Real Expressions

To facilitate the definition of interdependent quantities, any real value can be entered as an arithmetic expression. When a value used in an expression is redefined by the user or changed in a matching process, the expression is re-evaluated. Expression definitions may be entered in any order. MAD evaluates them in the correct order before it performs any computation. At evaluation time all operands used must have values assigned. A real expression can occur in real arrays.

A real expression is built from operators and operands:

real-ref  ::= real-variable |
              real-array "[" index "]" |
              object "->" real-attribute |
              object "->" real-array-attribute "[" index "]" |

table-ref ::= table "@" place "->" column-name

primary   ::= literal-constant |
              symbolic-constant |
              "#" |
              real-ref |
              table-ref |
              function-name "(" arguments ")" |
              (real-expression)

factor    ::= primary |
              factor "^" primary

term      ::= factor |
              term "*" factor |
              term "/" factor

real-expr ::= term |
              "+" term |
              "-" term |
              real-expr "+" term |
              real-expr "-" term |

It may contain functions, Parentheses indicate operator precedence if required. Constant sub-expressions are evaluated immediately, and the result is stored as a constant.