SIMPOL Documentation

There are four pre-defined values in SIMPOL, two of which can be applied to to every type, and two that are specific to the boolean type. These values are: .true, .false, .nul, and .inf. The first two have been discussed in the section on the boolean type. The latter two can be applied to all value types and .nul can be applied to all types, both value and object types. The value .inf stands for infinity. It has many similarities to the .nul value and in some cases it is converted to that value if there is no available value to represent infinity, such as in SQL. The infinity that is represented in SIMPOL is both positive and negative infinity, but there is no value that represents infinitesimal (1 divided by infinity). In fact, in SIMPOL 1 / .inf is equal to .nul.

It is important to understand how the two special values, .nul and .inf are used within SIMPOL and how their very existence in the language plays a role in how programs written in it may or may not work as expected. The first of the two values, .nul is used in many places as a return value and also it is the default value of a variable that has been created but not yet been initialized with a value. Having the concept of a null value in the programming language is quite useful, especially when interacting with databases where the desire to retain the characteristic of an empty field within a calculation may be desirable. The null value in SIMPOL follows some fairly clear rules. The value .nul combined with any other value or values results in the value .nul. If in your program you are suddenly finding an unexpected null result, then chances are that somewhere a value was uninitialized (or a database field is empty).