Identifiers

identifier ::= upper-identifier |
               lower-identifier |
               discard-identifier

upper-identifier ::= [A-Z] [0-9a-zA-Z]*

lower-identifier ::= [a-z] [_0-9a-z]*

discard-identifier ::= '_' [_0-9a-z]*

binding-identifier ::= discard-identifier |
                       code-identifier

code-identifier ::= lower-identifier |
                    type-keyword