On Sat, Jul 07, 2007 at 02:20:49PM -0400, Samuel Bronson wrote:
First of all, I'm wondering what the intended uses of the lookupCType and lookupCType' functions are. It seems like lookupCType tells you the type that should be used in marshalling a type, and lookupCType tells you the primitive type that is used in the representation of a type as well as how to extract the value from it. I'm not sure how to go from there to actually converting to/from the correct primitive type to use in interfacing with C code...
A lot of this is due to history and a very major rewrite of jhc internals, switching everything from a C based view of the world to a c-- (or assembly) one. It used to be that raw haskell types (basic numeric types) were associated with a specific C type, such as 'int' and all that entails, so things like 'int', 'unsigned', 'wchar_t', etc were all independent types, treated as opaque by jhc threading their way all through the system from source to code generation and the actual operations performed such as unsigned multiply vs signed were affected by the type. Also, when this system was in place, first class unboxed values did not exist, requiring the creation of data/primitives.txt to provide a mapping of C primitive types to haskell types so it can build the proper instances constructors etc as appropriate. In addition, this type determined the C calling convention used. so the then aptly named 'lookupCType' functions basically took a name, and looked up the info in the appropriate primitive tables and whatnot. needless to say, this situation although nice and straightforward at first, was quite problematic, there were lots of things like casting from 'wchar_t' to 'int' inhibiting optimizations. you would have to cast a value explicity in order to do a signed operation on it instead of an unsigned one. You could not vary the calling convention used in FFI calls independent of the type, for instance, you mich want 'Char' to translate to a 'wchar_t' calling convention, even though you don't want 'wchar_t' to be the representation used for 'Char'. Thus C/Op.hs and friends were born. now, primitive types are fully specified and all operations are spelt out explicitly. rawTypes no longer coorespond to C types, but rather a well defined internal format such as 'bits32' and all operations are fully specified (signed multiply and unsigned multiply are independent operations, as are floating point vs non floating point, etc) however, rather than change the E representation of types, a rawtype now _must_ contain a serialized version of a C-- type, not a C type like they used to have in them. The mapping of names used in foreign declarations to the calling convention is now indpendent of the haskell representation of the type, this is very nice for when a type is a newtype of another and actually represents a different C value. however, this change is very recent and there is still a lot of code around that refers to C types, and old tables for looking up properties of C types that arn't used anymore. the lookupCType functions will be replaced by nicer more explicit querying operations. The C type used in the calling convention is what is actually stored in the ExtType parameter in C/Prim and is completly independent of the E or Grin type and only comes up again in code generation. explicit casts are not needed because the code generator knows how to do so and there may be no analog of the C type in grin or E (in fact, C may never come into play if using a native code generator)
Another question is: what sort of E type should an imperative foreign export use? Consider:
foreign export hello :: Int -> IO () hello n = putStrLn ("Hello, "++show n)
foreign export foo :: IO Int foo :: Num a => IO a foo = return 1
Should they just use IO? I guess that's what main does...
I am not sure what you mean. foreign exports are 'metainfo' and need not affect anything at all until code generation when a proper alias or exported symbol is emitted by the code generator. (gcc provides a way to create explicit aliases, but gcc inlining should make that moot) for that case, since you can't export 'foo' directly (having a different type), a placeholder function should be generated in the compiler private namespace. something like F@.fMain.foo = foo Int then F@.fMain.foo would be annotated with the proper foreign export declaration. I don't think IO ever needs to be treated specially other than setting the IOLike flag properly and making sure the world argument is added in the right spot. John -- John Meacham - ⑆repetae.net⑆john⑈