Restrictions on the Use of References to FunctionsIf a reference to a function appears as a symbol in a ground expression, the function
must be capable of taking as input any ground expression and is allowed to return any ground
expression.restrictions on the use of references to
functions
Namely, if a construct &Fname, which is a reference to the function
Fname, appears in a pattern expression or in a result expression, the
function Fname must be declared as either $func Fname e =
e or $func? Fname e = e.