[commit: ghc] master: A nice tidy-up for CvSubst and liftCoSubst (525aca2)

[Simon Peyton Jones]

Repository : ssh://darcs.haskell.org//srv/darcs/ghc

On branch  : master

http://hackage.haskell.org/trac/ghc/changeset/525aca2c11c510ce83a593b6cedfacc54a2b7806

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

commit 525aca2c11c510ce83a593b6cedfacc54a2b7806
Author: Simon Peyton Jones <simonpj at microsoft.com>
Date:   Sat Jul 23 18:36:58 2011 +0100

    A nice tidy-up for CvSubst and liftCoSubst
    
    A "lifting substitition" takes a *type* to a *coercion*, using a
    substitution that takes a *type variable* to a *coercion*.  We were
    using a CvSubst for this purpose, which was an awkward exception: in
    every other use of CvSubst, type variables map only to types.
    
    Turned out that Coercion.liftCoSubst is quite a small function, so I
    rewrote it with a special substitution type Coercion.LiftCoSubst, just
    for that purpose.  In doing so I found that the function itself was
    bizarrely over-complicated ... a direct result of mis-using CvSubst.
    
    So this patch makes it all simpler, faster, and easier to understand.
    No bugs fixed though!

 compiler/basicTypes/Var.lhs     |    3 +-
 compiler/basicTypes/VarSet.lhs  |    5 +-
 compiler/coreSyn/CoreLint.lhs   |    2 +-
 compiler/coreSyn/CoreSubst.lhs  |   12 ++--
 compiler/coreSyn/CoreUnfold.lhs |    7 +-
 compiler/iface/IfaceType.lhs    |   11 ++-
 compiler/simplCore/SimplEnv.lhs |    6 +-
 compiler/types/Coercion.lhs     |  117 ++++++++++++++++----------------------
 compiler/types/Type.lhs         |    2 +-
 compiler/types/TypeRep.lhs      |    6 +-
 10 files changed, 77 insertions(+), 94 deletions(-)


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

    git show 525aca2c11c510ce83a593b6cedfacc54a2b7806