ByteArray# as a foreign import argument?
cheng.shao at tweag.io
Thu Oct 10 20:09:42 UTC 2019
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.
>> 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
>>> -- 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
>>> 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?
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