Hi Dave, first, my compliments on your lambda proposal. This should significantly simplify the core language after expanding sugars -- especially if you succeed at redefining function as desugaring to lambdas. That would be awesome!
On Sat, Oct 11, 2008 at 5:34 AM, David Herman <[EMAIL PROTECTED]> wrote: > Here's roughly the semantics of return-to-label: > > - return-to-label first checks to see if the label is live on the stack > - if not, it raises an exception from the point where the return was attempted > - but if so, it attempts to unwind the stack to the point where the label was > executed, passing through any intervening finally clauses > - if any of the finally clauses has its own non-local exit, this interrupts > and aborts the unwinding > > Thank you for pointing out, though, that try/catch isn't so easily defined on > top of return-to-label, since it still needs special handling for finally. > The options are either to define a lower-level primitive underlying > try/finally (akin to Scheme's dynamic-wind), or to leave exceptions -- or at > least try/finally -- as primitive. I lean towards the latter; dynamic-wind is > a subtle beast. > > [For those interested in dynamic-wind, Flatt et al's ICFP 07 paper has a nice > investigation into its semantics: > http://www.cs.utah.edu/plt/publications/icfp07-fyff.pdf] I haven't looked at the Flatt paper yet. But the semantics you explain above corresponds exactly to E's escape expressions. And E also treats try/finally primitive for similar reasons. (Historical note: The E escape construct and the call/ec previously explained both originate in an "escape" statement by Reynolds from a paper in the late 60s or early 70s. I don't recall whether Reynolds had any mechanism analogous to try/finally.) -- Cheers, --MarkM _______________________________________________ Es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
