I've been looking at the new Foreign structure. It is good to see that
the family of callNretM functions has been eliminated by introducing
cStar. I've updated a few examples to use the buildCall<N> functions
and they appear to work.
With CInterface, I was avoiding the family of call<N> functions by
implementing a single call function based on call_sym or
call_sym_and_convert. I am trying to do something equivalent using
Foreign.LowLevel based on the implementation in buildCall<N>withAbi.
There is a problem: the field "updateML" is not accessible because
'a conversion
is abstract. Am I right in thinking "updateML" is required for
conversions involving cStar? If so, is there a way I can implement my
own variant of a buildCall function?
Also - just an observation - in the functions buildCall<N>withAbi,
couldn't the argument offsets (and the amount of memory to malloc) be
calculated once, rather than for each foreign call? E.g. in
buildCall2withAbi:
let
val callF = callwithAbi abi [arg1Type, arg2Type] resType fnAddr
val arg1Offset = alignUp(#size resType, #align arg1Type)
val arg2Offset = alignUp(arg1Offset + #size arg1Type, #align arg2Type)
val argSize = arg2Offset + #size arg2Type
in
fn (a, b) =>
let
val rMem = malloc argSize
...
Phil
On 16/12/2015 12:35, David Matthews wrote:
There have been a few changes to the Foreign structure. The callN
functions have been renamed as buildCallN and the way functions are
passed as arguments has been changed.
The reason for the changes is to make clear that the expensive
operations are creating the C functions and closures and that calling a
C function or passing a constructed closure are comparatively cheap.
It is important to call the buildXXX functions at the top-level e.g. in
a structure, so that the C function is created once. The old callN
functions were curried and it wasn't apparent that the partial
application to the conversions was quite different to the application of
this to the arguments. For that reason the buildXXX take a tuple.
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