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could point to the specific numbers being used for a particular problem. The simple example has its limitation as there are infinitely many real numbers. In various other parts of symbolic programming there are only so many symbols. So to move on to a more significant example, in logic the formula
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are usually implemented using indirection, because otherwise if a value of a data type can contain the entirety of another value of the same data type, there is no limit to the size a value of this data type could need.
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When doing symbolic programming from a formal mathematical specification the use of indirection can be quite helpful. To start with a simple example the variables
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Spinellis, Diomidis (2007). "Another level of indirection". In Oram, Andy; Wilson, Greg (eds.).
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can refer to any number. One could imagine objects for various numbers and then
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there are two levels of indirection here, the first to the set of all
463:. Sebastopol, California: O'Reilly and Associates. pp. 279–291.
391:} means the set of all formulae — so although the reference is to
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and then the second to a specific formula for each occurrence of
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makes use of indirection extensively, a simple example being
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Beautiful Code: Leading
Programmers Explain How They Think
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is another classic example of an indirection pattern. In
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