1.1.2 Structure
1
This International Standard contains thirteen sections,
fourteen annexes, and an index.
2
{core
language} The
core of the Ada language
consists of:
3
4
5
6
7
{Specialized
Needs Annexes} {Annex
(Specialized Needs)} {application
areas} The following
Specialized Needs
Annexes define features that are needed by certain application areas:
8
9
10
11
12
13
14
{normative}
{Annex (normative)}
The core language and the Specialized Needs Annexes
are normative, except that the material in each of the items listed below
is informative:
15
- Text under a NOTES or Examples heading.
16
- Each clause or subclause whose title
starts with the word “Example” or “Examples”.
17
All implementations shall conform to the core language.
In addition, an implementation may conform separately to one or more
Specialized Needs Annexes.
18
{informative}
{non-normative: See
informative} {Annex
(informative)} The following Annexes are
informative:
19
20
21
22
23
23.a
Discussion: The idea of the Specialized
Needs Annexes is that implementations can choose to target certain application
areas. For example, an implementation specifically targeted to embedded
machines might support the application-specific features for Real-time
Systems, but not the application-specific features for Information Systems.
23.b
The Specialized Needs Annexes extend the core
language only in ways that users, implementations, and standards bodies
are allowed to extend the language; for example, via additional library
units, attributes, representation items (see
13.1),
pragmas, and constraints on semantic details
that are left unspecified by the core language. Many implementations
already provide much of the functionality defined by Specialized Needs
Annexes; our goal is to increase uniformity among implementations by
defining standard ways of providing the functionality.
23.c/2
{
AI95-00114-01}
We recommend that the
certification validation
procedures allow implementations to
certify validate
the core language, plus any set of the Specialized Needs Annexes. We
recommend that implementations
not be allowed to
certify validate
a portion of one of the Specialized Needs Annexes, although implementations
can, of course, provide
uncertified unvalidated
support for such portions. We have designed the Specialized Needs Annexes
assuming that this recommendation is followed. Thus, our decisions about
what to include and what not to include in those annexes are based on
the assumption that each annex is
certified validated
in an “all-or-nothing” manner.
23.d
An implementation may, of course, support extensions
that are different from (but possibly related to) those defined by one
of the Specialized Needs Annexes. We recommend that, where appropriate,
implementations do this by adding library units that are children of
existing language-defined library packages.
23.e
An implementation should not provide extensions
that conflict with those defined in the Specialized Needs Annexes, in
the following sense: Suppose an implementation supports a certain error-free
program that uses only functionality defined in the core and in the Specialized
Needs Annexes. The implementation should ensure that that program will
still be error free in some possible full implementation of all of the
Specialized Needs Annexes, and that the semantics of the program will
not change. For example, an implementation should not provide a package
with the same name as one defined in one of the Specialized Needs Annexes,
but that behaves differently, even if that implementation does not
claim conformance to that Annex.
23.f
Note that the Specialized Needs Annexes do not
conflict with each other; it is the intent that a single implementation
can conform to all of them.
24
Each section is divided into clauses and subclauses
that have a common structure. Each section, clause, and subclause first
introduces its subject. After the introductory text, text is labeled
with the following headings:
Language Design Principles
24.a
These are not rules of the language, but guiding
principles or goals used in defining the rules of the language. In some
cases, the goal is only partially met; such cases are explained.
24.b/2
This is not part of the definition of the language,
and does not appear in the Ada 2005 RM RM95.
Syntax
25
{syntax (under
Syntax heading)} {grammar
(under Syntax heading)} {context
free grammar (under Syntax heading)} {BNF
(Backus-Naur Form) (under Syntax heading)} {Backus-Naur
Form (BNF) (under Syntax heading)} Syntax
rules (indented).
Name Resolution Rules
26
{name resolution
rules} {overloading
rules} {resolution
rules} Compile-time rules that are used
in name resolution, including overload resolution.
26.a
Discussion: These rules are observed
at compile time. (We say “observed” rather than “checked,”
because these rules are not individually checked. They are really just
part of the Legality Rules in Section 8 that require exactly one interpretation
of each constituent of a complete context.) The only rules used in overload
resolution are the Syntax Rules and the Name Resolution Rules.
26.b
When dealing with non-overloadable declarations
it sometimes makes no semantic difference whether a given rule is a Name
Resolution Rule or a Legality Rule, and it is sometimes difficult to
decide which it should be. We generally make a given rule a Name Resolution
Rule only if it has to be. For example, “The name,
if any, in a raise_statement shall be the
name of an exception.” is under “Legality
Rules.”
Legality Rules
27
{legality rules}
{compile-time error}
{error (compile-time)}
Rules that are enforced at compile time.
{legal
(construct)} {illegal
(construct)} A construct is
legal
if it obeys all of the Legality Rules.
27.a
Discussion: These rules are not used
in overload resolution.
27.b
Note that run-time errors are always attached
to exceptions; for example, it is not “illegal” to divide
by zero, it just raises an exception.
Static Semantics
28
{static semantics}
{compile-time semantics}
A definition of the compile-time effect of each construct.
28.a
Discussion: The most important compile-time
effects represent the effects on the symbol table associated with declarations
(implicit or explicit). In addition, we use this heading as a bit of
a grab bag for equivalences, package specifications, etc. For example,
this is where we put statements like so-and-so is equivalent to such-and-such.
(We ought to try to really mean it when we say such things!) Similarly,
statements about magically-generated implicit declarations go here. These
rules are generally written as statements of fact about the semantics,
rather than as a you-shall-do-such-and-such sort of thing.
Post-Compilation Rules
29
{post-compilation
error} {post-compilation
rules} {link-time
error: See post-compilation error} {error
(link-time)} Rules that are enforced before
running a partition.
{legal (partition)}
{illegal (partition)}
A partition is legal if its compilation units are
legal and it obeys all of the Post-Compilation Rules.
29.a
Discussion: It is not specified exactly
when these rules are checked, so long as they are checked for any given
partition before that partition starts running. An implementation may
choose to check some such rules at compile time, and reject compilation_units
accordingly. Alternatively, an implementation may check such rules when
the partition is created (usually known as “link time”),
or when the partition is mapped to a particular piece of hardware (but
before the partition starts running).
Dynamic Semantics
30
{dynamic semantics}
{run-time semantics}
{run-time error}
{error (run-time)}
A definition of the run-time effect of each construct.
30.a
Discussion: This heading describes what
happens at run time. Run-time checks, which raise exceptions upon failure,
are described here. Each item that involves a run-time check is marked
with the name of the check — these are the same check names that
are used in a pragma Suppress. Principle:
Every check should have a name, usable in a pragma
Suppress.
Bounded (Run-Time) Errors
31
{bounded error}
Situations that result in bounded
(run-time) errors (see
1.1.5).
31.a
Discussion: The “bounds”
of each such error are described here — that is, we characterize
the set of all possible behaviors that can result from a bounded error
occurring at run time.
Erroneous Execution
32
{erroneous execution}
Situations that result in erroneous
execution (see
1.1.5).
Implementation Requirements
33
{implementation requirements}
Additional requirements for conforming implementations.
33.a
Discussion: ...as opposed to rules imposed
on the programmer. An example might be, “The smallest representable
duration, Duration'Small, shall not be greater than twenty milliseconds.”
33.b
It's really just an issue of how the rule is
worded. We could write the same rule as “The smallest representable
duration is an implementation-defined value less than or equal to 20
milliseconds” and then it would be under “Static Semantics.”
Documentation Requirements
34
{documentation requirements}
Documentation requirements for conforming implementations.
34.a
Discussion: These requirements are beyond
those that are implicitly specified by the phrase “implementation
defined”. The latter require documentation as well, but we don't
repeat these cases under this heading. Usually this heading is used for
when the description of the documentation requirement is longer and does
not correspond directly to one, narrow normative sentence.
Metrics
35
{metrics}
Metrics that are specified for the time/space properties
of the execution of certain language constructs.
Implementation Permissions
36
{implementation permissions}
Additional permissions given to the implementer.
36.a
Discussion: For example, “The implementation
is allowed to impose further restrictions on the record aggregates allowed
in code statements.” When there are restrictions on the permission,
those restrictions are given here also. For example, “An implementation
is allowed to restrict the kinds of subprograms that are allowed to be
main subprograms. However, it shall support at least parameterless procedures.”
— we don't split this up between here and “Implementation
Requirements.”
Implementation Advice
37
{implementation advice}
{advice}
Optional advice given to the implementer. The word
“should” is used to indicate that the advice is a recommendation,
not a requirement. It is implementation defined whether or not a given
recommendation is obeyed.
37.a/2
Implementation defined: Whether or not
each recommendation given in Implementation Advice is followed
— see M.3, “Implementation
Advice” for a listing.
37.b/1
Discussion: The advice generally shows
the intended implementation, but the implementer is free to ignore it.
The implementer is the sole arbiter of whether or not the advice has
been obeyed, if not, whether the reason is a good one, and whether the
required documentation is sufficient.
{ACVC
(Ada Compiler Validation Capability) [partial]} {Ada
Compiler Validation Capability (ACVC) [partial]} It
would be wrong for the
ACATS ACVC
to enforce any of this advice.
37.c
For example, “Whenever possible, the implementation
should choose a value no greater than fifty microseconds for the smallest
representable duration, Duration'Small.”
37.d
We use this heading, for example, when the rule
is so low level or implementation-oriented as to be untestable. We also
use this heading when we wish to encourage implementations to behave
in a certain way in most cases, but we do not wish to burden implementations
by requiring the behavior.
38
1
{notes}
Notes emphasize consequences of the rules described
in the (sub)clause or elsewhere. This material is informative.
Examples
39
Examples illustrate the possible forms of the constructs
described. This material is informative.
39.a
Discussion:
The next three headings list all language changes between Ada 83 and
Ada 95. Language changes are any change that changes the set of text
strings that are legal Ada programs, or changes the meaning of any legal
program. Wording changes, such as changes in terminology, are not language
changes. Each language change falls into one of the following three categories:
Inconsistencies With Ada 83
39.b
{
inconsistencies with Ada 83}
This
heading lists all of the upward inconsistencies between Ada 83 and Ada
95. Upward inconsistencies are situations in which a legal Ada 83 program
is a legal Ada 95 program with different semantics. This type of upward
incompatibility is the worst type for users, so we only tolerate it in
rare situations.
39.c
(Note that the semantics of a program is not
the same thing as the behavior of the program. Because of Ada's indeterminacy,
the “semantics” of a given feature describes a set
of behaviors that can be exhibited by that feature. The set can contain
more than one allowed behavior. Thus, when we ask whether the semantics
changes, we are asking whether the set of behaviors changes.)
39.d/2
This is not part of the definition of the language,
and does not appear in the Ada 95 or Ada 2005 RM RM95.
Incompatibilities With Ada 83
39.e
{
incompatibilities with Ada 83}
This
heading lists all of the upward incompatibilities between Ada 83 and
Ada 95, except for the ones listed under “Inconsistencies With
Ada 83” above. These are the situations in which a legal Ada 83
program is illegal in Ada 95. We do not generally consider a change that
turns erroneous execution into an exception, or into an illegality, to
be upwardly incompatible.
39.f/2
This is not part of the definition of the language,
and does not appear in the Ada 95 or Ada 2005 RM RM95.
Extensions to Ada 83
39.g
{
extensions to Ada 83}
This
heading is used to list all upward compatible language changes; that
is, language extensions. These are the situations in which a legal Ada
95 program is not a legal Ada 83 program. The vast majority of language
changes fall into this category.
39.h/2
This is not part of the definition of the language,
and does not appear in the Ada 95 or Ada 2005 RM RM95.
39.i
As explained above, the next heading does not represent any language
change:
Wording Changes from Ada 83
39.j/2
{
wording changes from Ada 83}
This
heading lists some of the non-semantic changes between
the
Ada 83 RM RM83 and the
the
Ada 95 RM RM95. It is incomplete;
we have not attempted to list all wording changes, but only the “interesting”
ones.
39.k/2
This is not part of the definition of the language,
and does not appear in the Ada 95 or Ada 2005 RM RM95.
39.l/2
Discussion:
The next three headings list all language changes between Ada 95 and
Ada 2005 (the language defined by the Ada 95 standard plus Technical
Corrigendum 1 plus Amendment 1). Each language change falls into one
of the following three categories:
Inconsistencies With Ada 95
39.m/2
{inconsistencies with
Ada 95} This heading lists all of the upward
inconsistencies between Ada 95 and Ada 2005. Upward inconsistencies are
situations in which a legal Ada 95 program is a legal Ada 2005 program
with different semantics.
39.n/2
Inconsistencies marked
with Corrigendum:{Corrigendum} are
corrections to the original Ada 95 definition introduced by Corrigendum
1. Inconsistencies marked with Amendment Correction:{Amendment
Correction} are corrections to the original
Ada 95 definition added by Amendment 1. Formally, these are inconsistencies
caused by Ada Issues classified as Binding Interpretations; implementations
of Ada 95 are supposed to follow these corrections, not the original
flawed language definition. Thus, these strictly speaking are not inconsistencies
between Ada 95 and Ada 2005. Practically, however, they very well may
be, as early Ada 95 implementations may not follow the recommendation.
Inconsistencies so marked are not portable between Ada 95 implementations,
while usually Ada 2005 will have more clearly defined behavior. Therefore,
we document these for completeness.
39.o/2
This is not part of the
definition of the language, and does not appear in the Ada 2005 RM.
Incompatibilities With Ada 95
39.p/2
{incompatibilities
with Ada 95} This heading lists all of the upward
incompatibilities between Ada 95 and Ada 2005, except for the ones listed
under “Inconsistencies With Ada 95” above. These are the
situations in which a legal Ada 95 program is illegal in Ada 2005.
39.q/2
As with inconsistencies,
incompatibilities marked with Corrigendum: are corrections to
the original Ada 95 definition introduced by Corrigendum 1. Incompatibilities
marked with Amendment Correction: are corrections to the original
Ada 95 definition added by Amendment 1. Formally, these are incompatibilities
caused by Ada Issues classified as Binding Interpretations; implementations
of Ada 95 are supposed to follow these corrections, not the original
flawed language definition. Thus, these strictly speaking are not incompatibilities
between Ada 95 and Ada 2005. Practically, however, they very well may
be, as early Ada 95 implementations may not follow the recommendation.
Therefore, some Ada 95 implementations may be able to compile the examples,
while others may not. In constrast, Ada 2005 compilers will have consistent
behavior. Therefore, we document these for completeness.
39.r/2
This is not part of the
definition of the language, and does not appear in the Ada 2005 RM.
Extensions to Ada 95
39.s/2
{extensions to Ada
95} This heading is used to list all upward compatible
language changes; that is, language extensions. These are the situations
in which a legal Ada 2005 program is not a legal Ada 95 program. The
vast majority of language changes fall into this category.
39.t/2
As with incompatibilities,
extensions marked with Corrigendum: are corrections to the original
Ada 95 definition introduced by Corrigendum 1. Extensions marked with
Amendment Correction: are corrections to the original Ada 95 definition
added by Amendment 1. Formally, these are extensions allowed by Ada Issues
classified as Binding Interpretations. As corrections, implementations
of Ada 95 are allowed to implement these extensions. Thus, these strictly
speaking are not extensions of Ada 95; they're part of Ada 95. Practically,
however, they very well may be extensions, as early Ada 95 implementations
may not implement the extension. Therefore, some Ada 95 implementations
may be able to compile the examples, while others may not. In constrast,
Ada 2005 compilers will always support the extensions. Therefore, we
document these for completeness.
39.u/2
This is not part of the
definition of the language, and does not appear in the Ada 2005 RM.
39.v/2
As explained above, the next heading does not represent any language
change:
Wording Changes from Ada 95
39.w/2
{wording changes from
Ada 95} This heading lists some of the non-semantic
changes between the Ada 95 RM and the Ada 2005 RM. This heading lists
only “interesting” changes (for instance, editorial corrections
are not listed). Changes which come from Technical Corrigendum 1 are
marked Corrigendum; unmarked changes come from Amendment 1.
39.x/2
This is not part of the
definition of the language, and does not appear in the Ada 2005 RM.
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