Undefined values: Difference between revisions
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{{task}}For languages which have an explicit notion of an undefined value, identify and exercise those language's mechanisms for identifying and manipulating a variable's value's status as being undefined |
{{task}}For languages which have an explicit notion of an undefined value, identify and exercise those language's mechanisms for identifying and manipulating a variable's value's status as being undefined |
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=={{header|ALGOL 68}}== |
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{{works with|ALGOL 68|Revision 1 - no extensions to language used}} |
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{{works with|ALGOL 68G|Any - tested with release [http://sourceforge.net/projects/algol68/files/algol68g/algol68g-1.18.0/algol68g-1.18.0-9h.tiny.el5.centos.fc11.i386.rpm/download 1.18.0-9h.tiny]}} |
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{{works with|ELLA ALGOL 68|Any (with appropriate job cards) - tested with release [http://sourceforge.net/projects/algol68/files/algol68toc/algol68toc-1.8.8d/algol68toc-1.8-8d.fc9.i386.rpm/download 1.8-8d]}} |
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Note: Some implementations (eg [[ALGOL 68C]]) also have a procedure named ''undefined'' that is called to indicated that the behaviour at a particular point in a program is unexpected, undefined, or non-standard. |
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<lang algol68>MODE X = REAL; |
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REF X x := NIL; |
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MODE U = UNION(COMPL, VOID); |
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U u := EMPTY; |
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IF x IS REF X(NIL) THEN |
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print(("x IS NIL", new line)) |
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ELSE |
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print(("x ISNT NIL", new line)) |
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FI; |
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CASE u IN |
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(VOID):print(("u is EMPTY", new line)) |
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OUT print(("u isnt EMPTY", new line)) |
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ESAC</lang> |
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Output: |
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<pre> |
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x IS NIL |
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u is EMPTY |
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</pre> |
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=={{header|C sharp|C#}}== |
=={{header|C sharp|C#}}== |
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