[commit: ghc] master: Improve the equality-floating story (again), to fix Trac #8644 (9e10d18)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/9e10d1883d7ea5ea422cda79b426f51d2b59b14d/ghc

>---------------------------------------------------------------

commit 9e10d1883d7ea5ea422cda79b426f51d2b59b14d
Author: Simon Peyton Jones <simonpj at microsoft.com>
Date:   Fri Jan 3 16:04:04 2014 +0000

    Improve the equality-floating story (again), to fix Trac #8644
    
    We float equalities out of implications whose 'givens' include equalities.
    But it's a bit tricky knowing whether some givens do or do not include
    equalities, as #8644 shows.  There the given has type 'c' (which might
    have equalities), but we discover that 'c ~ ()', which definitely doesn't.
    
    In short, we must look at the givens *after* normalisation, not before.
    Moreover, something similar happens in approximateWC, where we need
    to ask whether an implication has given equalities.
    
    This patch does the job:
    
    * Add a Boolean field inert_no_eqs to InertCans, which records
      whether we've added a non-constant equality
    
    * Add a field ic_no_eqs to Implication, which records whether the
      ic_given binders include any equalities
    
    * Get rid of Inst.hasEqualities altogether
    
    On the way I did some un-forced refactoring
    
    * Introduce the auxiliary function TcCanonical.flattenNestedFamApp
    
    * Kill off FamHeadMap and PredMap in favour of
      the new FunEqMap and DictMap respectively


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9e10d1883d7ea5ea422cda79b426f51d2b59b14d
 compiler/typecheck/Inst.lhs        |   19 ---
 compiler/typecheck/TcCanonical.lhs |   81 +++++-----
 compiler/typecheck/TcInteract.lhs  |   51 ++++---
 compiler/typecheck/TcRnTypes.lhs   |   11 +-
 compiler/typecheck/TcRules.lhs     |    2 +
 compiler/typecheck/TcSMonad.lhs    |  292 ++++++++++++++++++------------------
 compiler/typecheck/TcSimplify.lhs  |   64 +++++---
 compiler/typecheck/TcUnify.lhs     |   15 +-
 8 files changed, 283 insertions(+), 252 deletions(-)

Diff suppressed because of size. To see it, use:

    git diff-tree --root --patch-with-stat --no-color --find-copies-harder --ignore-space-at-eol --cc 9e10d1883d7ea5ea422cda79b426f51d2b59b14d