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

[Cody Goodman]

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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