Ada Reference Manual (Ada 2022) — Legal Information

6.3 Subprogram Bodies

A subprogram_body specifies the execution of a subprogram.

Syntax

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subprogram_body ::=
    [overriding_indicator]
    subprogram_specification
       [aspect_specification] is
       declarative_part
    begin
        handled_sequence_of_statements
    end [designator];

If a designator appears at the end of a subprogram_body, it shall repeat the defining_designator of the subprogram_specification.

Legality Rules

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In contrast to other bodies, a subprogram_body is allowed to be defined without it being the completion of a previous declaration, in which case the body declares the subprogram. If the body is a completion, it shall be the completion of a subprogram_declaration or generic_subprogram_declaration. The profile of a subprogram_body that completes a declaration shall conform fully to that of the declaration.

Static Semantics

A subprogram_body is considered a declaration. It can either complete a previous declaration, or itself be the initial declaration of the subprogram.

Dynamic Semantics

The elaboration of a nongeneric subprogram_body has no other effect than to establish that the subprogram can from then on be called without failing the Elaboration_Check.

The execution of a subprogram_body is invoked by a subprogram call. For this execution the declarative_part is elaborated, and the handled_sequence_of_statements is then executed.

Examples

Example of procedure body:

procedure Push(E : in Element_Type; S : in out Stack) is
begin
   if S.Index = S.Size then
      raise Stack_Overflow;
   else
      S.Index := S.Index + 1;
      S.Space(S.Index) := E;
   end if;
end Push;

Example of a function body:

function Dot_Product(Left, Right : Vector) return Real is
   Sum : Real := 0.0;
begin
   Check(Left'First = Right'First and Left'Last = Right'Last);
   for J in Left'Range loop
      Sum := Sum + Left(J)*Right(J);
   end loop;
   return Sum;
end Dot_Product;

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