This is a short note describing how I (ADR <areid@dcs.glasgow.ac.uk>)
added a new primitive operation (makeStablePtr#) to the compiler. It
serves as documentation of what I did and as a guide to anyone else
wanting to try it.

1) Change compiler/prelude/PrimOps.lhs:

   - add @MakeStablePtrOp@ to the datatype @PrimitiveOp@.

   - add the following case to @primOpInfo@

	primOpInfo MakeStablePtrOp
	  = AlgResult "makeStablePtr#" []
	[(ioWorldTy `UniFun` intPrimAndIoWorldTy), ioWorldTy]
	intPrimAndIoWorldTyCon  []
    -- makeStablePtr# :: IO_Int# -> IO_Int#
    -- == makeStablePtr# :: (IoWorld -> (Int#, IoWorld)) -> (IoWorld -> (Int#, IoWorld))

2) Change compiler/prelude/AbsPrel.lhs:

   - add @MakeStablePtrOp@ to an appropriate place in @list_of_val_assoc_lists@

     (This makes the operation visible to the programmer).

     Since this is a glasgow extension, I added it to one of
     @extra_known_vals_2@, @unboxed_ops@, @boxed_ops@. @unboxed_ops@
     is made up of several lists of operators including
     @prim_ops_used_unboxed_only@. By inspection I decided that this
     (@prim_ops_used_unboxed_only@) was the one to go for.

At this point I started recompiling the compiler - this took a long
time since the change to @PrimitiveOp@ changed the @.hi@ file
resulting in a complete (or near as makes no odds) recmpilation of the
compiler. (Is there a way of using fastmake that avoids this?

3) Change imports/StgMacros.lh to generate code for @MakeStablePtr#@

   - this is just adding a macro that calls the appropriate operation.

   (I suspect I could omit this step if I wanted since all this does
   (ahem, will do) is call a function in the runtime system.)

4) Change runtime/storage/SMap.lc to implement the new operation.

   I won't bother describing this just now.


This is a little untidy. I should perhaps add a new flag to the system
which turns my extension off and checks that it is only used in
conjunction with the Appel generational collector. But we're going to
do the same to every collector eventually aren't we?