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

[Mateusz Kowalczyk]

Oops, you're right. Sorry for my oversight.

On 13/02/13 08:12, Ertugrul Söylemez wrote:
> Mateusz Kowalczyk <fuuzetsu at fuuzetsu.co.uk> 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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