On Mon, Nov 06, 2006 at 01:53:52PM +0000, Malcolm Wallace wrote: > So the doubly bizarre thing is that, actually, `seq` does not control > the evaluation order (which is the only valid reason for wanting to use > it in the first place), but nevertheless it undesirably changes the > semantics of programs such that equational reasoning no longer holds.
When I've used seq, it's to ensure that a function is strict in that argument, and therefore has been evaluated before the function is called. (If the language had unlifted types, I might have used those instead). Beyond that, I don't care exactly when it was evaluated; it might be long before, thanks to propagation of strictness information. seq has a clear denotational semantics. One can still do equational reasoning with it, though there will be side conditions about whether something is _|_ or not. The downside is that the eta rules get such side conditions, and polymorphic seq greatly weakens parametricity. Apart from that, the only thing wrong with seq is its name. _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
