I mildly prefer 'Idempotent' to 'Dupable'. feels more descriptive to me. This is even useful in jhc without threading, as expressions can be marked 'idempotent and cheap' giving the compiler freedom to duplicate them when it makes sense. However, I am worried about the 'Inline' in the other one, in jhc, unsafePerformIO is always inlined, it uses a different trick (my 'dependingOn' primitive) to ensure the world is not unified with another one. Can we come up with a term that describes the difference other than 'inline' as that is a ghc specific quirk. incidentally, jhc has another form of unsafePerformIO that does not wrap its argument in a new exception handler. It can be used when you know the argument won't raise an ioError or if it does, it handles them itself. (normal calls to things like error and pattern match failures are fine. it is just haskell98 io errors that metter for this one) John -- John Meacham - ⑆repetae.net⑆john⑈