Simon Marlow wrote: > > Malcolm Wallace writes: > > But the whole purpose of 'interact' is to use its argument as the > > demanding function which drives lazy consumption of the input. It is > > *designed* to reveal the evaluation behaviour, by hoisting it into > > the I/O monad. > > This is why interact is bad, IMO: it forces you to think about the > evaluation order. The evaluation order for Haskell is not part of the > language definition - it is normally up to the implementation to pick a > strategy. > > Except when you get to lazy I/O. The commonly accepted meaning for the > lazy I/O operations forces the implementation to adopt a lazy evaluation > strategy for values which require lazy I/O. For example, eager > evaluation would be a completely valid implementation strategy for > Haskell if it were not for lazy I/O.
Pardon? Haskell is a non-strict language. Using 'interact' is one of numerous situations where one takes advantage of non-strict semantics. (Keith just gave a different example.) Non-strict semantics does not prescribe the evaluation order, although usually lazy evaluation is used. I suppose you are talking about optimistic evaluation, which is a mixture of eager and lazy evaluation. That is fine and should work well with 'interact', otherwise there is something wrong with optimistic evaluation. Certainly pure eager evaluation is not a valid evaluation strategy for Haskell. Olaf -- OLAF CHITIL, Dept. of Computer Science, The University of York, York YO10 5DD, UK. URL: http://www.cs.york.ac.uk/~olaf/ Tel: +44 1904 434756; Fax: +44 1904 432767 _______________________________________________ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
