4.6 :`RegularExpressionParser` is broken

[xgillard]

Concerns : JaCoP 4.6 (Java 11).

I spotted a few issues in the code of the RegularExpressionParser class introduced in 4.6.

• (this one is fixed in the enclosed patched file) the class is unusable since the result of lexer.nextToken() is never used. As a consequence of that, any call to parse yields 'null'.
• The dot notation parsing is flaky. For instance, the following two examples relate toi the handling of epsilon expressions but are not orthogonal to one another.

// Prints "null.(32)*"
System.out.println(new PatchedRegexParser(new StringReader("(.32*)")).parse(false));

// Warns of a syntax error then prints "32.(null).*"
System.out.println(new PatchedRegexParser(new StringReader("(32.*)")).parse(false));

• In some cases (ie when a dot is missing) the parser silently drops a whole portion of the text to parse. For example, consider the following example:

// Prints "(17)*.23" and nothing more.
System.out.println(new PatchedRegexParser(new StringReader("(32.14*)17*.23")).parse(false));

Btw, I wonder if reusing the . and + symbols for summation and concatenation was judicious. Indeed, these symbols have different meaning in POSIX-style regexes (and I assume most people would expect that meaning)

PatchedRegexParser.java.txt