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Diffstat (limited to 'docs/users_guide/bugs.rst')
| -rw-r--r-- | docs/users_guide/bugs.rst | 12 |
1 files changed, 11 insertions, 1 deletions
diff --git a/docs/users_guide/bugs.rst b/docs/users_guide/bugs.rst index 5b710aa35d..5d303636f4 100644 --- a/docs/users_guide/bugs.rst +++ b/docs/users_guide/bugs.rst @@ -152,7 +152,7 @@ Numbers, basic types, and built-in classes ``Num`` superclasses The ``Num`` class does not have ``Show`` or ``Eq`` superclasses. - + You can make code that works with both Haskell98/Haskell2010 and GHC by: @@ -178,6 +178,16 @@ Numbers, basic types, and built-in classes - Always define the ``bit``, ``testBit`` and ``popCount`` methods in ``Bits`` instances. +``Read`` class methods + The ``Read`` class has two extra methods, ``readPrec`` and + ``readListPrec``, that are not found in the Haskell 2010 since they rely + on the ``ReadPrec`` data type, which requires the :ghc-flag:`-XRankNTypes` + extension. GHC also derives ``Read`` instances by implementing ``readPrec`` + instead of ``readsPrec``, and relies on a default implementation of + ``readsPrec`` that is defined in terms of ``readPrec``. GHC adds these two + extra methods simply because ``ReadPrec`` is more efficient than ``ReadS`` + (the type on which ``readsPrec`` is based). + Extra instances The following extra instances are defined: :: |