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# Expression

An expression is a combination of property operators and parameters. When an expression is evaluated sequentially in priority  order, all the operators are executed.

The result of that execution will be either a property or a parameter (in the case of single-parameter expression). Their value shall be called the value of the expression.

An expression can be described by the following set of recursive rules:

 Rule Description `expression := parameter | constant | prefixOperator` A single parameter, constant, or non-arithmetic prefix operator `expression := prefixArithmOp expression` A unary arithmetic prefix operator, with the expression passed to it as an operand `expression := expression postfixOp` A unary postfix operator, with the expression passed to it as an operand `expression := expression binaryOp expression` A binary operator with the expressions passed to it as operands `expression := ( expression )` Expression in parentheses

An expression cannot include context-independent property operators.

Examples

 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17``` ``` CLASS Team; wins(team) = DATA INTEGER(Team); ties(team) = DATA INTEGER(Team); points(Team team) = wins(team) * 3 + ties(team); // The number of points received by the team for the matches played // In this case, the expression is written to the right of the equal sign. It defines a new property called points. // When calculating the expression, two JOIN operators are first executed: wins(team) and ties(team), substituting the team parameter in the wins and ties properties // Then the multiplication operator will be executed, which will build a property that returns a number equal to the product of the return value of wins(team) and the number 3 // Then the addition operator will be executed, which will create a property that sums the return values (wins(team) * 3) and ties(team) // The resulting property will be the result of the expression CLASS Game; CLASS BonusGame : Game; gamePoints(Game game) = 2 (+) (1 IF game IS BonusGame); // The number of points per game. If the game is bonus, then 3, otherwise 2. // In this example, the order of execution of the operators will be as follows: IS, IF, (+) ```

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