Thu, 12 Jul 2001 17:59:31 +0200 (MET DST)
The topic is fixity declarations for operators.
The report says:
"Fixity is a property of a particular entity (constructor
or variable), just like its type; fixity is not a
property of that entity's name."
It is possible to define fixities for locally declared
f x y z = x # y # z
infixr 4 #
a # b = a `div` b
The use of (#) in the body of g is right associative.
However, it is not possible to define the fixity of an
operator which is an argument to a function. If I define:
foldr4 :: (a -> b -> b) -> b -> (a,a,a,a) -> b
foldr4 (#) z (a,b,c,d) = a # b # c # d # z
I will have to put in parentheses explicitly, because it is
not possible to define the fixity of that entity (namely the
argument (#) to foldr4).
In this case, (#) gets the default fixity, namely infixl 9.
Apart from the fact if we want to allow this or not, I think
the report should be clear about that it is not possible to
define the fixities of locally bound operator names in this