The lexer uses JLex by Elliot Berk to create {@link metropolis.metamodel.frontend.lexer.Lexer}.
JLex can be found at http://www.cs.princeton.edu/~appel/modern/java/JLex/
http://www.cs.princeton.edu/~appel/modern/java/JLex/
We use a local copy in $METRO/src/com/JLex.
$METRO/src/com/JLex