[skip ci] Fix 'Ord' documentation inconsistency

Current documentation for the `Ord` typeclass is inconsistent. It
simultaneously mentions that:

> The 'Ord' class is used for totally ordered datatypes.

And:

> The Haskell Report defines no laws for 'Ord'. However, '<=' is
> customarily expected to implement a non-strict partial order […]

The Haskell report (both 98 and 2010 versions) mentions total ordering,
which implicitly does define laws. Moreover, `compare :: Ord a => a -> a
-> Ordering` and `data Ordering = LT | EQ | GT` imply that the order is
indeed total (there is no way to say that two elements are not
comparable). This MR fixes the Haddock comment, and adds a comparability
law to the list of suggested properties.

1 files changed, 4 insertions, 4 deletions

diff --git a/libraries/ghc-prim/GHC/Classes.hs b/libraries/ghc-prim/GHC/Classes.hs
index 70749097dd..83ba27a767 100644
--- a/libraries/ghc-prim/GHC/Classes.hs
+++ b/libraries/ghc-prim/GHC/Classes.hs
@@ -307,15 +307,15 @@ instance Ord TyCon where
 -- 'Ordering' datatype allows a single comparison to determine the precise
 -- ordering of two objects.
 --
--- The Haskell Report defines no laws for 'Ord'. However, '<=' is customarily
--- expected to implement a non-strict partial order and have the following
--- properties:
+-- 'Ord', as defined by the Haskell report, implements a total order and has the
+-- following properties:
 --
+-- [__Comparability__]: @x <= y || y <= x@ = 'True'
 -- [__Transitivity__]: if @x <= y && y <= z@ = 'True', then @x <= z@ = 'True'
 -- [__Reflexivity__]: @x <= x@ = 'True'
 -- [__Antisymmetry__]: if @x <= y && y <= x@ = 'True', then @x == y@ = 'True'
 --
--- Note that the following operator interactions are expected to hold:
+-- The following operator interactions are expected to hold:
 --
 -- 1. @x >= y@ = @y <= x@
 -- 2. @x < y@ = @x <= y && x /= y@