a basic Regexp-based parser

regexp_parser.rb

# what: a Regexp-based parser.  alainravet - 2016 jan

SYNTAX_RULES = {
    /^PRINT\b/ => {
        /^PRINT\s*\z/   => :new_line_command,
        /^PRINT (.*)/   => :print_command,
    },
    /HELP/i             => :help_command,
}

def command_and_params_for(rules_subtree, text)
  captures = nil
  _, command_or_rules_subtree = rules_subtree.detect{|pattern, _command_or_rules_subtree|
    match = pattern.match(text)
    captures = match.captures if match
  }
  case command_or_rules_subtree
    when Symbol
      command     = command_or_rules_subtree
      parameters  = captures
      [command, parameters]
    when Hash
      rules_subtree = command_or_rules_subtree
      command_and_params_for(rules_subtree, text)
  end
end


# -- TEST -- TEST -- TEST -- TEST -- TEST -- TEST -- TEST -- TEST

def assert_equal(expected, actual)
  unless expected == actual
    raise "\n*** ERROR: \n\texpected: #{expected.inspect}\n\tfound:    #{actual.inspect}"
  end
end

assert_equal [:help_command,     []             ], command_and_params_for(SYNTAX_RULES, 'HELP')
assert_equal [:new_line_command, []             ], command_and_params_for(SYNTAX_RULES, 'PRINT')
assert_equal [:print_command ,   ["hello world"]], command_and_params_for(SYNTAX_RULES, 'PRINT hello world')

puts "SUCCESS"