HaloO, John M. Dlugosz wrote:
This needs to be fleshed out. Decisions need to be made.
> Anyone want to discuss it with me?
I want to. But give me time. Meanwhile you could read e.g. <http://www.dcs.shef.ac.uk/~ajhs/classify/index.html>. This deals with F-bounded polymorphism in a tutorial style. A generalisation of that is Constraint Bounded Polymorphism as given in the papers of the WASP Group at <http://wasp.cs.washington.edu>. Another inspiration is the CDuce language <http://www.cduce.org> which is built around semantic subtyping. My point is that Perl 6 so far has defined a syntax for type markup but hardly defined how typing works ---I remember the "pain but no gain" thread. It might actually be the case that optional typing means that you need a module that implements it. I personally see types as the semantics of the code with the added benefit of being machine readable and thus can assist you in reasoning about the code. A type system is a tool just like an IDE allows you to browse the code, e.g. jumping to the definition of a class or all invocations of a method etc. There are two fundamental type errors in Perl 6: 1) a) no or b) ambiguous targets for dispatch 2) non-bindable args in non-dispatch position 1a and 2 can be easily avoided with slurpy Any protos. So the only remaining offender is 1b. And that might be pragmatized to just call them all. So we sort of end up with the impossibility of type errors :) Your concerns so far have been with the typing of assignment and binding. The former is easy because it involves the creation of a new value. Thus one can dispatch $x = $y on the container type of $x and the value type of $y and store the result in $x. So here you get an error of type 1 if any. Binding is more complicated because there is no new value involved but you want two containers to share a value. This is where Larry's view concept comes in to avoid the invariance problem of rw containers. OTOH the synopsis say that binding replaces the container, so my Int $x = 13; my Str $y = 'foo'; $y := $x; $y = 42; # OK, type of $y now Int but that contradicts the fact that binding happens when functions are called sub foo (Dog $d) { say $d; } my Int $x = 23; foo $x; # $d := $x makes type of $d Int and prints 23? Note also that binding is specced only for scalars so far. Not for elements of an array or hash! Regards, TSa. -- The Angel of Geometry and the Devil of Algebra fight for the soul of any mathematical being. -- Attributed to Hermann Weyl
