Controlling semantics of AND / OR operators

When using OPTIONS SHORT CIRCUIT at the beginning of a module, the runtime system will optimize the evaluation of boolean expressions involving AND and OR operators, by using the short-circuit evaluation method (also called minimal evaluation method). This behavior is enabled for the whole module.

By default, the behavior of AND and OR operators is to evaluate all operands on the left and right side of the operator. In fact this is not required: If the left operand of the AND evaluates to FALSE, there is no need to evaluate the right operand, because the result of the AND operator will be false, anyway. Similarly, when the left operand of an OR expression evaluates to TRUE, there is not need to evaluate the right operand, since the result of the boolean expression will be true, anyway.

This method can improve performances and simplify programming. However, existing code may rely on the fact that all parts of a boolean expression are evaluated, especially when calling functions that do some processing. By using the short-circuit evaluation method, it is unsure that the function used in the right operand of AND/OR will be called, because it depends on the result of the left operand.

By using short-circuit evaluation, it is possible to reference a dynamic array in the same boolean expression, after checking that the index is in the current array element range:

IF x<=arr.getLength() AND arr[x].order_date > TODAY THEN
     ...
END IF

With the default AND semantics, in this code, the right operand is also evaluated. If the x index is greater as the array length, new array elements will be automatically created in the expression on the right of the AND operator. To avoid this situation, you are forced to write following code, when OPTIONS SHORT CIRCUIT is not used:

IF x<=arr.getLength() THEN
  IF arr[x].order_date > TODAY THEN
      ...
  END IF
END IF