[polyml] FFI conversions that are portable across Poly/ML versions

[Phil Clayton]

I am trying to define LargeInt.int conversions for C integer types in
terms of those supplied in Foreign in a way that will work with both
Poly/ML 5.6 or 5.7. This requires that e.g.
- Foreign.cUint64 is used for Poly/ML = 5.6 but
- Foreign.cUint64Large is used for Poly/ML >= 5.7
I am thinking of achieving this by having separate SML files for
different Poly/ML versions and using the right one as follows:

let
val version = PolyML.rtsVersion ()
in
PolyML.use (
if version >= 570
then "src-5.7.sml"
else if version = 560
then "src-5.6.sml"
else raise Fail "unsupported Poly/ML version"
)
end

Is this a future-proof way to choose based on Poly/ML version?

Another option might be to copy the implementation of these conversions
from Foreign.sml but that may not be possible - for example I couldn't
see how to get the flag bigEndian in an application.

Is there a better way altogether with some compiler trickery?

Phil

[David Matthews]

As well as PolyML.rtsVersion there are also
PolyML.Compiler.compilerVersion and
PolyML.Compiler.compilerVersionNumber. This last is probably the best
way of determining whether you have 5.6 or 5.7.

In this case, though, presumably you are really looking to see whether
"int" is LargeInt.int or not. You could use Foreign.cUint64 in 5.7 if
Poly/ML was built with arbitrary precision as default. Could you not
look at Int.maxInt and use that to decide if you need to use
Foreign.cUint64Large ?

David

Post by Phil Clayton
I am trying to define LargeInt.int conversions for C integer types in
terms of those supplied in Foreign in a way that will work with both
Poly/ML 5.6 or 5.7.  This requires that e.g.
  - Foreign.cUint64 is used for Poly/ML = 5.6 but
  - Foreign.cUint64Large is used for Poly/ML >= 5.7
I am thinking of achieving this by having separate SML files for
  let
    val version = PolyML.rtsVersion ()
  in
    PolyML.use (
      if version >= 570
      then "src-5.7.sml"
      else if version = 560
      then "src-5.6.sml"
      else raise Fail "unsupported Poly/ML version"
    )
  end
Is this a future-proof way to choose based on Poly/ML version?
Another option might be to copy the implementation of these conversions
from Foreign.sml but that may not be possible - for example I couldn't
see how to get the flag bigEndian in an application.
Is there a better way altogether with some compiler trickery?
Phil
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