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Undefined values: Difference between revisions
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=={{header|Seed7}}==
Seed7 variables are initialized, when they are defined.
This way a variable can never have an undefined value.
There is also no general NULL value.
When there is a need for a NULL value, an interface type can define its own NULL value.
E.g.: The interface type [http://seed7.sourceforge.net/libraries/file.htm file] defines
[http://seed7.sourceforge.net/libraries/null_file.htm#STD_NULL STD_NULL],
which is used to initialize file variables and as result of
[http://seed7.sourceforge.net/libraries/external_file.htm#open%28in_string,in_string%29 open],
when a file cannot be opened.
=={{header|Tcl}}==
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