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Boolean values: Difference between revisions
added common lisp, scheme
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* any pointer type, where the null pointer gives false and any other pointer gives true
* any user-defined type with an implicit conversion operator either to <code>bool</code> or to a built-in type which itself can be converted to <code>bool</code> (i.e. any of the above). The C++ standard library contains one such implicit conversion: the implicit conversion of a stream <code>s</code> to <code>bool</code> gives <code>!s.fail()</code>
=={{header|Common Lisp}}==
The only value in Common Lisp that is false is <tt>nil</tt>, the empty list.
Everything else is true. The constant <tt>t</tt> represents the canonical true value.
=={{header|E}}==
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<code>false</code>, <code>nil</code> and <code>true</code> are singleton instances of classes <code>FalseClass</code>, <code>NilClass</code> and <code>TrueClass</code> respectively.
[http://www.ruby-doc.org/docs/ProgrammingRuby/html/tut_expressions.html#UF]
=={{header|Scheme}}==
The only value in Scheme that is false is <tt>#f</tt>.
Everything else (including the empty list, unlike Lisp) is true. The constant <tt>#t</tt> represents the canonical true value.
=={{header|Tcl}}==
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