Haskell is, and has always been, a non-strict language. *Not* a lazy language. Although many people on this list know this it is so easy to forget that it is worth repeating. Haskell is *not* a lazy language.
There are many evaluation strategies one can use to implement Haskell. The problem with the M-R is that it is a concern only in *some* of these evaluation strategies, most notably lazy evaluation. That makes the M-R such a strange thing to have in the specification of Haskell. If you read the motivation section which defines the M-R ( 4.4.5 in Haskell98 report) the report suddenly starts to talk about how many times a certain a certain _expression_ is evaluated. But nowhere in the report is it defined how expressions should be evaluated. This makes the M-R truly butt-ugly!
Some might say: Well then, let's make Haskell lazy. All implementations are lazy anyway!
No, not all implementations are lazy. And even if that were the case I think it would be a big mistake to explicitly define Haskell's evaluation order. There is a why Haskell was not specified as lazy in the first place.
But that doesn't mean that having a standardized lazy semantics for Haskell would be a bad thing. It would be a very nice thing to have an addendum to Haskell' which defined a standard lazy semantics. If it turns out that people want the M-R after all it should be placed in such an addendum, which actually talks about the evaluation order. However, I do realize that such an addendum would be quite a bit of work to put together. Perhaps after Haskell' is fixed we can start thinking about whether we have the need and the stamina to put together such a thing.
Cheers,
/Josef
_______________________________________________ Haskell-prime mailing list Haskell-prime@haskell.org http://haskell.org/mailman/listinfo/haskell-prime
