TALES 'not' expressions

A not: expression is immediately followed by another expression - indicating a value. That following expression is evaluated as a completely independent expression in its own right, starting with an optional prefix, or treated as a path: expression if it has no prefix.

Once the value of the expression following the not: prefix has been determined, its value is interpreted as a boolean using the method below. Finally, that boolean value is inverted (a logical not).

Special rules for boolean interpretation

The not: expression has specific rules for interpreting values as booleans; these rules differ from the normal boolean coercion rules. The following rules are processed in the order listed:

1. If the value cancels the action then it is interpreted as false.
2. If the value is a null reference, then it is interpreted as false.
3. If the value is a System.Boolean then it is interpreted as its boolean value.
4. If the value is of any numeric type and equals zero, then it is interpreted as false.
5. If the value is System.Collections.IEnumerable then it is interpreted as true if it contains any items. Otherwise (if it is an empty collection) then it is interpreted as false.
6. If the value is of a type which implements CSF.Zpt.Tales.ITalesConvertible then the AsBoolean() method is called from the value and the result of that method is used as the boolean interpretation.
7. All other values (numeric values other than zero, all non-empty strings, all other value-type values, and all other non-null reference-type instances) are interpreted as true.