4. Identifiers

For the purpose of this assignment, identifiers are simple. They must start with an alphabetical character. This character may be followed by numbers or alphabetical characters. A keyword cannot be used as an identifier.

Examples of valid identifiers:

hello
h
h3llo
Hi
h3

Examples of invalid identifier:

3d
a-bad-variable-name
no@twitter
we.don't.like.punctuation
or_spelling