[m-rev.] for review: string switches using tries

[Zoltan Somogyi]

On Tue, 24 Feb 2015 18:04:51 +1100, Paul Bone <paul at bone.id.au> wrote:
> > string.m presents an encoding agnostic interface.  The implementation
> > only allows UTF-8 for the C/Erlang backends, and UTF-16 for the Java/C#
> > backends.
> 
> Is it possible to use the target's encoding method when creating the trie?

Yes, provided it is known. With --cross-compiling and --target=c, you
wouldn't know whether the target uses ASCII/utf8 or EBCDIC.
(As we just discussed, --cross-compiling does not specify anything useful
about the actual target platform.)

> I've been considering re-writing the streams library making Mercury always
> use one specific encoding, say UTF-8.  Then adding other encodings including
> the host system's default encoding as a wrappers that take one stream type
> and returns a new stream type.

That is a separate use case, one which can afford the cost of representation
conversions because it is already paying the cost of I/O. Switches don't have
that luxury. Tries have at most a minor performance advantage over hash switches.
If they can be made to work in a set of circumstances only by methods that
add enough overhead to make tries uncompetitive, then there is no point
in using those methods, even if they work.

Zoltan.