On 08/01/15 10:00, Edward Z. Yang wrote:
For posterity, the answer is no, and it is explained in this comment: https://ghc.haskell.org/trac/ghc/ticket/5129#comment:2
Thanks, this is helpful. So we have three potential implementations for evaluate: (1) \x -> return $! x (2) \x -> (return $! x) >>= return (3) implemented using seq# (1) and (2) are supposed to be equivalent (by the monad law), but are not in reality, since in (2) evaluate x is always a value. The documentation for 'evaluate' talks about the difference between (1) and (2). Furthermore, it suggests that (2) is a valid implementation. (1) is buggy, as explained in #5129 linked above. However, it doesn't say anything about (2). Would (2) still suffer from #5129? In that case, the docs should be fixed. Also, where can I find the 'instance Monad IO' as understood by GHC? grep didn't find one. Roman