[Haskell-cafe] Convert Data.Vector.Unboxed.Mutable.MVector to Data.Vector.Unboxed.Vector

[Cody Goodman]

Thanks! I'll try it out in a bit.

On Aug 5, 2017 10:32 PM, "Amos Robinson" <amos.robinson at gmail.com> wrote:

> Yes, I believe Data.Vector.Generic.freeze will work. But I would use the
> one from Data.Vector.Unboxed unless you really need the generic version.
> Sometimes the extra constraints in the generic version can be a bit
> cumbersome, requiring extra type annotations where the specific versions
> don't.
>
> On Sun, 6 Aug 2017 at 13:22 Cody Goodman <codygman.consulting at gmail.com>
> wrote:
>
>> I'm not back at a computer yet, but so I and others reading these
>> archives in the future know: Does that mean that freeze from
>> Data.Vector.Generic.freeze should work for me then?
>>
>> On Sat, Aug 5, 2017 at 10:05 PM, Amos Robinson <amos.robinson at gmail.com>
>> wrote:
>>
>>> Mutable is the type family from Vector to MVector. So the result type
>>> will be an instance of Vector, but the input MVector doesn't need to be.
>>> It's a little confusing that freeze is in Data.Unboxed.Vector, not
>>> .Mutable: https://hackage.haskell.org/package/vector-0.
>>> 12.0.1/docs/Data-Vector-Unboxed.html#v:freeze
>>>
>>> On Sun, 6 Aug 2017 at 12:59 Cody Goodman <codygman.consulting at gmail.com>
>>> wrote:
>>>
>>>> I see the type is:
>>>>
>>>> freeze :: (PrimMonad
>>>> <https://hackage.haskell.org/package/primitive-0.6.2.0/docs/Control-Monad-Primitive.html#t:PrimMonad>
>>>> m, Vector
>>>> <https://hackage.haskell.org/package/vector-0.12.0.1/docs/Data-Vector-Generic.html#t:Vector>
>>>> v a) => Mutable
>>>> <https://hackage.haskell.org/package/vector-0.12.0.1/docs/Data-Vector-Generic.html#t:Mutable>
>>>> v (PrimState
>>>> <https://hackage.haskell.org/package/primitive-0.6.2.0/docs/Control-Monad-Primitive.html#t:PrimState>
>>>> m) a -> m (v a)
>>>>
>>>>
>>>> So there is a Vector constrant that MVector will not have. Does the
>>>> Mutable type family get around this somehow?
>>>>
>>>>
>>>> There doesn't seem to be a freeze function specifically for
>>>> Data.Vector.Unboxed.Mutable.MVector listed at:
>>>> https://hackage.haskell.org/package/vector-0.12.0.1/docs/
>>>> Data-Vector-Unboxed-Mutable.html
>>>>
>>>> Thanks,
>>>>
>>>> Cody
>>>>
>>>> On Sat, Aug 5, 2017 at 9:56 PM, Amos Robinson <amos.robinson at gmail.com>
>>>> wrote:
>>>>
>>>>> I think you want "Data.Vector.Generic.freeze", or unsafeFreeze if you
>>>>> are sure you won't modify the mutable vector after making it immutable.
>>>>> https://hackage.haskell.org/package/vector-0.12.0.1/docs/
>>>>> Data-Vector-Generic.html#v:freeze
>>>>>
>>>>> On Sun, 6 Aug 2017 at 12:46 Cody Goodman <
>>>>> codygman.consulting at gmail.com> wrote:
>>>>>
>>>>>> I want to do this so I can use the Data.Vector.Unboxed.Generic
>>>>>> functions requiring the Vector constraint, namely the maxIndex function.
>>>>>> Implementing maxIndex for Data.Vector.Unboxed.Mutable.MVector would
>>>>>> be useful as well, but I'm even more confused at how to do that or where to
>>>>>> begin.
>>>>>>
>>>>>> Here is some stubbed out code demonstrating this.
>>>>>>
>>>>>> {-# Language ScopedTypeVariables #-}
>>>>>> module Main where
>>>>>>
>>>>>> import Control.Monad.Primitive
>>>>>> import qualified Data.Vector.Unboxed
>>>>>> import qualified Data.Vector.Generic as VG
>>>>>> import qualified Data.Vector.Unboxed.Mutable as VM
>>>>>> import qualified Data.Vector.Unboxed as V
>>>>>>
>>>>>> toImmutable :: VM.MVector RealWorld Int -> V.Vector Int
>>>>>> toImmutable = undefined
>>>>>>
>>>>>> main :: IO ()
>>>>>> main = do
>>>>>>   v :: VM.MVector RealWorld Int <- VM.new 1
>>>>>>   VM.write v 0 (3 :: Int)
>>>>>>   x <- VM.read v 0
>>>>>>   -- y <- VG.head . toImmutable $ v
>>>>>>   -- print y
>>>>>>   print $ VM.length v
>>>>>>
>>>>>> {-
>>>>>> Thanks,
>>>>>>
>>>>>>
>>>>>> Cody
>>>>>> -}
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>>>>>
>>>>>
>>>>
>>
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