Re: [Haskell-beginners] f . g or f g or f $ g?

Oops, you're right. Sorry for my oversight. On 13/02/13 08:12, Ertugrul Söylemez wrote:

Mateusz Kowalczyk wrote:

...

A less obvious interpretation is to treat ($) as `id'.

(f . g) x = f $ g x = f (id g x) = f (g x)

This is not how you get from ($) to id. The correct path is:

f $ x = ($) f x = f x = id f x = f `id` x

This equivalence is indicated by the type of ($). It's a specialized instance of a -> a:

($) :: (a -> b) -> (a -> b) ($) f = f

or equivalently:

($) :: (a -> b) -> a -> b ($) f x = f x

or equivalently:

($) :: (a ~ b -> c) => a -> a ($) = id

Greets, Ertugrul

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