[Haskell-beginners] Functions as Applicatives
50295 at web.de
Mon Aug 22 16:07:30 UTC 2016
I'm struggling to relate the definition of a function as a function
instance Applicative ((->) r) where
pure x = (\_ -> x)
f <*> g = \x -> f x (g x)
with the following expression
ghci> :t (+) <$> (+3) <*> (*100)
(+) <$> (+3) <*> (*100) :: (Num a) => a -> a
ghci> (+) <$> (+3) <*> (*100) $ 5
From chapter 11 of LYH http://goo.gl/7kl2TM .
I understand the explanation in the book: "we're making a function that
will use + on the results of (+3) and (*100) and return that. To
demonstrate on a real example, when we did (+) <$> (+3) <*> (*100) $ 5,
the 5 first got applied to (+3) and (*100), resulting in 8 and 500.
Then, + gets called with 8 and 500, resulting in 508."
The problem is that I can't relate that explanation with the definition
of a function as an applicative; especially f <*> g = \x -> f x (g x) .
Is (g x) the second argument to f?
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