ByteArray# as a foreign import argument?

[Sylvain Henry]

Or better 98668305453ea1158c97c8a2c1a90c108aa3585a (2001):

 From the commit message:

     - finally, remove the last vestiges of ByteArray and MutableByteArray
       from the core libraries.  Deprecated implementations will be 
available
       in the lang compatibility package.


On 11/10/2019 10:32, Sylvain Henry wrote:
> > But I can't find such a ByteArray type definition in today's common 
> packages. What's the rationale for this piece of code?
>
> Doing some archeology they seem to have been removed from 
> ghc/lib/std/PrelArr.lhs in e921b2e307532e0f30eefa88b11a124be592bde4 
> (1999):
>
>  data Ix ix => Array ix elt        = Array            ix ix (Array# elt)
> -data Ix ix => ByteArray ix          = ByteArray ix ix ByteArray#
>  data Ix ix => MutableArray     s ix elt = MutableArray     ix ix 
> (MutableArray# s elt)
> -data Ix ix => MutableByteArray s ix     = MutableByteArray ix ix 
> (MutableByteArray# s)
>
> So it's probably dead code since then.
>
> Cheers,
> Sylvain
>
>
> On 10/10/2019 21:15, Shao, Cheng 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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