What is a Pattern?

A Pattern<V> is a value of type V paired with an ordered list of elements, where each element is itself a Pattern<V>. This is the decorated sequence model: the elements form the pattern concept; the value decorates it.

Pattern<V> = { value: V, elements: [Pattern<V>] }

An atomic pattern has no elements — just a value. Any other pattern has both a value and at least one element.

The type is recursive and general-purpose. It can represent anything that has a value and zero or more ordered sub-parts. The most common concrete instantiation is Pattern<Subject>, where each position carries a Subject (identity, labels, properties). This is the type produced by parsing Gram notation.

The value at any position can be read with .value (or .extract() in Rust). The elements are accessible via .elements. Structure is preserved by all operations that transform values — only map and combine change what's stored; neither changes the shape.