On Thu, Jan 12, 2012 at 12:54 AM, Simon Marlow
For boxed arrays you need a PrimOp of course (like catMutVar#). For unboxed arrays you could get away with FFI, but a PrimOp would be better because it could be inline. But to get it inline would mean modifying the native and LLVM backends to support CAS operations.
If I were you I would use FFI for now. The cost of the out-of-line call is much less than the cost of the CAS anyway. A gcc dependency is not a big deal, it's available on all Unix-like platforms and I don't see us removing it from the Windows installs any time soon.
In a recent project (http://hackage.haskell.org/package/ekg) I found myself wanting unboxed mutable integers with CAS semantics (to implement simple counters). What would be required to support (1) unboxed mutable variables, and (2) CAS semantics for these. I guess (2) is easy once you have (1). Just add some new primops. -- Johan