Variables

Variable =
     s-variable | t-variable | e-variable |
     v-variable.
s-variable = "s" [ "." ] VariableIndex.
t-variable = "t" [ "." ] VariableIndex.
v-variable = "v" [ "." ] VariableIndex.
e-variable = "e" [ "." ] VariableIndex.

VariableTypeDesignator = "s" | "t" | "v" | "e".
VariableIndex = IdentifierTail.

A variable consists of a variable type designator followed by a variable index. The type designator and the index may be separated by an optional dot. For example:

    tHead  eTail e.1 e1  tX s t e

Hence, eI and e.I represent the same variable.

Adjacent variables must be separated. For example, sAeB is a single variable, whereas sA eB is a sequence of two variables.

The index of a variable may be omitted, which means that the index is unique and different from the indices of all other variables appearing in the program. Thus, for example, if the variables e1000 and e2000 do not appear in the program, the sequence e e may be replaced with e1000 e2000.

Variables are distinguished into four classes: s-variables, t-variables, v-variables, and e-variables, the class of a variable being determined by the type designator.