Write regular expressions to match the following classes of Tiger tokens:

  a) Identifiers (i.e., variable names)
  b) Integer constants
  c) Comments (do _not_ try to handle comments-in-comments)

For one of them, you may use _only_ the fundamenal regular
expression constructors (epsilon, constants, concatentation,
disjunction (|), and closure (*)); for the other two, you
may use short-hands as well if you know them, such as character
classes ([]), positive closure (+), etc. If you don't know what
the heck I'm talking about, spend up to 20 minutes reviewing this
by reading Appel's book or the CS245 text.

Use Appendix A of Appel's book (available in the bookstore or the
library, or (I think) in the lab too) for reference on Tiger.