A function expression is where a function is called and the return value of the function is used as the result of the expression.

For example, if a function is defined that returns the product of two numbers:

func product(a,b)

    return (a*b)

end

Then this function can be used in an expression wherever an rvalue is valid:

a=product(2,3);    // a is set to 6

b=product(2,2)*product(product(2,2),2);    // b is set to 32

A function expression is also an expression that can be said to have ‘side effects’ since it can alter the values of variables.