projects / OpenSPARC-T2-SAM / blame
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| 55 | <H2><A NAME="SECTION007230000000000000000"></A><A NAME="parenthesized"></A> | |
| 56 | <a id='l2h-340' xml:id='l2h-340'></a> | |
| 57 | <BR> | |
| 58 | 5.2.3 Parenthesized forms | |
| 59 | </H2> | |
| 60 | ||
| 61 | <P> | |
| 62 | A parenthesized form is an optional expression list enclosed in | |
| 63 | parentheses: | |
| 64 | ||
| 65 | <P> | |
| 66 | <dl><dd class="grammar"> | |
| 67 | <div class="productions"> | |
| 68 | <table> | |
| 69 | <tr> | |
| 70 | <td><a id='tok-parenth_form' xml:id='tok-parenth_form'>parenth_form</a></td> | |
| 71 | <td>::=</td> | |
| 72 | <td>"(" [<a class='grammartoken' href="exprlists.html#tok-expression_list">expression_list</a>] ")"</td></tr> | |
| 73 | </table> | |
| 74 | </div> | |
| 75 | <a class="grammar-footer" | |
| 76 | href="grammar.txt" type="text/plain" | |
| 77 | >Download entire grammar as text.</a> | |
| 78 | </dd></dl> | |
| 79 | ||
| 80 | <P> | |
| 81 | A parenthesized expression list yields whatever that expression list | |
| 82 | yields: if the list contains at least one comma, it yields a tuple; | |
| 83 | otherwise, it yields the single expression that makes up the | |
| 84 | expression list. | |
| 85 | ||
| 86 | <P> | |
| 87 | An empty pair of parentheses yields an empty tuple object. Since | |
| 88 | tuples are immutable, the rules for literals apply (i.e., two | |
| 89 | occurrences of the empty tuple may or may not yield the same object). | |
| 90 | <a id='l2h-341' xml:id='l2h-341'></a> | |
| 91 | <P> | |
| 92 | Note that tuples are not formed by the parentheses, but rather by use | |
| 93 | of the comma operator. The exception is the empty tuple, for which | |
| 94 | parentheses <em>are</em> required -- allowing unparenthesized ``nothing'' | |
| 95 | in expressions would cause ambiguities and allow common typos to | |
| 96 | pass uncaught. | |
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| 135 | <span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span> | |
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