[CakeML-dev] Array library

[Ramana Kumar]

I don't see how it matters much. So go with the easiest then.

On 14 April 2017 at 02:55, Scott Owens <S.A.Owens at kent.ac.uk> wrote:

> That’s also the hardest option to implement, since it involves changing
> the structure of the source_to_mod proof. I currently favour adding an
> empty array allocation primitive because I think it is the easiest option.
>
> Scott
>
> > On 2017/04/13, at 07:16, Ramana Kumar <Ramana.Kumar at cl.cam.ac.uk> wrote:
> >
> > I prefer making fromList and tabulate primitives. Maybe some day they
> could then be more efficient primitives than the obvious implementation in
> source_to_mod. The other two options seem to make empty arrays too special.
> >
> > On 13 April 2017 at 01:44, Scott Owens <S.A.Owens at kent.ac.uk> wrote:
> > At the moment we define Array.fromList and Array.tabulate as follows,
> which is operationally correct, but the type inferencer gives them types
> that are too specific: int list -> int array and int -> (int -> int) -> int
> array.
> >
> >   fun fromList l =
> >     let val arr = array (List.length l) 0
> >       fun f l i =
> >        case l of
> >           [] => arr
> >         | (h::t) => (update arr i h; f t (i + 1))
> >     in f l 0 end
> >
> >  fun tabulate n f =
> >     let val arr = array n 0
> >       fun u x =
> >         if x = n then arr
> >         else (update arr x (f x); u (x + 1))
> >     in
> >       u 0
> >     end
> >
> > This is because of the initialisation of the array to 0, before
> overwriting all of the 0s with the real values. Now I can update the code
> to initialise the array with one of the values that will go into the array
> (the head of the list, and f 0, for example). However, this is not possible
> for fromList [] and tabulate 0, which both produce empty arrays, and the
> type of the contents are not constrained. I can see several ways to fix
> this, but none are great.
> >
> > - Make fromList and tabulate be primitives in the source semantics
> (which could be implemented in source_to_mod rather than a later phase).
> > - Add a new array_empty primitive with type unit -> ‘a array
> > - Make an attempt to create an empty array raise an exception
> >
> > Any preferences?
> >
> > Scott
> > _______________________________________________
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> > Developers at cakeml.org
> > https://lists.cakeml.org/listinfo/developers
> >
>
>
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