"Is the use of this type of pattern language something required to make hygienic macros work or is it just a design choice that the Scheme implementors made?"
Great minds wonder alike. Check out the "What's up with Scheme macros?" thread I kicked off on comp.lang.lisp. I do believe you will like I be sorry you asked. :)
I think somewhere in the dozens of treatises is the response "design choice", but I also think that response was challenged (surprise! surprise!). But I am just a working application programmer and I could not understand very much of what they were saying.
I did get a kick out of one shocked Schemer insisting something was trivial and then posting a twenty-line solution which at one point had a form beginning with four (!) left parens.
Pattern matching is completely orthogonal to hygiene.
You could add in another operator, %, that performs exactly the same as ` but hygienically.
Personally I'd settle for just being able embed procedures in code trees like you can in common lisp. Being able to write.
Hygienic macros do not require pattern-matching, as proven by the example of MIT scheme. Basically, macros in their system take three arguments - an s-expression, the environment the s-expression is being evaluated in, and the environment the macro is written in - and return syntax, which is an s-expression where you've chosen explicitly for each variable what environment it should be evaluated in. (More or less. If you're interested, it's called syntactic closures and you can probably find stuff about it online, or I can just write more here if people want.) I don't remember any way to insert a free identifier, but it might be there.
By the way, arc can already do half of that if you put (procedure? x) into literal.scm. The harder part is making variable references to things that aren't procedures, and I'm not quite sure how you'd do that (except the really annoying way, by wrapping everything in a procedure application).
SRFI-72 is another proof, as someone posted below, and might be better than syntactic closures (I don't know).
