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class Lisp
  def initialize
    @env = { 
      :label => lambda { |(name,val), _| @env[name] = val },
      :quote => lambda { |sexpr, _| sexpr[0] },
      :car   => lambda { |(list), _| list[0] },
      :cdr   => lambda { |(list), _| list.drop 1 },
      :cons  => lambda { |(e,cell), _| [e] + cell },
      :eq    => lambda { |(l,r), _| l == r },
      :if    => lambda { |(cond, thn, els), ctx| eval(cond, ctx) ? eval(thn, ctx) : eval(els, ctx) },

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#如何将 Rails 应用程序部署到 VPS 上

如果已经在 VPS 上假设好了 Rails 生产环境，接下来就可以将部署应用程序了。

###需要用到的工具

• capistrano

---

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# From http://www.mattsears.com/articles/2011/11/27/ruby-blocks-as-dynamic-callbacks

class Proc
  def callback(callable, *args)
    self === Class.new do
      method_name = callable.to_sym
      define_method(method_name) { |&block| block.nil? ? true : block.call(*args) }
      define_method("#{method_name}?") { true }
      def method_missing(method_name, *args, &block) false; end
    end.new

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module Rubber

  def self.try(diftimes = [3, 8, 2], options = { }, &block)
    val = timeout(diftimes.shift) do
      block.call
    end
  rescue options[:on] || Exception => e
    Rails.logger.info("#{Time.now}:#{__FILE__}:#{__LINE__}}:#{e.backtrace.join("\n")}")
    retry if diftimes.first
    return ""