Hmm, of course I meant:
class Assignable x where
(=) :: x -> x -> IO ()
class Assignable_Const x where
(=) :: x -> Const x -> IO ()
Keean.
On 9 January 2015 at 08:55, Keean Schupke <[email protected]> wrote:
> They do need to be part of the type system because their misuse leads
>> to unsoundness, but requiring that different classifications of
>> mutability be distinct types seems to lead to awkwardness when you're
>> just trying to implement something with reasonable variance over
>> mutability.
>
>
> Surely you just need a 'const' type as in C++, and if you cannot cast away
> const (you can only cast to const) it seems safe.
>
> So:
>
> instance Assignable x where
> (=) :: x -> x -> IO ()
>
> instance Assignable x where
> (=) :: x -> Const x -> IO ()
>
> then:
>
> Const Int // immutable value
> Const (Pointer Int) // an immutable pointer to a mutable value
> Pointer (Const Int) // a mutable pointer to an immutable value
> etc...
>
>
> Keean.
>
>
>
>
>
>
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