Answering my own question, one can achieve the goal via doing a lookup, if
the number of possible parameters is limited.
eg. assume add is a function which can only take Int's from [0..9].
Interestingly, my situation is exactly like this. I think I'll implement
such a lookup.
The question is still open though, if somebody has some magic to extract the
prameter from an applied function...
2009/11/28 Ozgur Akgun
Sorry, no good.
I don't want to guess the first paramater, I really want to access it.
2009/11/28 Steffen Schuldenzucker
Ozgur Akgun wrote:
Hi cafe,
Is such a thing possible,
add :: Int -> Int -> Int add x y = x + y
-- a list of partially applied functions adds = [add 3, add 5, add 7, add 3, add 5, add 8]
-- an example usage of the list k = map (\ f -> f 10 ) adds
add3s = filter (?) adds -- add3s = [add 3, add 3] addEvens = filter (?) adds --addEvens = [add 8]
I want to have functions in place of the ? signs. I guess one would need a way of extracting the applied value from a partially applied function (or totally, doesn't matter)
Well, sure you can:
add3s = filter (\f -> f 0 == 3) adds addEvens = filter (\f -> isEven $ f 0) adds
This is only possible since there is that special property of the addition that (add a) 0 == a forall a, i.e. you can extract the first parameter back out of the partial applied function by passing 0 as a second parameter.
It clearly depends on the function how much information about the parameters can be read from the result.
-- Steffen
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-- Ozgur Akgun
-- Ozgur Akgun