Re: ByteArray# as a foreign import argument?

I've just manually checked with a `data ByteArray = ByteArray Int Int ByteArray#` example, indeed GHC doesn't support marshalling it. That being said, I'm still curious about the meaning of that blob of code I've just pasted. On Fri, Oct 11, 2019 at 5:28 AM chessai . wrote:

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 wrote:

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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 wrote:

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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 wrote:

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It's a primitive type. https://gitlab.haskell.org/ghc/ghc/blob/master/compiler/prelude/primops.txt.... https://gitlab.haskell.org/ghc/ghc/wikis/commentary/prim-ops

Cheers, Csaba

On Thu, Oct 10, 2019 at 8:16 PM Shao, Cheng wrote:

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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#L...):

``` -- 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 _______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs

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