SectionP typedef
SectionP =
bool Function(dynamic b)
A more or less direct implementation of Huet's paper
Some inspiration from Clojure's zippers in an attemp to make it generic
The Dart type system definitely leaves room for desire
A predicate to determine if the current node is an Item
or a Section
Implementation
/// A predicate to determine if the current node is an `Item` or a `Section`
typedef SectionP = bool Function(dynamic b);