An expression is a compact notation for a combination of operations that go together to form a result.

It is convenient to include single variables, values, function calls and single operations as types of expressions. This simplifies defintions and descriptions. The reason is that all results in values or variables.


Expressions can be of the following types:

Special type of expression

  • Parenthesis (see below for more information)

Technically included as expressions for convenience


Parenthesis can be used to around a subexpression to ensure that this subexpression is evaluated as a whole before any further evaluation.

Parenthesis can also be used for increased readability.

Mixing expressions

Expressions of different types can be mixed together in a single expression. To nest an expression of one type in an expression of another type, the included expression must be enclosed in parenthesis.

Depending on the evaluation process

If a function is called in an expression then it is illegal to change the value of the input parameter. The reason is it creates a dependency on the evaluation process of the expression. Such dependencies are not allowed in the ProgsBase system.

T-Tables and T-Forms

T-Tables and T-Forms are useful for understanding expressions.

For more information about T-Tables and T-Forms, see T-Tables.