ByteArray# as a foreign import argument?

[chessai .]

Can you do that? I know with the UnliftedFFI you can use ByteArray# and if
you have something like uint8_t*, it will make sure that the pointer lines
up with the payload of the ByteArray#. You could always just wrap it in
Data.Primitive.ByteArray.ByteArray, no? That is to say, I don't think GHC
can do what you're asking.

On Thu, Oct 10, 2019, 4:10 PM Shao, Cheng <cheng.shao at tweag.io> wrote:

> Yes, and specifically, the lifted ByteArray type as described in the
> comments, not the unlifted ByteArray# type.
>
> On Fri, Oct 11, 2019 at 4:00 AM Csaba Hruska <csaba.hruska at gmail.com>
> wrote:
> >
> > Sorry, maybe I got it wrong. Are you asking if is there any package that
> passes ByteArrays via FFI?
> >
> > On Thu, Oct 10, 2019 at 8:54 PM Csaba Hruska <csaba.hruska at gmail.com>
> wrote:
> >>
> >> It's a primitive type.
> >>
> https://gitlab.haskell.org/ghc/ghc/blob/master/compiler/prelude/primops.txt.pp#L1388
> >> https://gitlab.haskell.org/ghc/ghc/wikis/commentary/prim-ops
> >>
> >> Cheers,
> >> Csaba
> >>
> >> On Thu, Oct 10, 2019 at 8:16 PM Shao, Cheng <cheng.shao at tweag.io>
> wrote:
> >>>
> >>> Hello devs,
> >>>
> >>> I've been trying to figure out how to pass lifted types as foreign
> >>> types, then encountered the following code in the `DsCCall` module
> >>> (
> https://gitlab.haskell.org/ghc/ghc/blob/master/compiler/deSugar/DsCCall.hs#L172
> ):
> >>>
> >>> ```
> >>>   -- Byte-arrays, both mutable and otherwise; hack warning
> >>>   -- We're looking for values of type ByteArray, MutableByteArray
> >>>   --    data ByteArray          ix = ByteArray        ix ix ByteArray#
> >>>   --    data MutableByteArray s ix = MutableByteArray ix ix
> >>> (MutableByteArray# s)
> >>>   | is_product_type &&
> >>>     data_con_arity == 3 &&
> >>>     isJust maybe_arg3_tycon &&
> >>>     (arg3_tycon ==  byteArrayPrimTyCon ||
> >>>      arg3_tycon ==  mutableByteArrayPrimTyCon)
> >>>   = do case_bndr <- newSysLocalDs arg_ty
> >>>        vars@[_l_var, _r_var, arr_cts_var] <- newSysLocalsDs
> data_con_arg_tys
> >>>        return (Var arr_cts_var,
> >>>                \ body -> Case arg case_bndr (exprType body) [(DataAlt
> >>> data_con,vars,body)]
> >>>               )
> >>> ```
> >>>
> >>> It seems we allow a "ByteArray" type as a foreign import argument, if
> >>> the third field of the datacon is a ByteArray# or MutableByteArray#.
> >>> But I can't find such a ByteArray type definition in today's common
> >>> packages. What's the rationale for this piece of code?
> >>>
> >>> Cheers,
> >>> Cheng
> >>> _______________________________________________
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