Class: Rley::Parser::ParseWalkerFactory

Inherits:
Object
  • Object
show all
Defined in:
lib/rley/parser/parse_walker_factory.rb

Overview

A factory that creates an enumerator that itself walks through a given parsing graph. The walker yields visit events. Terminology warning: this class implements an external iterator for a given GFGParsing object. In other words, its instances are objects distinct for the GFGParsing. This is different from the internal iterators, usually implemented in Ruby with an :each method. Allows to perform a backwards traversal over the relevant parse entries. backwards traversal means that the traversal starts from the accepting (final) parse entries and goes to the initial parse entry. Relevant parse entries are parse entries that "count" in the parse (i.e. they belong to a path that leads to the accepting parse entry)

Instance Method Summary collapse

Instance Method Details

#build_walker(acceptingEntry, maxIndex) ⇒ Object

Build an Enumerator that will yield the parse entries as it walks backwards on the parse graph



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# File 'lib/rley/parser/parse_walker_factory.rb', line 45

def build_walker(acceptingEntry, maxIndex)
  # Local context for the enumerator
  ctx = init_context(acceptingEntry, maxIndex)

  walker = Enumerator.new do |receiver| # 'receiver' is a Yielder
    # At this point: current entry == accepting entry

    loop do
      event = visit_entry(ctx.curr_entry, ctx)
      receiver << event unless event.nil?

      if ctx.curr_entry.orphan? # No antecedent?...
        break if ctx.backtrack_points.empty?
        receiver << use_backtrack_point(ctx)
        receiver << visit_entry(ctx.curr_entry, ctx)
      end

      result = jump_to_antecedent(ctx)
      # Emit detection of scan edge if any...
      receiver << result[0] if result.size > 1
      ctx.curr_entry = result.last
    end
  end

  return walker
end