On Tue, Aug 11, 2009 at 3:51 PM, Robin Green<gree...@greenrd.org> wrote: > On Wed, 12 Aug 2009 11:37:02 +0200 > Peter Verswyvelen <bugf...@gmail.com> wrote: > >> Yes, sorry. >> >> But I think I already found the answer to my own question. >> >> DDC functions that are lazy don't allow side effects: >> http://www.haskell.org/haskellwiki/DDC/EvaluationOrder >> >> Anyway it would be cool if the DDC EffectSystem would also work on >> lazy functions :) > > As was just pointed out in the unsafeDestructiveAssign thread from which > this thread was forked, effects are incompatible with non-strict > evaluation.
No, they aren't. At least, they aren't in any technical way. There have been more than a few languages supporting both laziness and mutation starting with Algol. > The compiler is supposed to be able to reorder non-strict > evaluation to do optimisations, but that can't be done if effects > could happen. There's nothing special about non-strict evaluation that makes the antecedent true. Replacing "non-strict" with "strict" gives just as much of a valid statement. It is purity that allows (some) reordering of evaluation. > Also, effects would destroy modular reasoning. Again, it is purity, not laziness, that allows compositional reasoning. Effects destroy compositional reasoning in a strict language just as much. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
