[Haskell-cafe] mapM for vectors

[Henning Thielemann]

Don Stewart schrieb:
> alexey.skladnoy:
>> Hello
>>
>> I found that there is no monadic map for vector. It's possible to define to 
>> define such map using conversion to list, but I suppose it's not efficient. I 
>> didn't make any measurements.
>>
>>> mapM' :: Monad m => (a -> m b) -> V.Vector a -> m (V.Vector b)
>>> mapM' f = return . V.fromList <=< mapM f . V.toList
>> Any suggestions about implementation of such function? 
>> Specifically I want to use Random monad.
>>
> 
> 
> There's a tutorial here on usving vectors,
> 
>     http://haskell.org/haskellwiki/Numeric_Haskell:_A_Vector_Tutorial#Random_numbers
> 
> mapM is available via Fusion.Stream.Monadic.mapM

But can it be efficient? It must handle cases like  m = []  and thus
creation of the (V.Vector b) result means a lot of copying, right?