[project @ 1999-05-28 19:21:34 by simonpj]

Make the default instance for Ord such that it suffices to define <=, as claimed

diff --git a/ghc/lib/std/PrelBase.lhs b/ghc/lib/std/PrelBase.lhs
index 9cd1c88..744f8a6 100644 (file)
--- a/ghc/lib/std/PrelBase.lhs
+++ b/ghc/lib/std/PrelBase.lhs
@@ -30,7 +30,7 @@ infixr 0  $
 
 %*********************************************************
 %*                                                     *
-\subsection{Standard classes @Eq@, @Ord@, @Bounded@
+\subsection{Standard classes @Eq@, @Ord@}
 %*                                                     *
 %*********************************************************
 
@@ -50,7 +50,9 @@ class  (Eq a) => Ord a  where
 -- Using compare can be more efficient for complex types.
     compare x y
            | x == y    = EQ
-           | x <  y    = LT
+           | x <= y    = LT    -- NB: must be '<=' not '<' to validate the
+                               -- above claim about the minimal things that can
+                               -- be defined for an instance of Ord
            | otherwise = GT
 
     x <= y  = case compare x y of { GT -> False; other -> True }
@@ -241,7 +243,7 @@ some programs may get away without consulting PrelTup).  Furthermore,
 the renamer currently *always* asks for () to be in scope, so that
 ccalls can use () as their default type; so when compiling PrelBase we
 need ().  (We could arrange suck in () only if -fglasgow-exts, but putting
-it here seems more direct.
+it here seems more direct.)
 
 \begin{code}
 data  ()  =  ()