A function reference is of the form "#someFunction(a,b,c)". Functions may be defined in the context prior to the
expression being evaluated or within the expression itself using a lambda function definition. For example: Lambda
function definition in an expression: "(#max = {|x,y|$x>$y?$x:$y};max(2,3))" Calling context defined function:
"#isEven(37)". Functions may also be static java methods, registered in the context prior to invocation of the
expression.
Functions are very simplistic, the arguments are not part of the definition (right now),
so the names must be unique.