diff options
| -rw-r--r-- | libraries/ghc-prim/GHC/Classes.hs | 38 |
1 files changed, 22 insertions, 16 deletions
diff --git a/libraries/ghc-prim/GHC/Classes.hs b/libraries/ghc-prim/GHC/Classes.hs index 11438838d9..14e7ae37b0 100644 --- a/libraries/ghc-prim/GHC/Classes.hs +++ b/libraries/ghc-prim/GHC/Classes.hs @@ -37,7 +37,7 @@ module GHC.Classes( Eq(..), Ord(..), -- ** Monomorphic equality operators - -- | See GHC.Classes#matching_overloaded_methods_in_rules + -- $matching_overloaded_methods_in_rules eqInt, neInt, eqWord, neWord, eqChar, neChar, @@ -81,9 +81,11 @@ Matching on class methods (e.g. @(==)@) in rewrite rules tends to be a bit fragile. For instance, consider this motivating example from the @bytestring@ library, -> break :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString) -> breakByte :: Word8 -> ByteString -> (ByteString, ByteString) -> {-# RULES "break -> breakByte" forall a. break (== x) = breakByte x #-} +@ +break :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString) +breakByte :: Word8 -> ByteString -> (ByteString, ByteString) +\{\-\# RULES "break -> breakByte" forall a. break (== x) = breakByte x \#\-\} +@ Here we have two functions, with @breakByte@ providing an optimized implementation of @break@ where the predicate is merely testing for equality @@ -95,23 +97,27 @@ For this reason, most of the primitive types in @base@ have 'Eq' and 'Ord' instances defined in terms of helper functions with inlinings delayed to phase 1. For instance, @Word8@\'s @Eq@ instance looks like, -> instance Eq Word8 where -> (==) = eqWord8 -> (/=) = neWord8 -> -> eqWord8, neWord8 :: Word8 -> Word8 -> Bool -> eqWord8 (W8# x) (W8# y) = ... -> neWord8 (W8# x) (W8# y) = ... -> {-# INLINE [1] eqWord8 #-} -> {-# INLINE [1] neWord8 #-} +@ +instance Eq Word8 where + (==) = eqWord8 + (/=) = neWord8 + +eqWord8, neWord8 :: Word8 -> Word8 -> Bool +eqWord8 (W8# x) (W8# y) = ... +neWord8 (W8# x) (W8# y) = ... +\{\-\# INLINE [1] eqWord8 \#\-\} +\{\-\# INLINE [1] neWord8 \#\-\} +@ This allows us to save our @break@ rule above by rewriting it to instead match against @eqWord8@, -> {-# RULES "break -> breakByte" forall a. break (`eqWord8` x) = breakByte x #-} +@ +\{\-\# RULES "break -> breakByte" forall a. break (`eqWord8` x) = breakByte x \#\-\} +@ -Currently this is only done for '(==)', '(/=)', '(<)', '(<=)', '(>)', and '(>=)' -for the types in "GHC.Word" and "GHC.Int". +Currently this is only done for @('==')@, @('/=')@, @('<')@, @('<=')@, @('>')@, +and @('>=')@ for the types in "GHC.Word" and "GHC.Int". -} -- | The 'Eq' class defines equality ('==') and inequality ('/='). |