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6.3 Subprogram Bodies
1
[A subprogram_body
specifies the execution of a subprogram.]
Syntax
2
subprogram_body
::=
subprogram_specification is
declarative_part
begin
handled_sequence_of_statements
end [
designator];
3
If a designator
appears at the end of a subprogram_body,
it shall repeat the defining_designator
of the subprogram_specification.
Legality Rules
4
[In contrast to other bodies,] a
subprogram_body
need not be 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.
{full conformance (required)} Static Semantics
5
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
6
{elaboration (non-generic subprogram_body)
[partial]} The elaboration of a non-generic
subprogram_body has no other effect
than to establish that the subprogram can from then on be called without
failing the Elaboration_Check.
6.a
Ramification: See 12.2
for elaboration of a generic body. Note that protected subprogram_bodies
never get elaborated; the elaboration of the containing protected_body
allows them to be called without failing the Elaboration_Check.
7
{execution (subprogram_body)
[partial]} [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
8
Example of procedure
body:
9
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;
10
Example of a function
body:
11
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;
Extensions to Ada 83
11.a
{extensions to Ada 83}
A renaming_declaration
may be used instead of a subprogram_body.
Wording Changes from Ada 83
11.b
The syntax rule for subprogram_body
now uses the syntactic category handled_sequence_of_statements.
11.c
The declarative_part
of a subprogram_body is now required;
that doesn't make any real difference, because a declarative_part
can be empty.
11.d
We have incorporated some rules
from RM83-6.5 here.
11.e
RM83 forgot to restrict the definition
of elaboration of a subprogram_body
to non-generics.
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