The XPRESS language makes no distinction between a function call and what languages such as C refer to as an expression operator. This results in a syntactical style known as prefix notation. Prefix notation differs from the more common infix notation in that the operator of an expression is written first, followed by the operands. For example, consider the following simple logical expression written in C using infix notation:

x == 42

If C used prefix notation, the previous statement would be written:

== x 42

If C provided no expression operators and instead supplied only functions, the statement could be written as follows:

equals(x, 42)

Prefix notation is easily understood if you think in terms of calling functions rather than writing expressions.

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