Undefined values: Difference between revisions
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({{task|Programming language concepts}}) |
(GP and PARI) |
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Explicitly checking the status of a variable with <code>IsFree</code> is discouraged because it can introduce race conditions. |
Explicitly checking the status of a variable with <code>IsFree</code> is discouraged because it can introduce race conditions. |
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=={{header|PARI/GP}}== |
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In GP, undefined variables test equal to the monomial in the variable with the name of that variable. So to test if <var>v</var> is undefined, do |
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<lang parigp>v == 'v</lang> |
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In PARI, you can do the same but the function <code>is_entry()</code> is more appropriate: |
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<lang C>is_entry("v") == NULL;</lang> |
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=={{header|Perl}}== |
=={{header|Perl}}== |