On Thu, Jul 28, 2005 at 06:31:34PM +0200, "TSa (Thomas Sandla�)" wrote: > BTW, where can I read about PIL, other then in Parrot/Pugs svn?
(Cc'ing in P6C.) The current type-indexed design of PIL is going away, because it is closely tied to the PIR/Parrot model, to the disadvantage of our Perl5/JavaScript backends. Also it does not capture any notion of rank-n types, and relies on the VM for a semantics for container types, which is prone to trouble. In the past few weeks I've been reading up on F<:, Fw, CoC, vObj, as well as intersectional and split types for object calculi, in the hope of revamping PIL -- Pugs's new internal language -- that can alleviate backend author's pain and improve type-directed translation. Perl 6's uniqueness is that it relies on runtime-rebindable package objects for its type system, but at the same time carries the vague promise of partial static analysis for the part of the closed world via toplevel `use optimize`. The semantic of type annotations remains unresolved; I reflected this in the recent `the meaning of "returns"` thread. It would be far easier if we concede that Perl 6 is essentially untyped, and all type annotations are merely storage hints, that will still always require runtime coercion. This coincide with Parrot's current idea of never checking subroutine parameter's PMC types (except for MMD), and always resolve method calls as late as possible, exactly as Perl 5 did. Under that view, the only use of type annotation at compile time is speeding up property/method lookup for typed variables, so they can be looked up by number instead of names, provided new fields always go toward the end. Other than that, they can only serve as runtime assertions, leading to the curious effect that well-typed programs can run slower than the unannotated counterpart. However, my intuition is that a soft-typed system, with clearly defined dynamic parts translated to runtime coerce and dependent types, that can work exactly as Perl 5 did at first, but provide sensible inferencing and compile-time diagnostics as you gradually provide annotations, is really the way forward. Under soft typing, Parrot's role would become a fast implementation for the object space and primitives, but the soundness of large-scale programs and the standard library will be provided by the compiler, not the runtime. This plays well with Pugs's -- not neccessarily Perl 6's -- goal of keeping the language retargettable. This may not be popular view, as evidented by the relative lack of research and real-world interest to bridge the gap of static/dynamic languages, so it would take a while to come up with a suitable formal treatment. I'm currently trying to express this idea under the F<: framework for the new PIL, and I'll keep p6c posted as it goes forward, and cotinue to reflect design issues to p6l. Thanks, /Autrijus/
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