On Fri, Jan 14, 2011 at 6:17 PM, Robert Ramey <ramey@rrsd.com> wrote:
David Sankel wrote:
Thanks for your detailed response Robert...
<snip> To really do this right, I see the following as necessary
a) Clarify and simplify the current archive concept. I've thought about this alot and know what I want to do - but I'm not excited enough to do it.
I've been giving some thought to this. Not as much clarifying and simplifying, but more distilling the essence of the domain. I have a feeling that if we nail the essence down, all the compositionality will be there without having to tack it on as an afterthought.
Here's what I have so far:
concept Archive: struct _ where { typedef _ RState ; typedef _ WState
; template< typename T > struct lookup { typedef _ type // This _ is either mpl::void_ or // std::pair< function< void (RState&, const T&) > // , function< T (WState&) > // > ; type operator()() const; } };
Something fits the archive concept if they fill in the blanks above. RState and WState are state information required for reading and writing. The lookup type function, passed type T, will either return mpl::void_ or a pair. If it returns void_ we know that T is not considered a primitively serializable type. If it returns the pair, we know it is a serializable type witnessed by the pair of write and read functions returned by operator().
One key condition is that the primitive types for an Archive, if they are templates, must be *fully saturated*. Meaning that:
template<> lookup< std::vector<bool> >
is fine, but
template<typename T> lookup< std::vector<T> >
is not. This condition prevents recursive lookup calls with non-primitives. This, I think, is going to be the key to compositionality later. More to come...
Does all of this make sense so far?
In all honesty, I didn't understand even one sentence of the above.
Ah, darn. I have the terrible curse of thinking in a very precise and powerful language (denotational semantics with Agda as the semantic domain in this case), but find it terribly difficult to translate it to prose. For the record, here is what I'm trying to translate: μ [[concept Archive]] = data Archive : Set where archive : (RState,WState : Set) → (l : List ( T : Set , (RState,T) → IO RState , WState → IO (WState,T) )) → UniqueFsts l → Archive I'm going to think more about how to explain this and try again. Thanks for hanging in there. David -- David Sankel Sankel Software www.sankelsoftware.com