Improving the "Get Haskell Experience"

[Mark Lentczner]

*tl;dr: We'd like to incorporate stack into Haskell Platform, and stop
shipping pre-built packages, so we banish cabal hell, and have a single
common way to 'get Haskell' that just works.*

At ICFP '14, there were several long group discussions of the state of
"getting Haskell", including Haskell Platform, Stackage, and other
approaches. Over the last year, there have been a few more public
discussions and evolution on the ideas, and other installer developments.
In particular, Stackage's LTS package sets are a direct development from
this work, and the release of stack has offered new options.

Today, drawing from all this good work and ideas from so many, we'd would
like to propose a concrete plan:

   - Haskell Platform becomes the standard way to get *GHC* and related
   tools: *alex*, *cabal*, *happy*, *hscolour*, and *stack*. It's a
   user-friendly, cross-platform installer that gives a standard way to "get
   Haskell" for most users.
   - Use the *stack* model for package installation:
   - The global db has only the GHC packages
      - There is a package db for each curated set, Haskell Platform
      becomes one such set
      - Projects each have their own package db, much like sandboxes.
   - Haskell Platform's installer will no longer include pre-built,
   pre-installed packages other than GHC's set. Instead, it is configured so
   that *stack* can be used to build and install, on as needed, the
   corresponding Haskell Platform release packages.

We think this plan solves many different community needs:

   - We have a clear way to "get Haskell" that works for a wide variety of
   use cases.
   - HP installer gets much smaller, and about as minimal as a working
   installation can get.
   - By leaving most packages out of the global database, users of
   cabal-install, will now have far fewer problems. Sandbox builds should now
   never give users "cabal hell" like warnings.
   - By building and installing the Platform packages into it's own package
   db, users get the benefit of building and installing these common packages
   only once per system, yet can easily bypass them for any given project if
   desired.
   - Since the Platform packages are now built and installed as needed,
   installing on smaller systems or servers without OpenGL will work.

To do this, we have a bit of work ahead of us: We need to settle on
installation layout for each OS (including getting msys into the Windows
installer); decide on the naming and versioning of the Platform package set
(is it just LTS? does it have a different life cycle? etc...); getting
*stack* ready such a distribution; and configuring (or updating)
*cabal-install* to support the three-layer package db scheme. We think we
can do this in short order.

We recognize this represents a significant change for the Platform, and
will require buy-in from the various parts, especially *ghc*, *cabal*, and
*stack*. We'd like to get your input.

- Michael & Mark
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