On February 21, 2011 08:15:38 Tyson Whitehead wrote:
The non-deterministic semantics
??? _|_ x -> possibly _|_ or x
are also pretty interesting. Very reminiscent of what can happen with rewrites in the presence of the other two. Could there be something here (i.e., this would allow you to have rewrites that still preserve the semantics as the non-determinism would officially be part of the semantics)?
To clarify a bit more. Traditionally, I believe the problem is you use seq in some function f. Appearing in some composition g, f results in the semantics g _|_ /= a There is a rewrite that either you or the compiler would like to perform on the composition g to give g', but due to seq/pseq in f you windup with g' _|_ = _|_ (or the other way around). If we are using ??? instead of seq/pseq, however, this the rewrite can be expressed such that the semantics are preserved g _|_ = a or _|_ non-deterministically g' _|_ = a or _|_ non-deterministically Cheers! -Tyson