Ticket #5931 (closed feature request: fixed)
Allow 'Any' to be passed to a foreign prim function.
|Reported by:||nomeata||Owned by:||simonmar|
|Type of failure:||None/Unknown||Difficulty:||Unknown|
|Test Case:||Blocked By:|
Real primops can take boxed arguments, and the Cmm code will receive the pointer to the object on the Haskell heap, e.g. for unpackClosure#. To be able to implement such a function in a "foreign prim" call, this needs to be allowed there as well, and the attached patch does that.
By only allowing Any here (instead of arbitrary types), it is clearer that the function will not receive the value in any marshalled form, but just the raw pointer. Haskell code using such functions are likely to use unsafeCoerce# to turn a Haskell value into a value of type Any.
I am working on code that helps investigating the heap, similar to vacuum, and unwrapClosure was not sufficient. With this patch in GHC I do not have to modify the compiler further to create an improved version.
If applied, the documentation at wiki:Commentary/PrimOps#Foreignout-of-linePrimOps needs to be updated. I did not find any documentation in the GHC tree to updated accordingly.