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<H1> 4.4 Expressions</H1>
<DIV Class="Paranum"><FONT SIZE=-2>1</FONT></DIV>
<DIV Class="Normal"> <A NAME="I2331"></A>An <I>expression</I> is a
formula that defines the computation or retrieval of a value. In this
International Standard, the term ``expression'' refers to a construct
of the syntactic category <FONT FACE="Arial, Helvetica">expression</FONT>
or of any of the other five syntactic categories defined below. <A NAME="I2332"></A><A NAME="I2333"></A><A NAME="I2334"></A><A NAME="I2335"></A><A NAME="I2336"></A><A NAME="I2337"></A><A NAME="I2338"></A><A NAME="I2339"></A><A NAME="I2340"></A><A NAME="I2341"></A><A NAME="I2342"></A><A NAME="I2343"></A><A NAME="I2344"></A><A NAME="I2345"></A><A NAME="I2346"></A><A NAME="I2347"></A><A NAME="I2348"></A><A NAME="I2349"></A><A NAME="I2350"></A><A NAME="I2351"></A><A NAME="I2352"></A><A NAME="I2353"></A><A NAME="I2354"></A><A NAME="I2355"></A><A NAME="I2356"></A><A NAME="I2357"></A><A NAME="I2358"></A><A NAME="I2359"></A><A NAME="I2360"></A><A NAME="I2361"></A><A NAME="I2362"></A><A NAME="I2363"></A><A NAME="I2364"></A><A NAME="I2365"></A><A NAME="I2366"></A><A NAME="I2367"></A><A NAME="I2368"></A><A NAME="I2369"></A><A NAME="I2370"></A><A NAME="I2371"></A><A NAME="I2372"></A><A NAME="I2373"></A><A NAME="I2374"></A><A NAME="I2375"></A><A NAME="I2376"></A><A NAME="I2377"></A><A NAME="I2378"></A><A NAME="I2379"></A><A NAME="I2380"></A><A NAME="I2381"></A><A NAME="I2382"></A><A NAME="I2383"></A><A NAME="I2384"></A><A NAME="I2385"></A><A NAME="I2386"></A><A NAME="I2387"></A><A NAME="I2388"></A><A NAME="I2389"></A><A NAME="I2390"></A><A NAME="I2391"></A><A NAME="I2392"></A><A NAME="I2393"></A><A NAME="I2394"></A><A NAME="I2395"></A><A NAME="I2396"></A><A NAME="I2397"></A><A NAME="I2398"></A><A NAME="I2399"></A><A NAME="I2400"></A><A NAME="I2401"></A><A NAME="I2402"></A><A NAME="I2403"></A></DIV>
<H4 ALIGN=CENTER>Syntax</H4>
<DIV Class="Paranum"><FONT SIZE=-2>2</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">expression<A NAME="I2404"></A>
::= </FONT><BR>
<A NAME="I2405"></A><FONT FACE="Arial, Helvetica">relation</FONT> {<B>and</B> <A NAME="I2406"></A><FONT FACE="Arial, Helvetica">relation</FONT>} | <A NAME="I2407"></A><FONT FACE="Arial, Helvetica">relation</FONT> {<B>and</B> <B>then</B> <A NAME="I2408"></A><FONT FACE="Arial, Helvetica">relation</FONT>}<BR>
| <A NAME="I2409"></A><FONT FACE="Arial, Helvetica">relation</FONT> {<B>or</B> <A NAME="I2410"></A><FONT FACE="Arial, Helvetica">relation</FONT>} | <A NAME="I2411"></A><FONT FACE="Arial, Helvetica">relation</FONT> {<B>or</B> <B>else</B> <A NAME="I2412"></A><FONT FACE="Arial, Helvetica">relation</FONT>}<BR>
| <A NAME="I2413"></A><FONT FACE="Arial, Helvetica">relation</FONT> {<B>xor</B> <A NAME="I2414"></A><FONT FACE="Arial, Helvetica">relation</FONT>}</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>3</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">relation<A NAME="I2415"></A>
::= </FONT><BR>
<A NAME="I2416"></A><FONT FACE="Arial, Helvetica">simple_expression</FONT> [<A NAME="I2417"></A><FONT FACE="Arial, Helvetica">relational_operator</FONT> <A NAME="I2418"></A><FONT FACE="Arial, Helvetica">simple_expression</FONT>]<BR>
| <A NAME="I2419"></A><FONT FACE="Arial, Helvetica">simple_expression</FONT> [<B>not</B>] <B>in</B> <A NAME="I2420"></A><FONT FACE="Arial, Helvetica">range</FONT><BR>
| <A NAME="I2421"></A><FONT FACE="Arial, Helvetica">simple_expression</FONT> [<B>not</B>] <B>in</B> <A NAME="I2422"></A><FONT FACE="Arial, Helvetica">subtype_mark</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>4</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">simple_expression<A NAME="I2423"></A>
::= </FONT>[<A NAME="I2424"></A><FONT FACE="Arial, Helvetica">unary_adding_operator</FONT>] <A NAME="I2425"></A><FONT FACE="Arial, Helvetica">term</FONT> {<A NAME="I2426"></A><FONT FACE="Arial, Helvetica">binary_adding_operator</FONT> <A NAME="I2427"></A><FONT FACE="Arial, Helvetica">term</FONT>}</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>5</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">term<A NAME="I2428"></A>
::= </FONT><A NAME="I2429"></A><FONT FACE="Arial, Helvetica">factor</FONT> {<A NAME="I2430"></A><FONT FACE="Arial, Helvetica">multiplying_operator</FONT> <A NAME="I2431"></A><FONT FACE="Arial, Helvetica">factor</FONT>}</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>6</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">factor<A NAME="I2432"></A>
::= </FONT><A NAME="I2433"></A><FONT FACE="Arial, Helvetica">primary</FONT> [** <A NAME="I2434"></A><FONT FACE="Arial, Helvetica">primary</FONT>] | <B>abs</B> <A NAME="I2435"></A><FONT FACE="Arial, Helvetica">primary</FONT> | <B>not</B> <A NAME="I2436"></A><FONT FACE="Arial, Helvetica">primary</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>7</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">primary<A NAME="I2437"></A>
::= </FONT><BR>
<A NAME="I2438"></A><FONT FACE="Arial, Helvetica">numeric_literal</FONT> | <B>null</B> | <A NAME="I2439"></A><FONT FACE="Arial, Helvetica">string_literal</FONT> | <A NAME="I2440"></A><FONT FACE="Arial, Helvetica">aggregate</FONT><BR>
| <A NAME="I2441"></A><FONT FACE="Arial, Helvetica">name</FONT> | <A NAME="I2442"></A><FONT FACE="Arial, Helvetica">qualified_expression</FONT> | <A NAME="I2443"></A><FONT FACE="Arial, Helvetica">allocator</FONT> | (<A NAME="I2444"></A><FONT FACE="Arial, Helvetica">expression</FONT>)</DIV>
<H4 ALIGN=CENTER>Name Resolution Rules</H4>
<DIV Class="Paranum"><FONT SIZE=-2>8</FONT></DIV>
<DIV Class="Normal"> A <FONT FACE="Arial, Helvetica">name</FONT> used
as a <FONT FACE="Arial, Helvetica">primary</FONT> shall resolve to denote
an object or a value. </DIV>
<H4 ALIGN=CENTER>Static Semantics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>9</FONT></DIV>
<DIV Class="Normal"> Each expression has a type; it specifies the computation
or retrieval of a value of that type. </DIV>
<H4 ALIGN=CENTER>Dynamic Semantics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>10</FONT></DIV>
<DIV Class="Normal"> <A NAME="I2445"></A>The value of a <FONT FACE="Arial, Helvetica">primary</FONT>
that is a <FONT FACE="Arial, Helvetica">name</FONT> denoting an object
is the value of the object. </DIV>
<H4 ALIGN=CENTER>Implementation Permissions</H4>
<DIV Class="Paranum"><FONT SIZE=-2>11</FONT></DIV>
<DIV Class="Normal"> <A NAME="I2446"></A><A NAME="I2447"></A><A NAME="I2448"></A>For
the evaluation of a <FONT FACE="Arial, Helvetica">primary</FONT> that
is a <FONT FACE="Arial, Helvetica">name</FONT> denoting an object of
an unconstrained numeric subtype, if the value of the object is outside
the base range of its type, the implementation may either raise Constraint_Error
or return the value of the object. </DIV>
<H4 ALIGN=CENTER>Examples</H4>
<DIV Class="Paranum"><FONT SIZE=-2>12</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> <I>Examples of
primaries:</I> </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>13</FONT></DIV>
<DIV Class="Examples" Style="margin-bottom: 0.9em"><TT>4.0 <I>-- real literal</I><BR>
Pi <I>-- named number</I><BR>
(1 .. 10 => 0) <I>-- array aggregate</I><BR>
Sum <I>-- variable</I><BR>
Integer'Last <I>-- attribute</I><BR>
Sine(X) <I>-- function call</I><BR>
Color'(Blue) <I>-- qualified expression</I><BR>
Real(M*N) <I>-- conversion</I><BR>
(Line_Count + 10) <I>-- parenthesized expression </I></TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>14</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> <I>Examples of
expressions:</I> </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>15</FONT></DIV>
<DIV Class="Examples"><TT>Volume <I>-- primary</I><BR>
<B>not</B> Destroyed <I>-- factor</I><BR>
2*Line_Count <I>-- term </I><BR>
-4.0 <I>-- simple expression</I><BR>
-4.0 + A <I>-- simple expression</I><BR>
B**2 - 4.0*A*C <I>-- simple expression</I><BR>
Password(1 .. 3) = "Bwv" <I>-- relation</I><BR>
Count <B>in</B> Small_Int <I>-- relation</I><BR>
Count <B>not</B> <B>in</B> Small_Int <I>-- relation</I><BR>
Index = 0 <B>or</B> Item_Hit <I>-- expression</I><BR>
(Cold <B>and</B> Sunny) <B>or</B> Warm <I>-- expression (parentheses are required)</I><BR>
A**(B**C) <I>-- expression (parentheses are required)</I></TT></DIV>
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