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| author | f-a <fa-ml@ariis.it> | 2020-10-01 15:06:07 -0400 |
|---|---|---|
| committer | Ben Gamari <ben@smart-cactus.org> | 2020-10-16 10:14:39 -0400 |
| commit | 07b0db86595890dfca6f624e554cdb8c9b86d0cc (patch) | |
| tree | c5bb8a25cc55fe0ed048e008414f13186a11e3f8 | |
| parent | 9a9679dbfc77c600e6c2a031ccab37d203a19cf9 (diff) | |
| download | haskell-07b0db86595890dfca6f624e554cdb8c9b86d0cc.tar.gz | |
Clarify Eq documentation #18713
| -rw-r--r-- | libraries/ghc-prim/GHC/Classes.hs | 13 |
1 files changed, 4 insertions, 9 deletions
diff --git a/libraries/ghc-prim/GHC/Classes.hs b/libraries/ghc-prim/GHC/Classes.hs index 105875b450..70749097dd 100644 --- a/libraries/ghc-prim/GHC/Classes.hs +++ b/libraries/ghc-prim/GHC/Classes.hs @@ -125,18 +125,13 @@ and @('>=')@ for the types in "GHC.Word" and "GHC.Int". -- and 'Eq' may be derived for any datatype whose constituents are also -- instances of 'Eq'. -- --- The Haskell Report defines no laws for 'Eq'. However, '==' is customarily --- expected to implement an equivalence relationship where two values comparing --- equal are indistinguishable by "public" functions, with a "public" function --- being one not allowing to see implementation details. For example, for a --- type representing non-normalised natural numbers modulo 100, a "public" --- function doesn't make the difference between 1 and 201. It is expected to --- have the following properties: +-- The Haskell Report defines no laws for 'Eq'. However, instances are +-- encouraged to follow these properties: -- -- [__Reflexivity__]: @x == x@ = 'True' -- [__Symmetry__]: @x == y@ = @y == x@ -- [__Transitivity__]: if @x == y && y == z@ = 'True', then @x == z@ = 'True' --- [__Substitutivity__]: if @x == y@ = 'True' and @f@ is a "public" function +-- [__Extensionality__]: if @x == y@ = 'True' and @f@ is a function -- whose return type is an instance of 'Eq', then @f x == f y@ = 'True' -- [__Negation__]: @x /= y@ = @not (x == y)@ -- @@ -234,7 +229,7 @@ eqChar, neChar :: Char -> Char -> Bool -- >>> 0/0 == (0/0 :: Float) -- False -- --- Also note that `Float`'s 'Eq' instance does not satisfy substitutivity: +-- Also note that `Float`'s 'Eq' instance does not satisfy extensionality: -- -- >>> 0 == (-0 :: Float) -- True |