[commit: ghc] master: Replace (State# RealWorld) with Void# where we just want a 0-bit value (f438464)

[git at git.haskell.org]

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

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/f438464754ad9abd885acf3529606ca57945edc2/ghc

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

commit f438464754ad9abd885acf3529606ca57945edc2
Author: Simon Peyton Jones <simonpj at microsoft.com>
Date:   Fri Nov 22 15:23:22 2013 +0000

    Replace (State# RealWorld) with Void# where we just want a 0-bit value
    
    We were re-using the super-magical "state token" type (which has
    VoidRep and is zero bits wide) for situations in which we simply want
    to lambda-abstract over a zero-bit argument. For example, join points:
    
       case (case x of { True -> e1; False -> e2 }) of
          Red  -> f1
          Blue -> True
    
    ==>
    
      let $j1 = \voidArg::Void# -> f1
      in
      case x of
        True -> case e1 of
                  Red -> $j1 void
                  Blue -> True
        False -> case e2 of
                  Red -> $j1 void
                  Blue -> True
    
    This patch introduces
    
       * The new primitive type GHC.Prim.Void#, with PrimRep = VoidRep
    
       * A new global Id GHC.Prim.voidPrimId :: Void#.
         This has no binding because the code generator drops it,
         but is used as an argument (eg in the call of $j1)
    
       * A new local Id, MkId.voidArgId, which can be lambda-bound
         when you need to lambda-abstract over it.
    
    and uses them throughout.
    
    Now the State# thing is used only when we need state!


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

f438464754ad9abd885acf3529606ca57945edc2
 compiler/basicTypes/MkId.lhs       |   37 +++++++++++++++++++++---------------
 compiler/deSugar/DsUtils.lhs       |    9 +++++----
 compiler/prelude/PrelNames.lhs     |    6 ++++--
 compiler/prelude/TysPrim.lhs       |   11 ++++++++++-
 compiler/simplCore/Simplify.lhs    |    8 ++++----
 compiler/specialise/Specialise.lhs |    4 ++--
 compiler/stranal/WwLib.lhs         |   10 +++++-----
 compiler/types/Type.lhs            |   12 +++++++++---
 8 files changed, 61 insertions(+), 36 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 f438464754ad9abd885acf3529606ca57945edc2