sexp_benchmark.rb

require 'benchmark'
require 'sexpistol'
require 'sxp'

require 'strscan'

class Lexer < StringScanner
  def next_token
    # Housekeeping.
    skip /\s*/
    return if eos?

    @token = if scan %r{"([^"]*)"}
      self[1]
    elsif scan %r{ == | [()+*\-] | [a-z_][a-z0-9_]* }ix
      matched.to_sym
    elsif scan %r{[+-]?[0-9][0-9\.]*}
      matched.to_i
    else
      # TODO: Unscan /\r\n|\r|\n/ to get line number.
      near = scan %r{.{0,20}}
      raise "Invalid character at position #{pos} near '#{near}'."
    end
  end
end

class Parser < Lexer
  def self.parse(str)
    Parser.new(str).parse
  end
  
  def parse
    exp = []
    while true
      case next_token
      when :'('
        exp << parse
        raise 'Missing closing parenthesis' if @token != :')'
      when :')'
        break
      when String, Fixnum, Symbol
        exp << @token
      when nil
        break
      end
    end
    exp
  end
end

example_sexp = <<-EOD
((display "This is a test string!")

(define test (lambda () (begin
  (display (+ 1 1))
  (display (+ true true))
  (display (+ false false))
  (display (+ nil nil))
  (display (+ 2 1))
  (display (+ 26 212))
))))
EOD

Benchmark.bmbm do |b|
  b.report("Sexpistol") do
    5000.times do
      parser = Sexpistol.new
      test = parser.parse_string(example_sexp)
    end
  end
  
  b.report("SXP") do
    5000.times do
      test = SXP.read(example_sexp)
    end
  end
  
  b.report("Ary") do
    5000.times do 
      test = Parser.parse(example_sexp)
    end
  end
end