Enum Change 

pub enum Change {
    Target(Graph, Expr),
    Add(Graph, Expr, Placed),
    Replace(Handle, Graph, Expr, Placed),
    Remove(Handle),
}

An edit, each with the graph that reaches it and all the stream plays.

Variants

Target(Graph, Expr)

Add(Graph, Expr, Placed)

Replace(Handle, Graph, Expr, Placed)

Remove(Handle)

A sounding term is cut where the stream stands as the edit is built; what played stays.