Marshall wrote: > David Hopwood wrote: >>Marshall wrote: >>>David Hopwood wrote: >>>>Marshall wrote: >>>> >>>>>The real question is, are there some programs that we >>>>>can't write *at all* in a statically typed language, because >>>>>they'll *never* be typable? >>>> >>>>In a statically typed language that has a "dynamic" type, all >>>>dynamically typed programs are straightforwardly expressible. >>> >>>So, how does this "dynamic" type work? >> >><http://citeseer.ist.psu.edu/abadi89dynamic.html> >> >>>It can't simply be the "any" type, because that type has no/few >>>functions defined on it. >> >>It isn't. From the abstract of the above paper: >> >> [...] even in statically typed languages, there is often the need to >> deal with data whose type cannot be determined at compile time. To handle >> such situations safely, we propose to add a type Dynamic whose values are >> pairs of a value v and a type tag T where v has the type denoted by T. >> Instances of Dynamic are built with an explicit tagging construct and >> inspected with a type safe typecase construct. > > Well, all this says is that the type "dynamic" is a way to explicitly > indicate the inclusion of rtti. But that doesn't address my objection; > if a typesafe typecase construct is required, it's not like using > a dynamic language. They don't require typecase to inspect values > before one can, say, invoke a function.
I was answering the question posed above: "are there some programs that we can't write *at all* in a statically typed language...?" >>"Gradual typing" as described in >><http://www.cs.rice.edu/~jgs3847/pubs/pubs/2006/siek06:_gradual.pdf> is >>another alternative. The difference between gradual typing and a >>"dynamic" type is one of convenience rather than expressiveness -- >>gradual typing does not require explicit tagging and typecase constructs. > > Perhaps this is the one I should read; it sounds closer to what I'm > talking about. Right; convenience is obviously important, as well as expressiveness. -- David Hopwood <[EMAIL PROTECTED]> -- http://mail.python.org/mailman/listinfo/python-list
