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What are these operators doing?
(.) :: (b -> c) -> (a -> b) -> a -> c
(<$>) :: Functor f => (a -> b) -> f a -> f b
(<*>) :: Applicative f => f (a -> b) -> f a -> f b
I don't have any idea when I see the signatures. Perhaps some example with a simple and easy to understand explanation will help me.
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in goes along with let to name one or more local expressions in a pure function. would print "hello world". And you just need one in before you use the names you just defined. And these names definitely don't have to be used as parameters to a function -- they can be just about anything, even functions themselves!
In general terms, where f and g are functions, (f . g) x means the same as f (g x). In other words, the period is used to take the result from the function on the right, feed it as a parameter to the function on the left, and return a new function that represents this computation."
In Haskell it is just another character to distinguish identifiers and the identifier is then called fold prime , but it is commonly used in the same way as it used in mathematics. Save this answer.
fmap is used to apply a function of type (a -> b) to a value of type f a , where f is a functor, to produce a value of type f b . Note that for any type constructor with more than one parameter (e.g., Either ), only the last type parameter can be modified with fmap (e.g., b in `Either a b`).
I am also learning Haskell, and my recommendation is to have a look into Learn You a Haskell for Great Good!, and more precisely:
(.) read Function composition
<$> and <*> read Applicative functors
In essence:
(.) is function composition: if you have g :: a -> b and f :: b -> c then f . g is essentially f(g(x)): first use g on an a to get a b and then use f on that b to get a c
<$> takes a function taking an a and returning a b, and a functor that contains an a, and it returns a functor that contains a b. So <$> is the same as fmap :: (a -> b) -> f a -> f b
<*> takes a functor that contains a function taking an a and returning a b, and a functor that contains an a, and it returns a functor that contains a b. So <*> kind of extract the function from a functor and applies it to an arguments also inside a functor, and finally returns the result into a functor
Note the explanations that you find in the book chapters are better than my attempt above
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