[Haskell] TArray?

Sebastian Sylvan sebastian.sylvan at gmail.com
Tue Dec 13 12:09:55 EST 2005

On 12/13/05, Simon Marlow <simonmar at microsoft.com> wrote:
> On 13 December 2005 13:11, Sebastian Sylvan wrote:
> > On 12/13/05, Tomasz Zielonka <tomasz.zielonka at gmail.com> wrote:
> >> On Tue, Dec 13, 2005 at 01:32:46PM +0100, Sebastian Sylvan wrote:
> >>> Are there plans to include a mutable array for use in the STM monad,
> >>> or a good reason for why this is not needed? Also, an unboxed
> >>> version would be nice.
> >>
> >> Why not use an (Array idx (TVar a)) ?
> >
> > Ah.. Good thinking!
> > This should work for in the STM monad for anything you would IOArray
> > for in the IO monad,  if you write proper instances for MArray of
> > course...
> >
> > It's a bit inefficient, an extra indirection (compared to a primitive
> > implementation) but that shouldn't matter too much for the general
> > case. And the TVars themselves introduces some extra overhead, I would
> > suppose (which could be per-array rather than per-element, without
> > losing the property that only writes to the same element causes
> > retries).
> > It gets even trickier if you want an unboxed mutable array in the STM
> > monad.
> >
> > But still, it's useful and I think a mutable array for the STM monad
> > should be in the libraries. It could be implemented as an Array at
> > first, and perhaps later switch to a more efficient representation.
> In the past I have used arrays of TVars, as Thomasz suggested.  It would
> indeed be better to have a primitive STM array, the only problem with
> this is the extra complexity.  One simplifying assumption is that it
> should consider changes at the level of the whole array, rather than
> per-element (otherwise you'd use an array of TVars).

There is no plan to provide an implementation of this (the
Array-of-TVar approach) in the libs? With an MArray instance?
It would be nice if you could just plug i into existing functions
operating on MArray...


Sebastian Sylvan
UIN: 44640862

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