Identifiers

An identifier must have one of these forms:

• alphanumeric: any sequence of letters, digits, primes (') and underbars (_) starting with a letter or prime;
• symbolic: any non-empty sequence of the following symbols:
  ! % SPMamp; $ # + - / : < = > ? @   ` ^ | *;

In either case, however, reserved words are excluded. This means that for example # and | are not identifiers, but ## and |=| are identifiers.

There are six classes of identifiers:

• A type variable 'a is an alphanumeric identifier starting with a prime.
• A label lab is an identifier, or a positive integral numeral 1 2 3 ... not starting with 0.
• For each identifier class X marked `long' above there is a class longX of long identifiers, which may have a qualifier consisting of a unit identifier followed by a dot `.' :