[Haskell-cafe] What does the `forall` mean ?

[Andrew Coppin]

David Virebayre wrote:
> On Thu, Nov 12, 2009 at 8:52 PM, Andrew Coppin
> <andrewcoppin at btinternet.com> wrote:
>
>   
>> I just meant it's not immediately clear how
>>     
>
>   
>>  foo :: forall x. (x -> x -> y)
>>     
>
>   
>> is different from
>>     
>
>   
>> foo :: (forall x. x -> x) -> y
>>     
>
>   
>> It takes a bit of getting used to.
>>     
>
> That still confuses me.
>   

The difference is when the x variable gets bound - but to comprehend 
that, you have to realise that x gets bound at some point, which is 
non-obvious...