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Null object: Difference between revisions
Added Oz explanation.
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=={{header|Oz}}==
There is no explicit null in Oz.
===Unbound variables===
If an unbound variable is accessed, the current thread will be suspended:
<lang oz>declare
X
in
{Show X+2} %% blocks</lang>
If you later assign a value to X in another thread, the original thread will resume and print the result of the addition. This is the basic building block of Oz' [http://c2.com/cgi/wiki?DeclarativeConcurrency declarative concurrency].
===Undefined values===
Access to undefined values will usually provoke an exception in Oz.
It is also possible to assign a unique "failed" value to a variable. Such a failed value encapsulates an exception. This can be useful in concurrent programming.
<lang oz>declare
X = {Value.failed dontTouchMe}
in
{Wait X} %% throws dontTouchMe</lang>
Sometimes algebraic data types like Haskell's Maybe are simulated using records.
<lang oz>declare
X = just("Data")
in
case X of nothing then skip
[] just(Result) then {Show Result}
end</lang>
=={{header|Perl}}==
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