Question

I don’t know how it’s usually called, but what I need is something like this:

f a b c = a + 2 * b + 3 * c

map f [(1,2,3), (4,5,6), (7,8,9)]

i.e. mapping list of n-tuples to a function with n separate arguments. Is there a built-in way to do this in Haskell?

P.S.: I’ve found uncurry just now, but it doesn’t seem to work this way with 3 arguments, only with 2.

Answer 1

You can define your own function:

uncurry3 :: (a -> b -> c -> d) -> (a,b,c) -> d
uncurry3 f (a,b,c) = f a b c

map (uncurry3 f) [(1,2,3), (4,5,6), (7,8,9)]

Alternatively, you can use uncurryN from the tuple package which works for tuple sizes up to 15:

cabal install tuple

import Data.Tuple.Curry

map (uncurryN f) [(1,2,3), (4,5,6), (7,8,9)]