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Alex Rivera
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I'm eyeing functors, applicative functors… I'm not sure how to get where I want, but I have the feeling that following the types should get me closer. Is there a simple way to make a map -alike which only applies to the first element of a 2-tuple? Taking first from Control.Arrow and using Arrow (->) , this does the trick nicely: map . first :: (b -> c) -> [(b, d)] -> [(c, d)] My only concern is that I have yet to gain a real intuition for arrows, and so I'll probably find myself in deep water sooner or later if I keep this up. Plus, this seems to be a rather convenient case that can't be generalised. Can I get the same functionality by using something from functors, monads or whatever else, while getting to the heart of what I want? I was toying around with \f -> map (f `on` fst) -like ideas, but couldn't quite get there.
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