例外を細くしたりする感じの

catch.rb

module Kernel

  def _throw e=RuntimeError, *args, &blk
    if e.kind_of? Exception
      $! = e
      $@ = caller
      throw :exception
    else
      $! = e.new *args, &blk
      $@ = caller
      throw :exception
    end
  end

  def _try &blk
    catch(:exception) do
      ret = blk.call
      return ret
    end
  end

  def _catch type=StandardError, &blk
    case $!
    when type
      ret = blk.call $!
    else
      ret = nil
    end
    return ret
  end

  def _else &blk
    blk.call unless $!
  end

end

_try {
  puts "try"
  _throw
  puts "break"
}

_catch { |e|
  puts "EXCEPTION!"
  puts e.message
  puts $@
}

_try {
  puts "try"
  _throw LoadError
  puts "break"
}

_catch { |e|
  puts "EXCEPTION!"
  puts e.message
  puts $@
}

_catch(LoadError) { |e|
  puts "LOAD ERROR!"
  puts e.message
  puts $@
}