Editing Ada (programming language) (section)

=== Packages, procedures and functions ===
Among the parts of an Ada program are packages, procedures and functions.

Functions differ from procedures in that they must return a value. Function calls cannot be used "as a statement", and their result must be assigned to a variable. However, since Ada 2012, functions are not required to be pure and may mutate their suitably declared parameters or the global state.<ref>{{cite web |title=Subprograms |url=https://learn.adacore.com/courses/intro-to-ada/chapters/subprograms.html#function-calls |website=learn.adacore.com |publisher=AdaCore |access-date=14 April 2024}}</ref>

Example:
Package specification (example.ads)
<syntaxhighlight lang="ada" line>
package Example is
     type Number is range 1 .. 11;
     procedure Print_and_Increment (j: in out Number);
end Example;
</syntaxhighlight>
Package body (example.adb)
<syntaxhighlight lang="ada" line>
with Ada.Text_IO;
package body Example is

  i : Number := Number'First;

  procedure Print_and_Increment (j: in out Number) is

    function Next (k: in Number) return Number is
    begin
      return k + 1;
    end Next;

  begin
    Ada.Text_IO.Put_Line ( "The total is: " & Number'Image(j) );
    j := Next (j);
  end Print_and_Increment;

-- package initialization executed when the package is elaborated
begin
  while i < Number'Last loop
    Print_and_Increment (i);
  end loop;
end Example;
</syntaxhighlight>
This program can be compiled, e.g., by using the freely available open-source compiler [[GNAT]], by executing
<syntaxhighlight lang="bash">gnatmake -z example.adb</syntaxhighlight>

Packages, procedures and functions can nest to any depth, and each can also be the logical outermost block.

Each package, procedure or function can have its own declarations of constants, types, variables, and other procedures, functions and packages, which can be declared in any order.