[Haskell-cafe] How to understand the 'forall' ?

[zaxis]

Isnot it clear without the 'forall' ?
data Branch tok st a = Branch (PermParser tok st (b -> a)) (GenParser tok st
b)

thanks!


jkff wrote:
> 
> This means that for any type 'b' you can construct a value of type
> 'Branch tok st a' by passing to Branch an argument of type
> '(PermParser tok st (b -> a))' and 'GenParser tok st b'.
> This also means that when you're given a value of type Branch tok st
> a, you don't know what that 'b' type was; the only thing you know is
> that the 'b' in 'b -> a' in the first argument of Branch is the same
> as the 'b' in 'GenParser tok st b'.
> 
> See also: the haskellwiki page on existential types.
> 
> 2009/9/2 zaxis <z_axis at 163.com>:
>>
>> data Branch tok st a = forall b. Branch (PermParser tok st (b -> a))
>> (GenParser tok st b)
>>
>> please shed a light on me, thanks!
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> 
> 
> 
> -- 
> Eugene Kirpichov
> Web IR developer, market.yandex.ru
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