Re: [GHC] #710: library reorganisation

#710: library reorganisation
-----------------------------+----------------------------------------------
  Reporter:  simonmar        |          Owner:          
      Type:  task            |         Status:  new     
  Priority:  normal          |      Milestone:  6.8     
 Component:  libraries/base  |        Version:  6.4.1   
  Severity:  normal          |     Resolution:          
  Keywords:                  |             Os:  Multiple
Difficulty:  Unknown         |   Architecture:  Multiple
-----------------------------+----------------------------------------------
Changes (by igloo):

  * architecture:  Unknown => Multiple
  * milestone:  => 6.8
  * os:  Unknown => Multiple

Comment:

 I spent some time looking at this. There are a number of issues that need
 to be resolved, or at least it would be better if they could be resolved
 first:
  * Problem using `--make` when compiling the base package ([ticket:
 #909]).
  * We'd lose the ability to do parallel module building within each
 library ([ticket: #910]).
  * Currently the implementations don't agree on what `Read` is, as the new
 `ReadP` requires rank-2 or rank-n polymorphism. I am told Haskell' will
 have one or the other, so this will come in time.
  * The code used by default class definitions needs to be pretty low down
 in the hierarchy, and in particular `fail s = error s` in the `Monad`
 class pulls in the huge exception type. This might be simplified with an
 extensible exception replacement?
  * For the deps from common packages to impl-specific packages we
 obviously need some sort of conditional support in Cabal.
  * Standalone deriving declarations (separate from the data declaration)
 make some things a lot easier. I think bringert has a working
 implementation for GHC, but it only truly helps if it's in all impls;
 something for Haskell'?
  * It's unfortunate that we can't make imported and exported class
 instances explicit, so the compiler won't be checking that we are giving
 consistency across impls.

 In what follows, I haven't given a huge amount of thought to names, but I
 don't think there's any need to do so yet.

 My conclusions were that ultimately something like this would be good
 (with <impl> replaced with ghc, hugs, ...):
  * `<impl>-prim` at the bottom; defines things like the `Int` type
 (basically all the types and functions needed by the next layer.
  * `base-types-classes` next, which just have class declarations but
 probably no instances.
  * `<impl>-base next`; This is where all GHC's instances with `I#`'s etc
 would go.
  * `base` on top of that, with anything that can't be forked off into
 another package.
 I also managed to fork off
  * `array`
  * `containers` (`Data.{FunctorM, Foldable, Graph, IntMap, IntSet, Map,
 Set, Queue, Sequence, Tree, Traversable`)
  * `bytestring`
  * `printf`
 and it also looked plausible that `io` and/or `concurrency` would also be
 able to be pulled out, but by that point I had run into enough of the
 issues above that I stopped working on it. The rest can be looked at in
 more detail when we come to do this for real.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/710>
GHC <http://www.haskell.org/ghc/>
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