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Encyclopedia > Prefix notation

Polish notation, also known as prefix notation was created by Jan Łukasiewicz. Operators are placed before operands.

` + 1 2 `

Yields (as expected) 3.

It is not limited to only two values, nor to just addition.

` (* (+ 0 1) (+ 2 3)) `

Returns 5.

While the examples above use parantheses, one of the benefits of Polish notation is that, assuming the arity of each operator is known, parentheses are unnecessary: the order of operations is unique and easy to determine, if the expression is known to be correct. For example, assuming * and + are binary,

` * + 0 1 + 2 3 `

can refer only to

` (* (+ 0 1) (+ 2 3)) `

Polish notation is used in computer programming languages Lisp, Scheme (based on Lisp), and some others.

Results from FactBites:

 PHP - Wikipedia, the free encyclopedia (1746 words) Variables are prefixed with a dollar symbol and no type need be specified in advance. Integer variables can be assigned using decimal (positive and negative), octal and hexadecimal notations. They can be specified using floating point notation, or two forms of scientific notation.
 The skew.org XML Tutorial (8463 words) This notation is described briefly in section 6 of the spec. There is also a rarely-used declaration called a notation, which creates a name-location pair that can be used to signal to an application that a parsed character data section is to be interpreted as having some kind of additional encoding, such as Base64 or PostScript. The "xml:" prefix does not have to be declared in an xmlns:xml attribute, though; the XML Namespaces recommendation says that xml: is by default bound to a particular namespace.
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