gistfile1.txt

# A tree structure that contains parse error messages. This can be used to
# give the user a detailed report on what went wrong during a parse. 
#
class(Parslet) ErrorTree: {
  # The parslet that caused the error stored here. 
  attr_reader(parslet)
  # All errors that were encountered when parsing part of this +parslet+. 
  attr_reader(children)
    
  def initialize:(parslet, *children) { # :nodoc:
    @parslet = $parslet
    @children = $children.compact
  }
  
  def nodes: {
    1 + @children.inject(0) do:(sum, node) { $sum + $node.nodes }
  }
  
  def cause: {
    @parslet.cause || "Unknown error in #{parslet.inspect}"
  }
  
  # Returns an ascii tree representation of the causes of this node and its
  # children. 
  #
  def ascii_tree: {
    StringIO.new.tap do:(io) {
      recursive_ascii_tree(@, $io, [true]) 
    }.string
  }
  alias(to_s, ascii_tree)

  def(private) recursive_ascii_tree:(node, stream, curved) {# :nodoc:
    append_prefix($stream, $curved)
    $stream.puts($node.cause)
    
    $node.children.each do:(child) {
      $last_child = ($node.children.last == $child)

      recursive_ascii_tree($child, $stream, $curved + [$last_child])
    }
  }
  def append_prefix:(stream, curved) { # :nodoc:
    $curved[0..-2].each do:(c) {
      $stream.print(if(c) do: { "   " } else: { "|  " })
    }
    $stream.print(if ($curved.last) do: { "`- " } else: { "|- " })
  }
}