[Switching to Haskell-cafe] At 11:26 22/11/04 +0000, you wrote:
I would ask an alternative question - is it possible to live without unsafePerformIO? I have never needed to use it!
I have used it once, with reservations, but at the time I didn't have the time/energy to find a better solution. (The occasion of its use was accessing external entities within an XML parser; by making the assumption that the external entities do not change within any context in which results from a program are compared, I was able to satisfy the "proof obligation" of not causing or being sensitive to side effects.) The reason this was important to me is that I wanted to be able to use the parser from code that was not visibly in the IO monad. For me, treating Web data transformations as pure functions is one of the attractions of using Haskell. (Since doing that, I had an idea that I might be able to parameterize the entity processing code on some Monad, and use either an Identity monad or IO depending on the actual requirements. This way, I could keep pure XML processing out of the IO monad, but use IO when IO was needed.) In short: I think it's usually possible to avoid using unsafePerformIO, but I'd be reluctant to cede it altogether, if only for sometimes quick-and-dirty pragmatic reasons. #g ------------ Graham Klyne For email: http://www.ninebynine.org/#Contact