Does the wording of the report specify "totally ordered" as a law? I think
it would be good to make that explicit, laying out the axioms for what a
total order is—similar to the current documentation in Data.Ord but
explicitly as the laws for the class.
The relationship between Eq and Ord should be explicitly specified too, if
it isn't.
On Wed, Feb 6, 2019, 12:53 Herbert Valerio Riedel On Wed, Feb 6, 2019 at 9:43 PM chessai . Per GHC.Classes (haddock-viewable from Data.Ord) "The Haskell Report defines no laws for Ord. However, <= is
customarily expected to implement a non-strict partial order and have
the following properties:" I propose that in the next report that the expected typeclass laws for
Ord be added. They're generally agreed upon/understood. Can you spell out the concrete change to the report wording you're
suggesting? For reference, the current wording used in the 2010 Haskell
Report is quoted below. While at it, you might also want to take into
account the `Eq` class definition in the report. 6.3.2 The Ord Class class (Eq a) => Ord a where
compare :: a -> a -> Ordering
(<), (<=), (>=), (>) :: a -> a -> Bool
max, min :: a -> a -> a compare x y | x == y = EQ
| x <= y = LT
| otherwise = GT x <= y = compare x y /= GT
x < y = compare x y == LT
x >= y = compare x y /= LT
x > y = compare x y == GT -- Note that (min x y, max x y) = (x,y) or (y,x)
max x y | x <= y = y
| otherwise = x
min x y | x <= y = x
| otherwise = y The Ord class is used for totally ordered datatypes. All basic datatypes
except for functions, IO, and IOError, are instances of this class.
Instances of Ord can be derived for any user-defined datatype whose
constituent types are in Ord. The declared order of the constructors in
the data declaration determines the ordering in derived Ord instances.
The Ordering datatype allows a single comparison to determine the precise
ordering of two objects. The default declarations allow a user to create an Ord instance either
with a type-specific compare function or with type-specific == and <=
functions. _______________________________________________
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