This package uses Jay Earley's algorithm for parsing context free grammars, and
comes with some generic Abstract Syntax Tree routines. There is also a prototype
scanner which does its job by combining Python regular expressions.

(SPARK stands for Scanning, Parsing, and Rewriting Kit. It is a poor name since
it conflicts with a more popular package of the same name. In the future we will
rename this.)

The original version of this was written by John Aycock for his Ph.D thesis and
was described in his 1998 paper: "Compiling Little Languages in Python" at the
7th International Python Conference. The current incarnation of this code is
maintained (or not) by Rocky Bernstein.

Note: Earley algorithm parsers are almost linear when given an LR grammar. These
are grammars which are left-recursive.