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<H1> 3.5.1 Enumeration Types</H1>
<DIV Class="Paranum"><FONT SIZE=-2>1</FONT></DIV>
<DIV Class="Normal"> [<A NAME="I1628"></A> An <FONT FACE="Arial, Helvetica">enumeration_type_definition</FONT>
defines an enumeration type.] </DIV>
<H4 ALIGN=CENTER>Syntax</H4>
<DIV Class="Paranum"><FONT SIZE=-2>2</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">enumeration_type_definition<A NAME="I1629"></A>
::= </FONT><BR>
(<A NAME="I1630"></A><FONT FACE="Arial, Helvetica">enumeration_literal_specification</FONT> {, <A NAME="I1631"></A><FONT FACE="Arial, Helvetica">enumeration_literal_specification</FONT>})</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>3</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">enumeration_literal_specification<A NAME="I1632"></A>
::= </FONT> <A NAME="I1633"></A><FONT FACE="Arial, Helvetica">defining_identifier</FONT> | <A NAME="I1634"></A><FONT FACE="Arial, Helvetica">defining_character_literal</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>4</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">defining_character_literal<A NAME="I1635"></A>
::= </FONT><A NAME="I1636"></A><FONT FACE="Arial, Helvetica">character_literal</FONT></DIV>
<H4 ALIGN=CENTER>Legality Rules</H4>
<DIV Class="Paranum"><FONT SIZE=-2>5</FONT></DIV>
<DIV Class="Normal"> [The <FONT FACE="Arial, Helvetica">defining_identifier</FONT>s
and <FONT FACE="Arial, Helvetica">defining_character_literal</FONT>s
listed in an <FONT FACE="Arial, Helvetica">enumeration_type_definition</FONT>
shall be distinct.] </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>5.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Proof: </B>This is a ramification
of the normal disallowance of homographs explicitly declared immediately
in the same declarative region.</FONT></DIV>
<H4 ALIGN=CENTER>Static Semantics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>6</FONT></DIV>
<DIV Class="Normal"> <A NAME="I1637"></A>Each <FONT FACE="Arial, Helvetica">enumeration_literal_specification</FONT>
is the explicit declaration of the corresponding <I>enumeration literal</I>:
it declares a parameterless function, whose defining name is the <FONT FACE="Arial, Helvetica">defining_identifier</FONT>
or <FONT FACE="Arial, Helvetica">defining_character_literal</FONT>, and
whose result type is the enumeration type. </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>6.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Reason: </B>This rule defines
the profile of the enumeration literal, which is used in the various
types of conformance. </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>6.b</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Ramification: </B>The parameterless
function associated with an enumeration literal is fully defined by the
<FONT FACE="Arial, Helvetica">enumeration_type_definition</FONT>; a body
is not permitted for it, and it never fails the Elaboration_Check when
called. </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>7</FONT></DIV>
<DIV Class="Normal"> Each enumeration literal corresponds to a distinct
value of the enumeration type, and to a distinct position number. <A NAME="I1638"></A>The
position number of the value of the first listed enumeration literal
is zero; the position number of the value of each subsequent enumeration
literal is one more than that of its predecessor in the list.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>8</FONT></DIV>
<DIV Class="Normal"> [The predefined order relations between values
of the enumeration type follow the order of corresponding position numbers.]</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>9</FONT></DIV>
<DIV Class="Normal"> [<A NAME="I1639"></A> If the same <FONT FACE="Arial, Helvetica">defining_identifier</FONT>
or <FONT FACE="Arial, Helvetica">defining_character_literal</FONT> is
specified in more than one <FONT FACE="Arial, Helvetica">enumeration_type_definition</FONT>,
the corresponding enumeration literals are said to be <I>overloaded</I>.
At any place where an overloaded enumeration literal occurs in the text
of a program, the type of the enumeration literal has to be determinable
from the context (see <A HREF="AA-8-6.html">8.6</A>).] </DIV>
<H4 ALIGN=CENTER>Dynamic Semantics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>10</FONT></DIV>
<DIV Class="Normal"> <A NAME="I1640"></A><A NAME="I1641"></A><A NAME="I1642"></A>The
elaboration of an <FONT FACE="Arial, Helvetica">enumeration_type_definition</FONT>
creates the enumeration type and its first subtype, which is constrained
to the base range of the type. </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>10.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Ramification: </B>The first
subtype of a discrete type is always constrained, except in the case
of a derived type whose parent subtype is Whatever'Base. </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>11</FONT></DIV>
<DIV Class="Normal"> When called, the parameterless function associated
with an enumeration literal returns the corresponding value of the enumeration
type. </DIV>
<DIV Class="NotesHeader"><FONT SIZE=-1>NOTES</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>12</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>22 If an enumeration literal
occurs in a context that does not otherwise suffice to determine the
type of the literal, then qualification by the name of the enumeration
type is one way to resolve the ambiguity (see <A HREF="AA-4-7.html">4.7</A>).
</FONT></DIV>
<H4 ALIGN=CENTER>Examples</H4>
<DIV Class="Paranum"><FONT SIZE=-2>13</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> <I>Examples of
enumeration types and subtypes: </I></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>14</FONT></DIV>
<DIV Class="Examples"><TT><B>type</B> Day <B>is</B> (Mon, Tue, Wed, Thu, Fri, Sat, Sun);<BR>
<B>type</B> Suit <B>is</B> (Clubs, Diamonds, Hearts, Spades);<BR>
<B>type</B> Gender <B>is</B> (M, F);<BR>
<B>type</B> Level <B>is</B> (Low, Medium, Urgent);<BR>
<B>type</B> Color <B>is</B> (White, Red, Yellow, Green, Blue, Brown, Black);<BR>
<B>type</B> Light <B>is</B> (Red, Amber, Green); <I>-- Red and Green are overloaded</I></TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>15</FONT></DIV>
<DIV Class="Examples"><TT><B>type</B> Hexa <B>is</B> ('A', 'B', 'C', 'D', 'E', 'F');<BR>
<B>type</B> Mixed <B>is</B> ('A', 'B', '*', B, None, '?', '%');</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>16</FONT></DIV>
<DIV Class="Examples"><TT><B>subtype</B> Weekday <B>is</B> Day <B>range</B> Mon .. Fri;<BR>
<B>subtype</B> Major <B>is</B> Suit <B>range</B> Hearts .. Spades;<BR>
<B>subtype</B> Rainbow <B>is</B> Color <B>range</B> Red .. Blue; <I>-- the Color Red, not the Light</I></TT></DIV>
<H4 ALIGN=CENTER>Wording Changes from Ada 83</H4>
<DIV Class="Paranum"><FONT SIZE=-2>16.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>The syntax rule for <FONT FACE="Arial, Helvetica">defining_character_literal</FONT>
is new. It is used for the defining occurrence of a <FONT FACE="Arial, Helvetica">character_literal</FONT>,
analogously to <FONT FACE="Arial, Helvetica">defining_identifier</FONT>.
Usage occurrences use the <FONT FACE="Arial, Helvetica">name</FONT> or
<FONT FACE="Arial, Helvetica">selector_name</FONT> syntactic categories.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>16.b</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>We emphasize the fact that an
enumeration literal denotes a function, which is called to produce a
value. </FONT></DIV>
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