John Meacham wrote:
On Fri, Feb 03, 2006 at 07:33:12PM -0000, Brian Hulley wrote:
One question is how to get some kind of "do" notation that would work well in a strict setting. The existing "do" notation makes use of lazyness in so far as the second arg of >> is only evaluated when needed. Perhaps a new keyword such as "go" could be used to use >>= instead ie:
you can override (>>) in your monad
instance Monad ... where a >> b = a `seq` b `seq` (a >>= \_ -> b) ....
unless I am misunderstanding what you want.
John
If strictness was the default (eg if the language were ML not Haskell), then in putStr "hello" >> putStr (show 1) both args to >> would be evaluated before >> was called. Thus putStr (show 1) would be evaluated before the combined monad is actually run, which would be wasteful if we were using a monad with a >> function that only runs the rhs conditionally on the result of the lhs. If Haskell were a strict language I think an equivalent for the do notation would have to lift everything (except the first expression) and use >>= instead of >> . Regards, Brian.