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Undefined values: Difference between revisions
Explained Oz.
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(Explained Oz.) |
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</lang>
=={{header|Oz}}==
A program that uses an undefined variable does not compile.
However, variables can be "unbound" or "free". If a program tries to read such a variable, the current thread will be suspended until the variable's value becomes determined.
<lang oz>declare X in
thread
if {IsFree X} then {System.showInfo "X is unbound."} end
{Wait X}
{System.showInfo "Now X is determined."}
end
{System.showInfo "Sleeping..."}
{Delay 1000}
{System.showInfo "Setting X."}
X = 42</lang>
Explicitly checking the status of a variable with <code>IsFree</code> is discouraged because it can introduce race conditions.
=={{header|Perl}}==
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