Unexpected exception encountered. Regex is "\/\*[{white}|.]*\*\/" about jflex HOT 3 OPEN

Attached is the full jflex file.

from jflex.

minijava.jflex.txt

GitHub only accepts files with certain extension. I've added .txt.

from jflex.

This does indeed look like a bug, thanks for reporting it. But it's mostly a bug in error reporting (sorry :-)). Enabling the use of macros in character classes like [..] seems to have uncovered a whole bunch of combinations that aren't properly rejected.

In this case, {white} is a full regular expression (.. | ..), not itself a character class, so it can't be used inside the [..].

For fixing your specific problem, it looks like you might be wanting just ({white}|.) instead of [{white}|.]. That said, this is equivalent to just [^] (any character, including newline).

On the danger of doing your homework for you, there is a pitfall with this: "/*" [^]* "*/" will not quite match a slash-star comment. E.g. it will match all of /* abc */ return x; /* abc */ in one go, because JFlex will always give you the longest possible match.

The expression you'd need is "/*" followed by any string that is not "*/", followed by "*/". There is a special operator for this in JFlex (not present in usual regexp engines). You can write: "/*" ~"*/"

from jflex.