[commit: ghc] master: Rearrange the typechecking of arrows, especially arrow "forms" (c3ad38d)

[Simon Peyton Jones]

Repository : http://darcs.haskell.org/ghc.git/

On branch  : master

http://hackage.haskell.org/trac/ghc/changeset/c3ad38d7dc39ef583ddfb586413baa2e57ca3ee8

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

commit c3ad38d7dc39ef583ddfb586413baa2e57ca3ee8
Author: Simon Peyton Jones <simonpj at microsoft.com>
Date:   Mon Mar 4 09:40:56 2013 +0000

    Rearrange the typechecking of arrows, especially arrow "forms"
    
    The typechecking of arrow forms (in GHC 7.6) is known to be bogus, as
    described in Trac #5609, because it marches down tuple types that may
    not yet be fully worked out, depending on when constraint solving
    happens.  Moreover, coercions are generated and simply discarded.  The
    fact that it works at all is a miracle.
    
    This refactoring is based on a conversation with Ross, where we
    rearranged the typing of the argument stack, so that the arrows
    have the form
       a (env, (arg1, (arg2, ...(argn, ())))) res
    rather than
       a (arg1, (arg2, ...(argn, env))) res
    as it was before.
    
    This is vastly simpler to typecheck; just look at the beautiful,
    simple type checking of arrow forms now!
    
    We need a new HsCmdCast to capture the coercions generated from
    the argument stack.
    
    This leaves us in a better position to tackle the open arrow tickets
     * Trac #5777 still fails.  (I was hoping this patch would cure it.)
     * Trac #5609 is too complicated for me to grok.  Ross?
     * Trac #344
     * Trac #5333

 compiler/deSugar/Coverage.lhs     |   3 +
 compiler/deSugar/DsArrows.lhs     | 484 +++++++++++++++++++++-----------------
 compiler/hsSyn/HsExpr.lhs         |  13 +-
 compiler/hsSyn/HsUtils.lhs        |   7 +-
 compiler/parser/Parser.y.pp       |   4 +-
 compiler/parser/RdrHsSyn.lhs      |   4 +-
 compiler/rename/RnExpr.lhs        |   4 +-
 compiler/rename/RnTypes.lhs       |   2 +-
 compiler/typecheck/TcArrows.lhs   | 272 ++++++++++-----------
 compiler/typecheck/TcHsSyn.lhs    |   6 +-
 docs/users_guide/glasgow_exts.xml |  48 ++--
 11 files changed, 460 insertions(+), 387 deletions(-)


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

    git show c3ad38d7dc39ef583ddfb586413baa2e57ca3ee8