On Wed, Jul 07, 2004 at 01:18:54PM +0100, Graham Klyne wrote:
There's a pattern of higher-order function usage I find myself repeatedly wanting to use, exemplified by the following:
[[
-- combineTest :: (Bool->Bool->Bool) -> (a->Bool) -> (a->Bool) -> (a->Bool)
combineTest :: (b->c->d) -> (a->b) -> (a->c) -> a -> d
combineTest c t1 t2 = \a -> c (t1 a) (t2 a)
(.&.) :: (a->Bool) -> (a->Bool) -> (a->Bool)
(.&.) = combineTest (&&)
(.|.) :: (a->Bool) -> (a->Bool) -> (a->Bool) (.|.) = combineTest (||)
The operators can be also defined as follows: (.&.) f g x = (f x) && (g x) (.|.) f g x = (f x) || (g x)
It is clear from these definitions, that the operators are ternary operators.
As operators are essentially the same as functions, in Haskell, any number of parameters can be given in an operator definition.
Henk-Jan van Tuyl
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