The boolean function returns expression converted to a boolean value.
If the type of expression is string or character, expression is converted to a boolean value with the default formatting set. If expression is a numeric data type (real, money, integer, or long), the result is true if expression is non-zero, false otherwise. If expression is boolean, it is returned without change. For other data types (date or time), the result is undefined.
format (boolean (num), "nonzero ; zero")