Tue, 31 Jul 2001 12:38:03 +0100, Simon Marlow pisze:

...

That's the way I'd go. You have to declare the primitive like this, BTW:

isWHNF# :: a -> (# State# RealWorld, Int# #)

because the compiler doesn't know about the IO type and you can't return a Bool directly.

It can return a Bool, e.g. ==# returns a Bool.

But ==# doesn't also return an unboxed tuple, and the code generator has special hacks to deal with primops that return enumerated types. The ==# primop actually returns an Int# which the code generator arranges to convert into a real Bool using the closure table. I guess you could return a Bool by actually indexing into the closure table, or by just returning {False,True}_static_closure. Cheers, Simon