设计模式十三：解释器模式

什么是解释器模式

主要放向：让非初级用户和领域专家使用一门简单的语言来表达想法
一般是高级用户才会有所兴趣。

典型案例

音乐演奏者是现实中解释器模式的例子，
五线谱图形化地表达了声音的音调和持续时间（音乐语言）
音乐演奏者能根据五线谱的符合精确重现声音（语言解释器）

补充知识

领域特定语言(Domain Specific Language ,DSL):针对一个特定领域的有限表达能力的计算机语言。

巴科斯-诺尔形式定义简单语法：
event ::= command token receiver token arguments
command ::= word+
word ::= a collection of one or more alphanumeric characters
token ::= ->
receiver ::= word+
arguments ::= word+

实例代码

from pyparsing import Word,OneOrMore,Optional,Group,Suppress,alphanumsclass Gate:def __init__(self):self.is_open = Falsedef __str__(self):return 'open' if self.is_open else 'closed'def open(self):print('opening the gate')self.is_open = Truedef close(self):print('closing the gate')self.is_open = Falseclass Garage:def __init__(self):self.is_open = Falsedef __str__(self):return 'open' if self.is_open else 'closed'def open(self):print('opening the garage')self.is_open = Truedef close(self):print('closing the garage')self.is_open = Falseclass Aircondition:def __init__(self):self.is_on = Falsedef __str__(self):return 'on' if self.is_on else 'off'def turn_on(self):print('turning on  the aircondition')self.is_open = Truedef turn_off(self):print('turning off the aircondition')self.is_open = Falseclass Heating:def __init__(self):self.is_on = Falsedef __str__(self):return 'on' if self.is_on else 'off'def turn_on(self):print('turning on the heating')self.is_open = Truedef turn_off(self):print('turning off the heating')self.is_open = Falseclass Boiler:def __init__(self):self.temperature = 83 def __str__(self):return 'boiler temperature : {}'.format(self.temperature)def increase_temperature(self,amount):print('increasing the boiler`s temperature by {} degrees'.format(amount))self.temperature += amountdef decrease_temperature(self,amount):print('decreasing the boiler`s temperature by {} degrees'.format(amount))self.temperature -= amountclass Fridge:def __init__(self):self.temperature = 2def __str__(self):return 'fridge temperature: {}'.format(self.temperature)def increase_temperature(self,amount):print('increasing the fridge`s temperature by {} degrees'.format(amount))self.temperature += amountdef decrease_temperature(self,amount):print('decreasing the fridge`s temperature by {} degrees'.format(amount))self.temperature -= amountdef main():# 巴科斯-诺尔形式定义简单语法word = Word(alphanums)command= Group(OneOrMore(word))token = Suppress("->")device = Group(OneOrMore(word))argument = Group(OneOrMore(word))event = command + token + device + Optional(token + argument)# 实例类gate = Gate()garage = Garage()airco = Aircondition()heating = Heating()boiler = Boiler()fridge = Fridge()# 使用语法tests = ('open -> gate','close -> garage','turn on -> aircondition','turn off -> heating','increase -> boiler temperature -> 5 degrees','decrease -> fridge temperature -> 2 degrees')# 解释语法1open_actions = {'gate':gate.open,'garage':garage.open,'aircondition':airco.turn_on,'heating':heating.turn_on,'boiler temperature':boiler.increase_temperature,'fridge temperature':fridge.increase_temperature}# 解释语法2close_actions = {'gate':gate.close,'garage':garage.close,'aircondition':airco.turn_off,'heating':heating.turn_off,'boiler temperature':boiler.decrease_temperature,'fridge temperature':fridge.decrease_temperature}# 分析语言for t in tests:if len(event.parseString(t))==2: # 不带参数cmd,dev = event.parseString(t) # ['turn', 'on'] ['aircondition']cmd_str,dev_str = ' '.join(cmd),' '.join(dev) # 需要以 空格 隔开if 'open' in cmd_str or 'turn on' in cmd_str:open_actions[dev_str]()elif 'close' in cmd_str or 'turn off' in cmd_str:close_actions[dev_str]()elif len(event.parseString(t))==3: # 带参数cmd,dev,arg = event.parseString(t) # ['increase'] ['boiler', 'temperature'] ['5', 'degrees']cmd_str,dev_str,arg_str = ' '.join(cmd),' '.join(dev),' '.join(arg) # 需要以 空格 隔开num_arg = 0try:num_arg = int(arg_str.split()[0])except ValueError as err:print("expected number but got: '{}'".format(arg_str[0]))if 'increase' in  cmd_str and num_arg > 0:open_actions[dev_str](num_arg)elif 'decrease' in cmd_str and num_arg > 0:close_actions[dev_str](num_arg)if __name__ == "__main__":main()

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