Re: How to implement dynamic typing?

George Neuner <gneuner2@comcast.net> wrote:
>
>At first glance it seems that having the descriptor together with the
>pointer saves time, extra fetching, cache pollution, etc. for
>"frequent" operations like bounds checking, object length/size
>retrieval, etc. But, in fact, studies of real programs have shown
>that descriptor accesses occur much less frequently than simple type
>checks, identity checks (comparing pointers), data accesses and object
>referrals (storing an object reference). Even in OO languages, method
>calls are less frequent than data accesses. YMMV, but most language
>implementors have decided that it is worthwhile to trade indirect
>descriptors for register-sized pointers.


LuaJIT takes an interesting approach. Its only numeric type is the
double precision floating point number. It uses different kinds of NAN
as tags for the other types, with the pointer embedded in the
mantissa.


http://article.gmane.org/gmane.comp.lang.lua.general/44823


Regarding typed word-sized pointers, see for instance
http://www.haskell.org/~simonmar/papers/ptr-tagging.pdf


Tony.
--
f.anthony.n.finch <dot@dotat.at> http://dotat.at/

Return to the comp.compilers page.
Search the comp.compilers archives again.