[commit: ghc] wip/pattern-synonym-backport: In pattern synonym matchers, support unboxed continuation results (fixes #9783). (a91a2af)

[git at git.haskell.org]

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

On branch  : wip/pattern-synonym-backport
Link       : http://ghc.haskell.org/trac/ghc/changeset/a91a2afa3a7e06f2f78ec4d479cc7ed527d305c5/ghc

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commit a91a2afa3a7e06f2f78ec4d479cc7ed527d305c5
Author: Dr. ERDI Gergo <gergo at erdi.hu>
Date:   Sat Dec 20 10:51:09 2014 +0800

    In pattern synonym matchers, support unboxed continuation results (fixes #9783).
    
    This requires ensuring the continuations have arguments by adding a dummy
    Void# argument when needed. This is so that matching on a pattern synonym
    is lazy even when the result is unboxed, e.g.
    
        pattern P = ()
        f P = 0#
    
    In this case, without dummy arguments, the generated matcher's type would be
    
       $mP :: forall (r :: ?). () -> r -> r -> r
    
    which is called in `f` at type `() -> Int# -> Int# -> Int#`,
    so it would be strict, in particular, in the failure continuation
    of `patError`.
    
    We work around this by making sure both continuations have arguments:
    
      $mP :: forall (r :: ?). () -> (Void# -> r) -> (Void# -> r) -> r
    
    Of course, if `P` (and thus, the success continuation) has any arguments,
    we are only adding the extra dummy argument to the failure continuation.
    
    (cherry picked from commit 474e535b6b121809a8d75df5a4c37dc574d3d302)


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a91a2afa3a7e06f2f78ec4d479cc7ed527d305c5
 compiler/basicTypes/PatSyn.lhs                     | 29 ++++++++++++++------
 compiler/deSugar/DsUtils.lhs                       |  7 ++++-
 compiler/typecheck/TcPatSyn.lhs                    | 31 +++++++++++-----------
 testsuite/tests/patsyn/should_run/.gitignore       |  1 +
 testsuite/tests/patsyn/should_run/T9783.hs         | 15 +++++++++++
 .../should_run/T9783.stdout}                       |  2 +-
 testsuite/tests/patsyn/should_run/all.T            |  1 +
 7 files changed, 61 insertions(+), 25 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 a91a2afa3a7e06f2f78ec4d479cc7ed527d305c5