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haskellpointfree

Triple to pair point-free way

Here is a function that multiplies the first two elements of a three-elements tuple:

f (a, b, _) = a * b

I was curious if it was possible to make this function point-free. For a pair that would be as simple as f = uncurry . (*), and if we had something like tripleToPair, that would make the solution obvious, but that function is also written the most straightforward way, via pattern matching.

I asked the almighty pointfree.io, but it returned error 500. Is that even possible? The question is purely theoretical, in my opinion, the function is good as it is.

Solution

  • The easiest way is with liftA2 (ab)using the Applicative instance for functions

    import Control.Applicative

-- This two functions are defined in module Data.Tuple.Extra from extra package
-- You could use lenses too, I guess
fst3 (a,_,_) = a
snd3 (_,b,_) = b

f = liftA2 (*) fst3 snd3