Structuring a program
Ada

The main concept for structuring a program in Ada is the program unit. There are three such units: function, procedure and package. All these units are generally defined in two stages: the signature (known in Ada as the specification) and then the body, which repeats the signature, determines the "content" of the unit, and also contains a declarative part whose scope is limited to the unit. In the case of functions and procedures, the specification can be omitted.

Remember that other program units can be defined within the signature of these program units.