Day10a.rb

class Corrupted < Exception
  def initialize(got)
    @got = got
  end

  attr_reader :got
end

class Parser
  def initialize(text)
    @text = text
    @pos = 0
  end

  def eof?
    @pos >= @text.length
  end

  def peek
    @text[@pos] or raise EOFError
  end

  def pop
    char = peek
    @pos += 1
    char
  end

  def unpop
    @pos -= 1
  end

  def expect(char)
    nchar = pop
    raise Corrupted.new(nchar) if nchar != char
  end

  def parse_chunk
    case nchar = pop
    when '('
      parse_chunk_body ')'
    when '['
      parse_chunk_body ']'
    when '{'
      parse_chunk_body '}'
    when '<'
      parse_chunk_body '>'
    else
      unpop
      raise Corrupted.new(nchar)
    end
  end

  def parse_chunk_body(delim)
    loop do
      if peek == delim
        pop
        break
      end
      parse_chunk
    end
  end
end

Scoring = {
  ')' => 3,
  ']' => 57,
  '}' => 1197,
  '>' => 25137,
}
score = 0
$<.each do |line|
  p = Parser.new(line.chomp)
  p.parse_chunk until p.eof?
rescue EOFError
rescue Corrupted => e
  score += (Scoring[e.got] or 0)
end

print score