, but it helps others
significantly. This is also strong motivation to try to avoid breaking
backwards compatibility in your APIs, as every such breakage can cause a
cascade of downstream pain[2].
I hope that answers your questions, let me know if you want me to clarify
any points here.
[1]
https://github.com/commercialhaskell/stack/blob/master/doc/travis-complex.yml
[2] In case anyone's wondering: this has nothing to do with bounds in your
cabal file, I'm talking about actual code breakage
On Tue, Dec 12, 2017 at 5:25 PM, Baa <aquagnu at gmail.com> wrote:
> @Michael, so my newbie's questions:
>
> - how Haskellers proceed in this case? Rewrites Template Haskells code
> after every switch to new versions? Or it's not common practice to
> switch projects from one GHC version to another? What about LTS? Do
> you switch to new one often? Is there a practice to keep project on
> one LTS/GHC versions and never to update them (I mean common, good
> known, convenient practice in Haskell)? For example, no problem to
> use out-of-date libraries in C/C++, in embedded development, etc, but
> what about Haskell?
>
> IMHO it's better to update due to bug fixing, new features, but it's
> interesting common practice in Haskell projects.
>
> ===
> Best regards, Paul
>
> > That's right, the template-haskell API frequently changes between
> > major releases of GHC.
> >
> > On Tue, Dec 12, 2017, 4:35 PM Baa <aquagnu at gmail.com> wrote:
> >
> > > @Michael Snoyman:
> > >
> > > I returned back all .cabal-files and added compiler: ghc-8.2.2,
> > > `stack build`
> > > printed out this:
> > >
> > > ---cut---
> > > Error: While constructing the build plan, the following
> > > exceptions were encountered:
> > >
> > > In the dependencies for Cabal-1.24.2.0:
> > > process-1.6.1.0 from stack configuration does not match
> > > >=1.1.0.1 && <1.5 (latest matching version is 1.4.3.0)
> > > needed due to my-common-utils-0.2.0.0 -> Cabal-1.24.2.0
> > >
> > > In the dependencies for versions-3.1.1:
> > > base-4.10.1.0 from stack configuration does not match >=4.8
> > > && <4.10 (latest matching version is 4.9.1.0)
> > > needed due to my-common-utils-0.2.0.0 -> versions-3.1.1
> > >
> > > Some potential ways to resolve this:
> > >
> > > * Recommended action: try adding the following to your
> > > extra-deps in /home/pavel/prj/automation/revcompl-mon/stack.yaml:
> > >
> > > - base-4.9.1.0
> > > - process-1.4.3.0
> > >
> > > * Set 'allow-newer: true' to ignore all version constraints and
> > > build anyway.
> > >
> > > * You may also want to try using the 'stack solver' command.
> > >
> > > Plan construction failed.
> > > ---cut---
> > >
> > > After adding "allow-newer: true" build process starts, all looked
> > > fine until:
> > >
> > > .../SimpleTagging.hs:281:51: error:
> > > • Couldn't match type ‘Type’ with ‘DerivClause’
> > > Expected type: [DerivClause]
> > > Actual type: [Type]
> > > • In the sixth argument of ‘DataD’, namely ‘derivs'’
> > > In the expression: DataD [] ty' tyVars Nothing newCs
> > > derivs' In the first argument of ‘(++)’, namely
> > > ‘[DataD [] ty' tyVars Nothing newCs derivs']’
> > > |
> > > 281 | return $ [DataD [] ty' tyVars Nothing newCs
> > > derivs'] ++ showInst
> > > | ^^^^^^^
> > >
> > > which IMHO means that TemplateHaskell ("API") was changed from
> > > 8.0.2 to 8.2.2 because the same code is compiling with old GHC
> > > 8.0.2.
> > >
> > >
> > > > 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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