From: Vidar Hokstad <vidar@...>
Date: 2006-09-04T18:40:14+09:00
Subject: Re: Joel Spolsky on languages for web programming


Devin Mullins wrote:
> David Vallner wrote:
> > Speaking purely theorethically, Ruby can not be made as performant as
> > Java or C# could be made if they had ideally performing implementations.
> > Latent typing makes it almost impossible to do certain optimizations as
> > static typing does. That's pure fact.
> Irrelevant. In many cases, the fact that Ruby has latent typing is an
> *implementation detail*. Ruby has *no type declarations*, but in many
> cases static type inference can be applied to get the same optimizations
> of which Java and C# implementations avail themselves. (Disclaimer:
> that's about as much as I know about this subject.)

You're absolutely right.

Look to Haskell for  a good example a _statically typed_ language
almost free of type annotation of any kind - type information is almost
exclusively added by the compiler (though you can add type
annotations).

While Ruby has features that make it impossible for an implementation
to use strict static typing everywhere, a lot of a typical Ruby
application could be statically typed by an implementation using type
inference fairly easily by doing some relatively simple flow analysis
combined with marking up the parse tree.

Doing it for a pure interpreter would be easy, but the advantages would
be relatively limited. Doing it for a JIT compiler would also be quite
straightforwards and does have the potential of very significant
speedups.

For a full fledged compiler it would be tricky without some
restrictions - the main problem is Ruby's introspective features and
various eval mechanisms, which means the type inference valid at
compile time might not hold at runtime. Add a few restrictions on the
use of load/require etc. and the use of eval's and/or some way of
adding some basic type annotation to guide the compiler for "extension
points" (classes/methods that will be affected by runtime changes) and
it would be doable without significant changes.

Vidar