[commit: base] master: Typeable overhaul (see #5275) (903c1af)

[Simon Marlow]

Repository : ssh://darcs.haskell.org//srv/darcs/packages/base

On branch  : master

http://hackage.haskell.org/trac/ghc/changeset/903c1afa3bdd205dc5473c0fca1065d598145311

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

commit 903c1afa3bdd205dc5473c0fca1065d598145311
Author: Simon Marlow <marlowsd at gmail.com>
Date:   Fri Jul 8 10:39:24 2011 +0100

    Typeable overhaul (see #5275)
    
    Instances of Typeable used to call mkTyCon:
    
      mkTyCon :: String -> TyCon
    
    which internally kept a table mapping Strings to Ints, so that each
    TyCon could be given a unique Int for fast comparison.  This meant the
    String has to be unique across all types in the program.  However,
    derived instances of typeable used the qualified original
    name (e.g. "GHC.Types.Int") which is not necessarily unique, is
    non-portable, and exposes implementation details.
    
    The String passed to mkTyCon is returned by
    
      tyConString :: TyCon -> String
    
    which let the user get at this non-portable representation (also the
    Show instance returns this String).
    
    Now we store three Strings in TyCon.  The internal representation is
    this:
    
    data TyCon = TyCon {
       tyConHash    :: {-# UNPACK #-} !Fingerprint,
       tyConPackage :: String,
       tyConModule  :: String,
       tyConName    :: String
     }
    
    (internal representations are now provided by Data.Typeable.Internal)
    
    The fields of TyCon are not exposed via the public API.  Together the
    three fields tyConPackage, tyConModule and tyConName uniquely identify
    a TyCon, and the Fingerprint is a hash of the concatenation of these
    three Strings (so no more internal cache to map strings to unique
    Ids). tyConString now returns the value of tyConName only, so is
    therefore portable (but the String returned does not uniquely
    identify the TyCon).
    
    I've measured the performance impact of this change, and performance
    seems to be uniformly better.  This should improve things for SYB in
    particular.  Also, the size of the code generated for deriving
    Typeable is less than half as much as before.
    
    == API changes ==
    
    === mkTyCon is DEPRECATED ==
    
    mkTyCon is used by some hand-written instances of Typeable.  It still
    works as before, but is deprecated in favour of...
    
    === Add mkTyCon3 ===
    
      mkTyCon3 :: String -> String -> String -> TyCon
    
    mkTyCon3 takes the package, module, and name of the TyCon respectively.
    Most users can just derive Typeable, there's no need to use mkTyCon3.
    
    In due course we can rename mkTyCon3 back to mkTyCon.
    
    === typeRepKey changed ===
    
    Previously we had
    
      typeRepKey :: TypeRep -> IO Int
    
    but since we don't assign unique Ints to TypeReps any more, this is
    difficult to implement.  Instead we provide an abstract key type which
    is an instance of Eq and Ord, and internally is implemented by the
    fingerprint:
    
      data TypeRepKey -- abstract, instance of Eq, Ord
      typeRepKey :: TypeRep -> IO TypeRepKey
    
    typeRepKey is still in the IO monad, because the Ord instance is
    implementation-defined.

 Data/Typeable.hs               |  178 ++++++++----------------------
 Data/Typeable.hs-boot          |    5 +-
 Data/Typeable/Internal.hs      |   59 ++++++++++
 Data/Typeable/Internal.hs-boot |   19 +++
 Foreign/C/Types.hs             |    2 +
 GHC/Exception.lhs              |    1 +
 GHC/Fingerprint.hs             |   97 ++++++++++++++++
 GHC/Fingerprint.hs-boot        |   12 ++
 GHC/Fingerprint/Type.hs        |   19 +++
 base.cabal                     |    6 +-
 cbits/md5.c                    |  238 ++++++++++++++++++++++++++++++++++++++++
 configure.ac                   |    3 +
 include/md5.h                  |   24 ++++
 13 files changed, 526 insertions(+), 137 deletions(-)


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

    git show 903c1afa3bdd205dc5473c0fca1065d598145311