CoffeeScript 解释器模式

由 珍珍阿姨 创建，Carrie 最后一次修改 2016-08-12 解释器模式问题其他人需要以控制方式运行你的一部分代码。相对地，你选择的语言不能以一种简洁的方式表达问题域。解决方案使用解释器模式来创建一个你翻译为特定代码的领域特异性语言（domain-specific language）。我们来做个假设，例如用户希望在你的应用程序中执行数学运算。你可以让他们正向运行代码来演算指令（eval）但这会让他们运行任意代码。相反，你可以提供一个小型的“堆栈计算器（stack calculator）”语言，用来做单独分析，以便只运行数学运算，同时报告更有用的错误信息。class StackCalculator parseString: (string) -> @stack = [ ] for token in string.split /\s+/ @parseToken token if @stack.length > 1 throw "Not enough operators: numbers left over" else @stack[0] parseToken: (token, lastNumber) -> if isNaN parseFloat(token) # Assume that anything other than a number is an operator @parseOperator token else @stack.push parseFloat(token) parseOperator: (operator) -> if @stack.length < 2 throw "Can't operate on a stack without at least 2 items" right = @stack.pop() left = @stack.pop() result = switch operator when "+" then left + right when "-" then left - right when "*" then left * right when "/" if right is 0 throw "Can't divide by 0" else left / right else throw "Unrecognized operator: #{operator}" @stack.push resultcalc = new StackCalculatorcalc.parseString "5 5 +" # => { result: 10 }calc.parseString "4.0 5.5 +" # => { result: 9.5 }calc.parseString "5 5 + 5 5 + *" # => { result: 100 }try calc.parseString "5 0 /"catch error error # => "Can't divide by 0"try calc.parseString "5 -"catch error error # => "Can't operate on a stack without at least 2 items"try calc.parseString "5 5 5 -"catch error error # => "Not enough operators: numbers left over"try calc.parseString "5 5 5 foo"catch error error # => "Unrecognized operator: foo"讨论作为一种替代编写我们自己的解释器的选择，你可以将现有的CoffeeScript解释器与更自然的（更容易理解的）表达自己的算法的正常方式相结合。class Sandwich constructor: (@customer, @bread='white', @toppings=[], @toasted=false)->white = (sw) -> sw.bread = 'white' swwheat = (sw) -> sw.bread = 'wheat' swturkey = (sw) -> sw.toppings.push 'turkey' swham = (sw) -> sw.toppings.push 'ham' swswiss = (sw) -> sw.toppings.push 'swiss' swmayo = (sw) -> sw.toppings.push 'mayo' swtoasted = (sw) -> sw.toasted = true swsandwich = (customer) -> new Sandwich customerto = (customer) -> customersend = (sw) -> toastedState = sw.toasted and 'a toasted' or 'an untoasted' toppingState = '' if sw.toppings.length > 0 if sw.toppings.length > 1 toppingState = " with #{sw.toppings[0..sw.toppings.length-2].join ', '} and #{sw.toppings[sw.toppings.length-1]}" else toppingState = " with #{sw.toppings[0]}" "#{sw.customer} requested #{toastedState}, #{sw.bread} bread sandwich#{toppingState}"send sandwich to 'Charlie' # => "Charlie requested an untoasted, white bread sandwich"send turkey sandwich to 'Judy' # => "Judy requested an untoasted, white bread sandwich with turkey"send toasted ham turkey sandwich to 'Rachel' # => "Rachel requested a toasted, white bread sandwich with turkey and ham"send toasted turkey ham swiss sandwich to 'Matt' # => "Matt requested a toasted, white bread sandwich with swiss, ham and turkey"这个实例可以允许功能层实现返回修改后的对象，从而外函数可以依次修改它。示例通过借用动词和介词的用法，把自然语法提供给结构，当被正确使用时，会像自然语句一样结束。这样，利用CoffeeScript语言技能和你现有的语言技能可以帮助你关于捕捉代码的问题。