30  Pascal User Manual  Figure 4.c  Syntax diagram for  Variable  Figure 4.d  Syntax diagram for  Factor  Varllableldentifier  Coml~onentVariable  ~  IdenltifiedVariable  J  BufferVariable  I  SetConstructor  UnsignedConstant  J  Boundldentifier  I  Variable  J  Functionldentifier  l  ActualParameterList  f--'t  (  L  Expression  J  )  not  Factor  An  expression  is  a rule  for calculating a value based on  the  conventional rules of algebra for left-to-right evaluation of operators  and  operator precedence.  Expressions are composed of factors, terms,  and simple expressions.  Factors  are evaluated first and consist of individual constants or  variables or function designators or array-parameter bounds or set  constructors (see Chapter 8). A factor may also consist of the operator  not  applied to another factor representing a Boolean value. A factor  may also comprise an expression enclosed within parentheses which is  evaluated independently of preceding and following operators. 