Right now, Hackage has no concept of a stable and an unstable
release of a package. As a result, authors are hesitant to release
code to Hackage unless it's already stable. But it's difficult to
get people to test new versions of packages if it's difficult to
install. Installing a single new package from Github may not be
difficult, but sometimes you want people to test out a new set of
versions for multiple packages, which can be tedious. This blog
post will demonstrate how you can use Stackage Server to make that
While the primary purpose of Stackage Server is to host the
official Stackage snapshots, it has been designed as completely
generic server for hosting any set of packages desired, including
custom packages not yet released to Hackage. All you need to do
- Create an account on Stackage Server (by logging in with Google+ or
- Create a tarball in the correct format (described below)
- Upload it from the snapshot upload page
You can download a sample bundle file by clicking on the "Bundle" link at the
top of any snapshot page. It might be useful to open one up as you looking
through the rest of this section.
You can view the tarball parsing code in the Stackage Server codebase
itself. The format is designed to be simple to replicate and
extensible for future functionality. (In fact, the slug file
feature I mention below was only recently
The tarball must be
tarred in a format that
the tar package
can read, and then gzipped. Each file in the tarball is treated
indepedently. Directory structure inside the tarball is ignored.
tar cfz mybundle.tar.gz somedirectory is usually
sufficient to meet these criterion.
Each file inside the tarball is treated separately. There are
four kinds of files recognized:
desc gives the human-readable title and
description for the snapshot. Put the title on the first line, and
the description on the following lines. (Note that, currently, we
only display the title on the site, though we may add the
description to the display in the future.)
slug is a recommendation for the short name of the
snapshot. For example, the most recent
GHC 7.8 snapshot as I write this is
which has a slug of
2014-11-26-ghc78-exc. Slugs must
be globally unique, so if someone else has already taken that slug,
Stackage Server will append a randomized token to the end.
hackage is a list of all the package/version combos
to be included in this snapshot from Hackage. For example, you
You're free to have multiple versions per package.
- Any file ending in
.tar.gz will be treated as a
custom sdist tarball, and will be made available for
download from stackage.org. This is how you can provide custom
versions of a package not released on Hackage. As an example of
this, here's a
snapshot with two unreleased packages in it (link removed).
Another use case is customizing an official Stackage snapshot.
For example, you may be using a certain snapshot, but want to get a
newer version of one of the packages from Hackage, or write a
custom patch for one of the package versions and use that. If so,
all you need to do is:
- Download the bundle file
- Tweak its contents
- Upload it
- Use the new URL
Replace or augment
The instructions for using a Stackage snapshot mention replacing
the hackage.haskell.org remote-repo line in your cabal config file
with the stackage.org URL. This makes sense if you're providing a
snapshot that has all the packages from Hackage that you'll need.
However, if you're testing out a few new packages, it's simpler to
just provide those few extra packages, and add an extra
remote-repo line to your config file instead of replacing the
primary entry. Note that this trick can be used to augment a
Stackage snapshot in addition to adding extra packages to
You should keep two things in mind when using Stackage Server in
- Snapshots you create live forever. In cases of extreme issues
(like accidentally uploading copyrighted data) we will of course
assist in removing the snapshot. But generally speaking, a snapshot
is forever, just like uploading a package to Hackage makes it
- All snapshots are publicly listed, so you
don't want to put any sensitive information in there. Of course,
the Stackage Server codebase is open source, so you're free to run
your own, private instance if you'd like. Alternatively, FP
Complete provides private Stackage Server instances as a service,
feel free to contact us for more
Creating a generic tool like that has the advantage that it can
be (ab)used to purposes other than the original intent of the
author. In this case, I've described some intended alternate use
cases for this functionality. If people come up with other
unintended use cases, let me know!
Subscribe to our blog via email
Email subscriptions come from our Atom feed and are handled by Blogtrottr. You will only receive notifications of blog posts, and can unsubscribe any time.
Do you like this blog post and need help with DevOps, Rust or functional programming? Contact us.