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<H1> 6.1 Subprogram Declarations</H1>
<DIV Class="Paranum"><FONT SIZE=-2>1</FONT></DIV>
<DIV Class="Normal"> [A <FONT FACE="Arial, Helvetica">subprogram_declaration</FONT>
declares a procedure or function.] </DIV>
<H4 ALIGN=CENTER>Syntax</H4>
<DIV Class="Paranum"><FONT SIZE=-2>2</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">subprogram_declaration<A NAME="I3004"></A>
::= </FONT><A NAME="I3005"></A><FONT FACE="Arial, Helvetica">subprogram_specification</FONT>;</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>3</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">abstract_subprogram_declaration<A NAME="I3006"></A>
::= </FONT><A NAME="I3007"></A><FONT FACE="Arial, Helvetica">subprogram_specification</FONT> <B>is</B> <B>abstract</B>;</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>4</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">subprogram_specification<A NAME="I3008"></A>
::= </FONT><BR>
<B>procedure</B> <A NAME="I3009"></A><FONT FACE="Arial, Helvetica">defining_program_unit_name</FONT> <A NAME="I3010"></A><FONT FACE="Arial, Helvetica">parameter_profile</FONT><BR>
| <B>function</B> <A NAME="I3011"></A><FONT FACE="Arial, Helvetica">defining_designator</FONT> <A NAME="I3012"></A><FONT FACE="Arial, Helvetica">parameter_and_result_profile</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>5</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">designator<A NAME="I3013"></A>
::= </FONT>[<A NAME="I3014"></A><FONT FACE="Arial, Helvetica">parent_unit_name</FONT> . ]<A NAME="I3015"></A><FONT FACE="Arial, Helvetica">identifier</FONT> | <A NAME="I3016"></A><FONT FACE="Arial, Helvetica">operator_symbol</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>6</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">defining_designator<A NAME="I3017"></A>
::= </FONT><A NAME="I3018"></A><FONT FACE="Arial, Helvetica">defining_program_unit_name</FONT> | <A NAME="I3019"></A><FONT FACE="Arial, Helvetica">defining_operator_symbol</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>7</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">defining_program_unit_name<A NAME="I3020"></A>
::= </FONT>[<A NAME="I3021"></A><FONT FACE="Arial, Helvetica">parent_unit_name</FONT> . ]<A NAME="I3022"></A><FONT FACE="Arial, Helvetica">defining_identifier</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>8</FONT></DIV>
<DIV Class="SyntaxIndented">[The optional <FONT FACE="Arial, Helvetica">parent_unit_name</FONT>
is only allowed for library units (see <A HREF="AA-10-1-1.html">10.1.1</A>).]
</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>9</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">operator_symbol<A NAME="I3023"></A>
::= </FONT><A NAME="I3024"></A><FONT FACE="Arial, Helvetica">string_literal</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>10</FONT></DIV>
<DIV Class="SyntaxIndented">The sequence of characters in an <FONT FACE="Arial, Helvetica">operator_symbol</FONT>
shall correspond to an operator belonging to one of the six classes of
operators defined in clause <A HREF="AA-4-5.html">4.5</A> (spaces are
not allowed and the case of letters is not significant). </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>11</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">defining_operator_symbol<A NAME="I3025"></A>
::= </FONT><A NAME="I3026"></A><FONT FACE="Arial, Helvetica">operator_symbol</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>12</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">parameter_profile<A NAME="I3027"></A>
::= </FONT>[<A NAME="I3028"></A><FONT FACE="Arial, Helvetica">formal_part</FONT>]</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>13</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">parameter_and_result_profile<A NAME="I3029"></A>
::= </FONT>[<A NAME="I3030"></A><FONT FACE="Arial, Helvetica">formal_part</FONT>] <B>return</B> <A NAME="I3031"></A><FONT FACE="Arial, Helvetica">subtype_mark</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>14</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">formal_part<A NAME="I3032"></A>
::= </FONT><BR>
(<A NAME="I3033"></A><FONT FACE="Arial, Helvetica">parameter_specification</FONT> {; <A NAME="I3034"></A><FONT FACE="Arial, Helvetica">parameter_specification</FONT>})</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>15</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">parameter_specification<A NAME="I3035"></A>
::= </FONT><BR>
<A NAME="I3036"></A><FONT FACE="Arial, Helvetica">defining_identifier_list</FONT> : <A NAME="I3037"></A><FONT FACE="Arial, Helvetica">mode</FONT> <A NAME="I3038"></A><FONT FACE="Arial, Helvetica">subtype_mark</FONT> [:= <A NAME="I3039"></A><FONT FACE="Arial, Helvetica">default_expression</FONT>]<BR>
| <A NAME="I3040"></A><FONT FACE="Arial, Helvetica">defining_identifier_list</FONT> : <A NAME="I3041"></A><FONT FACE="Arial, Helvetica">access_definition</FONT> [:= <A NAME="I3042"></A><FONT FACE="Arial, Helvetica">default_expression</FONT>]</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>16</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">mode<A NAME="I3043"></A>
::= </FONT>[<B>in</B>] | <B>in</B> <B>out</B> | <B>out</B></DIV>
<H4 ALIGN=CENTER>Name Resolution Rules</H4>
<DIV Class="Paranum"><FONT SIZE=-2>17</FONT></DIV>
<DIV Class="Normal"> <A NAME="I3044"></A>A <I>formal parameter</I>
is an object [directly visible within a <FONT FACE="Arial, Helvetica">subprogram_body</FONT>]
that represents the actual parameter passed to the subprogram in a call;
it is declared by a <FONT FACE="Arial, Helvetica">parameter_specification</FONT>.
<A NAME="I3045"></A>For a formal parameter, the expected type for its
<FONT FACE="Arial, Helvetica">default_expression</FONT>, if any, is that
of the formal parameter. <A NAME="I3046"></A></DIV>
<H4 ALIGN=CENTER>Legality Rules</H4>
<DIV Class="Paranum"><FONT SIZE=-2>18</FONT></DIV>
<DIV Class="Normal"> <A NAME="I3047"></A>The <I>parameter mode</I>
of a formal parameter conveys the direction of information transfer with
the actual parameter: <B>in</B>, <B>in out</B>, or <B>out</B>. Mode <B>in</B>
is the default, and is the mode of a parameter defined by an <FONT FACE="Arial, Helvetica">access_definition</FONT>.
The formal parameters of a function, if any, shall have the mode <B>in</B>.
</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>18.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Ramification: </B>Access parameters
are permitted. This restriction to <B>in</B> parameters is primarily
a methodological restriction, though it also simplifies implementation
for some compiler technologies. </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>19</FONT></DIV>
<DIV Class="Normal"> A <FONT FACE="Arial, Helvetica">default_expression</FONT>
is only allowed in a <FONT FACE="Arial, Helvetica">parameter_specification</FONT>
for a formal parameter of mode <B>in</B>.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>20</FONT></DIV>
<DIV Class="Normal"> <A NAME="I3048"></A><A NAME="I3049"></A>A <FONT FACE="Arial, Helvetica">subprogram_declaration</FONT>
or a <FONT FACE="Arial, Helvetica">generic_subprogram_declaration</FONT>
requires a completion: [a body, a <FONT FACE="Arial, Helvetica">renaming_declaration</FONT>
(see <A HREF="AA-8-5.html">8.5</A>), or a <B>pragma</B> Import (see <A HREF="AA-B-1.html">B.1</A>)].
[A completion is not allowed for an <FONT FACE="Arial, Helvetica">abstract_subprogram_declaration</FONT>.]
</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>20.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Ramification: </B>Abstract
subprograms are not declared by <FONT FACE="Arial, Helvetica">subprogram_declaration</FONT>s,
and so do not require completion. Protected subprograms are declared
by <FONT FACE="Arial, Helvetica">subprogram_declaration</FONT>s, and
so require completion. Note that an abstract subprogram is a subprogram,
and a protected subprogram is a subprogram, but a generic subprogram
is not a subprogram. </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>21</FONT></DIV>
<DIV Class="Normal"> A <FONT FACE="Arial, Helvetica">name</FONT> that
denotes a formal parameter is not allowed within the <FONT FACE="Arial, Helvetica">formal_part</FONT>
in which it is declared, nor within the <FONT FACE="Arial, Helvetica">formal_part</FONT>
of a corresponding body or <FONT FACE="Arial, Helvetica">accept_statement</FONT>.
</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>21.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Ramification: </B>By contrast,
<FONT FACE="Arial, Helvetica">generic_formal_parameter_declaration</FONT>s
are visible to subsequent declarations in the same <FONT FACE="Arial, Helvetica">generic_formal_part</FONT>.
</FONT></DIV>
<H4 ALIGN=CENTER>Static Semantics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>22</FONT></DIV>
<DIV Class="Normal"> <A NAME="I3050"></A>The <I>profile</I> of (a
view of) a callable entity is either a <FONT FACE="Arial, Helvetica">parameter_profile</FONT>
or <FONT FACE="Arial, Helvetica">parameter_and_result_profile</FONT>[;
it embodies information about the interface to that entity -- for example,
the profile includes information about parameters passed to the callable
entity. All callable entities have a profile -- enumeration literals,
other subprograms, and entries. An access-to-subprogram type has a designated
profile.] Associated with a profile is a calling convention. A <FONT FACE="Arial, Helvetica">subprogram_declaration</FONT>
declares a procedure or a function, as indicated by the initial reserved
word, with name and profile as given by its specification.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>23</FONT></DIV>
<DIV Class="Normal"> <A NAME="I3051"></A>The nominal subtype of a
formal parameter is the subtype denoted by the <FONT FACE="Arial, Helvetica">subtype_mark</FONT>,
or defined by the <FONT FACE="Arial, Helvetica">access_definition</FONT>,
in the <FONT FACE="Arial, Helvetica">parameter_specification</FONT>.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>24</FONT></DIV>
<DIV Class="Normal"> <A NAME="I3052"></A>An <I>access parameter</I>
is a formal <B>in</B> parameter specified by an <FONT FACE="Arial, Helvetica">access_definition</FONT>.
An access parameter is of an anonymous general access-to-variable type
(see <A HREF="AA-3-10.html">3.10</A>). [Access parameters allow dispatching
calls to be controlled by access values.]</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>25</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> <A NAME="I3053"></A>The
<I>subtypes of a profile</I> are: </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>26</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>For any non-access parameters, the nominal subtype of the
parameter.</LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>27</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>For any access parameters, the designated subtype of the
parameter type.</LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>28</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>For any result, the result subtype. </LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>29</FONT></DIV>
<DIV Class="Normal"> [<A NAME="I3054"></A> The <I>types of a profile</I>
are the types of those subtypes.]</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>30</FONT></DIV>
<DIV Class="Normal"> [A subprogram declared by an <FONT FACE="Arial, Helvetica">abstract_subprogram_declaration</FONT>
is abstract; a subprogram declared by a <FONT FACE="Arial, Helvetica">subprogram_declaration</FONT>
is not. See <A HREF="AA-3-9-3.html">3.9.3</A>, ``<A HREF="AA-3-9-3.html">Abstract
Types and Subprograms</A>''.] </DIV>
<H4 ALIGN=CENTER>Dynamic Semantics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>31</FONT></DIV>
<DIV Class="Normal"> <A NAME="I3055"></A><A NAME="I3056"></A>The elaboration
of a <FONT FACE="Arial, Helvetica">subprogram_declaration</FONT> or an
<FONT FACE="Arial, Helvetica">abstract_subprogram_declaration</FONT>
has no effect. </DIV>
<DIV Class="NotesHeader"><FONT SIZE=-1>NOTES</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>32</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>1 A <FONT FACE="Arial, Helvetica">parameter_specification</FONT>
with several identifiers is equivalent to a sequence of single <FONT FACE="Arial, Helvetica">parameter_specification</FONT>s,
as explained in <A HREF="AA-3-3.html">3.3</A>.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>33</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>2 Abstract subprograms do
not have bodies, and cannot be used in a nondispatching call (see <A HREF="AA-3-9-3.html">3.9.3</A>,
``<A HREF="AA-3-9-3.html">Abstract Types and Subprograms</A>'').</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>34</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>3 The evaluation of <FONT FACE="Arial, Helvetica">default_expression</FONT>s
is caused by certain calls, as described in <A HREF="AA-6-4-1.html">6.4.1</A>.
They are not evaluated during the elaboration of the subprogram declaration.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>35</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>4 Subprograms can be called
recursively and can be called concurrently from multiple tasks. </FONT></DIV>
<H4 ALIGN=CENTER>Examples</H4>
<DIV Class="Paranum"><FONT SIZE=-2>36</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> <I>Examples of
subprogram declarations:</I> </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>37</FONT></DIV>
<DIV Class="Examples"><TT><B>procedure</B> Traverse_Tree;<BR>
<B>procedure</B> Increment(X : <B>in</B> <B>out</B> Integer);<BR>
<B>procedure</B> Right_Indent(Margin : <B>out</B> Line_Size); --<I> see <A HREF="AA-3-5-4.html">3.5.4</A></I><BR>
<B>procedure</B> Switch(From, To : <B>in</B> <B>out</B> Link); --<I> see <A HREF="AA-3-10-1.html">3.10.1</A></I></TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>38</FONT></DIV>
<DIV Class="Examples"><TT><B>function</B> Random <B>return</B> Probability; --<I> see <A HREF="AA-3-5-7.html">3.5.7</A></I></TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>39</FONT></DIV>
<DIV Class="Examples"><TT><B>function</B> Min_Cell(X : Link) <B>return</B> Cell; --<I> see <A HREF="AA-3-10-1.html">3.10.1</A></I><BR>
<B>function</B> Next_Frame(K : Positive) <B>return</B> Frame; --<I> see <A HREF="AA-3-10.html">3.10</A></I><BR>
<B>function</B> Dot_Product(Left, Right : Vector) <B>return</B> Real; --<I> see <A HREF="AA-3-6.html">3.6</A></I></TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>40</FONT></DIV>
<DIV Class="Examples"><TT><B>function</B> "*"(Left, Right : Matrix) <B>return</B> Matrix; --<I> see <A HREF="AA-3-6.html">3.6</A></I></TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>41</FONT></DIV>
<DIV Class="Wide" Style="margin-bottom: 0.4em"> <I>Examples of <B>in</B>
parameters with default expressions:</I> </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>42</FONT></DIV>
<DIV Class="Examples"><TT><B>procedure</B> Print_Header(Pages : <B>in</B> Natural;<BR>
Header : <B>in</B> Line := (1 .. Line'Last => ' '); --<I> see <A HREF="AA-3-6.html">3.6</A></I><BR>
Center : <B>in</B> Boolean := True);</TT></DIV>
<H4 ALIGN=CENTER>Extensions to Ada 83</H4>
<DIV Class="Paranum"><FONT SIZE=-2>42.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><A NAME="I3057"></A>The syntax
for <FONT FACE="Arial, Helvetica">abstract_subprogram_declaration</FONT>
is added. The syntax for <FONT FACE="Arial, Helvetica">parameter_specification</FONT>
is revised to allow for access parameters (see <A HREF="AA-3-10.html">3.10</A>)</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>42.b</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>Program units that are library
units may have a <FONT FACE="Arial, Helvetica">parent_unit_name</FONT>
to indicate the parent of a child (see Section 10). </FONT></DIV>
<H4 ALIGN=CENTER>Wording Changes from Ada 83</H4>
<DIV Class="Paranum"><FONT SIZE=-2>42.c</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>We have incorporated the rules
from RM83-6.5, ``Function Subprograms'' here and in <A HREF="AA-6-3.html">6.3</A>,
``<A HREF="AA-6-3.html">Subprogram Bodies</A>''</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>42.d</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>We have incorporated the definitions
of RM83-6.6, ``Parameter and Result Type Profile - Overloading of Subprograms''
here.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>42.e</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>The syntax rule for <FONT FACE="Arial, Helvetica">defining_operator_symbol</FONT>
is new. It is used for the defining occurrence of an <FONT FACE="Arial, Helvetica">operator_symbol</FONT>,
analogously to <FONT FACE="Arial, Helvetica">defining_identifier</FONT>.
Usage occurrences use the <FONT FACE="Arial, Helvetica">direct_name</FONT>
or <FONT FACE="Arial, Helvetica">selector_name</FONT> syntactic categories.
The syntax rules for <FONT FACE="Arial, Helvetica">defining_designator</FONT>
and <FONT FACE="Arial, Helvetica">defining_program_unit_name</FONT> are
new. </FONT></DIV>
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