[Evolution] boolean searches - expressions

[Thomas Frayne <tomf sjpc org>]

Periodically, users request a capability for boolean searches in
Evolution.  The response is usually: we won't implement it, because you
can do the same thing with expressions.

The next question is: Where is the syntax for expressions documented? 
And the answer is: Nowhere but in the source code.  However,
http://www.ximian.com/support/manuals/evolution_10/usage-mail-organize-vfolders.html
states: Expression - For programmers only: match a message according to
an expression you write in the Scheme language, used to define vFolders
in Ximian Evolution

I have seen documentation of the Scheme language:
http://www.swiss.ai.mit.edu/~jaffer/r5rs_toc.html
describes Scheme.

http://www.cs.utexas.edu/users/wilson/schintro/schintro_toc.html
has a Scheme tutorial.

It would be helpful to have a few examples of Scheme expressions which
can be used in a vfolder definition, with a descriptions of what they
find.  Failing that, where are expressions implemented in the Evolution
source?

I think that requiring Gnome Desktop users to know programming in a
little known language is not the way to attract users of Microsoft
Windows to Linux. At least, regular expressions should be allowed.  Far
better would be to allow adding AND, OR, NOT after each criterion so
that unsophisticated users can easily construct flexible searches.