module Wool
  module SexpAnalysis
    # This is a simple inherited attribute applied to each node,
    # giving a pointer to that node's next and previous AST node.
    # That way AST traversal is easier.
    module NextPrevAnnotation
      extend BasicAnnotation
      add_properties :next, :prev
      
      # This is the annotator for the next and prev annotation.
      class Annotator
        def annotate!(root)
          children = root.children
          children.each_with_index do |elt, idx|
            # ignore non-sexps. Primitives can't be annotated, sadly.
            if SexpAnalysis::Sexp === elt
              elt.next = children[idx+1]
              elt.prev = children[idx-1] if idx >= 1
            end
          end
        end
      end
      add_annotator Annotator
    end
  end
end