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@website https://tridiamond.tech **/\n\nlet node = {\n type: 'MultiplicativeExpression',\n operator: '*',\n children: []\n}","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"然后我们把 source 的前三项都用 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":".shift()","attrs":{}}],"attrs":{}},{"type":"text","text":" 获取出来放入 node 的 children 里面，最后把新生成的结构放回 source 里面。最后同样我们需要去递归一次。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"javascript"},"content":[{"type":"text","text":"/** Crafted by 三钻 **/\n/** @website https://tridiamond.tech **/\n\n/**\n * 乘法表达式\n * @param source\n */\nfunction MultiplicativeExpression(source) {\n // Number 类型\n if (source[0].type === 'Number') {\n let node = {\n type: 'MultiplicativeExpression',\n children: [source[0]],\n };\n source[0] = node;\n return MultiplicativeExpression(source);\n }\n // 乘法\n if (source[0].type === 'MultiplicativeExpression' && source[1] && source[1].type === '*') {\n let node = {\n type: 'MultiplicativeExpression',\n operator: '*',\n children: [],\n };\n node.children.push(source.shift());\n node.children.push(source.shift());\n node.children.push(source.shift());\n source.unshift(node);\n return MultiplicativeExpression(source);\n }\n}","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"除法与乘法的逻辑没有任何的本质区别，就是抄写一遍，把乘号变成了除号而已。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"javascript"},"content":[{"type":"text","text":"/** Crafted by 三钻 **/\n/** @website https://tridiamond.tech **/\n\n/**\n * 乘法表达式\n * @param source\n */\nfunction MultiplicativeExpression(source) {\n // Number 类型\n if (source[0].type === 'Number') {\n let node = {\n type: 'MultiplicativeExpression',\n children: [source[0]],\n };\n source[0] = node;\n return MultiplicativeExpression(source);\n }\n // 乘法\n if (source[0].type === 'MultiplicativeExpression' && source[1] && source[1].type === '*') {\n let node = {\n type: 'MultiplicativeExpression',\n operator: '*',\n children: [],\n };\n node.children.push(source.shift());\n node.children.push(source.shift());\n node.children.push(source.shift());\n source.unshift(node);\n return MultiplicativeExpression(source);\n }\n // 除法\n if (source[0].type === 'MultiplicativeExpression' && source[1] && source[1].type === '/') {\n let node = {\n type: 'MultiplicativeExpression',\n operator: '/',\n children: [],\n };\n node.children.push(source.shift());\n node.children.push(source.shift());\n node.children.push(source.shift());\n source.unshift(node);\n return MultiplicativeExpression(source);\n 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source[0]","attrs":{}}],"attrs":{}},{"type":"text","text":"，这就说明我们已经把所有的乘法都处理完毕了。因为除了乘法和除法，我们还有可能遇到不认识的情况，所以这里最后我们加了一个默认递归自己，","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"return MultiplicativeExpression(source);","attrs":{}}],"attrs":{}},{"type":"text","text":"。但是现实中是不应该有这种情况的，我们最后这里加的这个 return 应该是永远不会执行的。因为如果遇到了不符合的字符，那肯定就已经在前面的步骤被退出了。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"最后我们的代码如下：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"javascript"},"content":[{"type":"text","text":"/** Crafted by 三钻 **/\n/** @website https://tridiamond.tech **/\n\n/**\n * 乘法表达式\n * @param source\n */\nfunction MultiplicativeExpression(source) {\n // Number 类型\n if (source[0].type === 'Number') {\n let node = {\n type: 'MultiplicativeExpression',\n children: [source[0]],\n };\n source[0] = node;\n return MultiplicativeExpression(source);\n }\n // 乘法\n if (source[0].type === 'MultiplicativeExpression' && source[1] && source[1].type === '*') {\n let node = {\n type: 'MultiplicativeExpression',\n operator: '*',\n children: [],\n };\n node.children.push(source.shift());\n node.children.push(source.shift());\n node.children.push(source.shift());\n source.unshift(node);\n return MultiplicativeExpression(source);\n }\n // 除法\n if (source[0].type === 'MultiplicativeExpression' && source[1] && source[1].type === '/') {\n let node = {\n type: 'MultiplicativeExpression',\n operator: '/',\n children: [],\n };\n node.children.push(source.shift());\n node.children.push(source.shift());\n node.children.push(source.shift());\n source.unshift(node);\n return MultiplicativeExpression(source);\n }\n \n if (source[0].type === 'MultiplicativeExpression') {\n return source[0];\n }\n \n return MultiplicativeExpression(source);\n}","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如果我们进入调试模式，走一篇代码的话，首先刚进入 MultiplicativeExpression 的时候，我们的 source 就是通过 tokenize() 函数之后的结果。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如果我们的 source 是 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"10 * 25","attrs":{}}],"attrs":{}},{"type":"text","text":"，那么 MultiplicativeExpression 执行完毕之后，我们 source 数组最后只会有两个元素，一个 type 是 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"MultiplicativeExpression","attrs":{}}],"attrs":{}},{"type":"text","text":"，另一个 type 是 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"EOF","attrs":{}}],"attrs":{}},{"type":"text","text":"。因为在我们处理 MultiplicativeExpression 的时候已经把所有属于 MultiplicativeExpression 的节点合并到 MultiplicativeExpression 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","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"MultiplicativeExpression","attrs":{}}],"attrs":{}},{"type":"text","text":"多执行一行。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"多说只会懵，我们直接来看看代码是如何实现，可能不用再读百变也会其义自见了！哈哈。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"javascript"},"content":[{"type":"text","text":"/** Crafted by 三钻 **/\n/** @website https://tridiamond.tech **/\n\n/**\n * 加法表达式\n * @param source\n */\nfunction AdditiveExpression(source) {\n // 第一个遇到乘法表达式时\n if (source[0].type === 'MultiplicativeExpression') {\n let node = {\n type: 'AdditiveExpression',\n children: [source[0]],\n };\n source[0] = node;\n return AdditiveExpression(source);\n }\n // 加法\n if (source[0].type === 'AdditiveExpression' && source[1] && source[1].type === '+') {\n let node = {\n type: 'AdditiveExpression',\n operator: '+',\n children: [],\n };\n node.children.push(source.shift());\n node.children.push(source.shift());\n MultiplicativeExpression(source);\n node.children.push(source.shift());\n source.unshift(node);\n return AdditiveExpression(source);\n }\n // 减法\n if (source[0].type === 'AdditiveExpression' && source[1] && source[1].type === '-') {\n let node = {\n type: 'AdditiveExpression',\n operator: '-',\n children: [],\n };\n node.children.push(source.shift());\n node.children.push(source.shift());\n MultiplicativeExpression(source);\n node.children.push(source.shift());\n source.unshift(node);\n return AdditiveExpression(source);\n }\n\n if (source[0].type === 'AdditiveExpression') {\n return source[0];\n }\n\n MultiplicativeExpression(source);\n return AdditiveExpression(source);\n}","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"Expression","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"那么最后我们就是实现我们的 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"整体的表达式","attrs":{}}],"attrs":{}},{"type":"text","text":" 。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"其实最后这个步骤就是把 Expression 的整体加上 EOF 的结构，然后给他产生一下。进入 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"Expression()","attrs":{}}],"attrs":{}},{"type":"text","text":" 的时候我们就判断一下 source 的第一个元素是不是 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"AdditiveExpression","attrs":{}}],"attrs":{}},{"type":"text","text":"。因为它同样会包含了 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"AdditiveExpression","attrs":{}}],"attrs":{}},{"type":"text","text":"的所有逻辑，所以这里判断 source 第一个是 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"AdditiveExpression","attrs":{}}],"attrs":{}},{"type":"text","text":"，然后第二个是 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"EOF","attrs":{}}],"attrs":{}},{"type":"text","text":" 的话，Expression 就会总结，然后给我们的 source resolve 成一个最终节点。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"我们来看看 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"Expression()","attrs":{}}],"attrs":{}},{"type":"text","text":"函数的 代码：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"javascript"},"content":[{"type":"text","text":"/** Crafted by 三钻 **/\n/** @website https://tridiamond.tech **/\n\n/**\n * 表达式\n * @param tokens\n */\nfunction Expression(tokens) {\n if (source[0].type === 'AdditiveExpression' && source[1] && source[1].type === 'EOF') {\n let node = {\n type: 'Expression',\n children: [source.shift(), source.shift()],\n };\n source.unshift(node);\n return node;\n }\n AdditiveExpression(source);\n return Expression(source);\n}","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"最后我们来看看整个 LL 语法分析的代码：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"javascript"},"content":[{"type":"text","text":"/** Crafted by 三钻 **/\n/** @website https://tridiamond.tech **/\n\n// 正则表达式\nlet regexp = /([0-9\\.]+)|([ \\t]+)|([\\r\\n]+)|(\\*)|(\\/)|(\\+)|(\\-)/g;\n// 正则分支名字\nlet dictionary = ['Number', 'Whitespace', 'LineTerminator', '*', '/', '+', '-'];\n\n// 接下来我们就可以去做 `tokenize`\nfunction* tokenize(source) {\n let result = null;\n let lastIndex = 0;\n while (true) {\n // 每次去取出 lastIndex\n lastIndex = regexp.lastIndex;\n\n // 使用正则表达式里面的 `exec` 函数，去让它不断的扫描整个原字符里面的内容。\n result = regexp.exec(source);\n\n // result 里面没有东西就直接退出\n if (!result) break;\n\n // 与新生成的 lastIndex 去做比较\n // 如果长度超了，那就说明，这里面有我们不认识的字符或者格式\n if (regexp.lastIndex - lastIndex > result[0].length) break;\n\n // 定义一个 token 变量\n let token = {\n type: null,\n value: null,\n };\n\n // 如果 result 里面有东西\n // 那我们就根据 result 的位置\n // 从 1 到 7 的范围里面匹配到哪一种输入元素\n //（ 首先正则返回的第 0 个是整个结果，所以我们从 1 开始\n // 然后我们的匹配总数一个有 7 个所以是从 1 到 7 ）\n for (let i = 1; i <= dictionary.length; i++) {\n // result 中有值，就存储当前类型\n if (result[i]) token.type = dictionary[i - 1];\n }\n // 这里存储值\n token.value = result[0];\n yield token;\n }\n\n yield {\n type: 'EOF',\n };\n}\n\nlet source = [];\n\nfor (let token of tokenize('10 + 20 + 30')) {\n if (token.type !== 'Whitespace' && token.type !== 'LineTerminator') source.push(token);\n}\n\n/**\n * 表达式\n * @param tokens\n */\nfunction Expression(tokens) {\n if (source[0].type === 'AdditiveExpression' && source[1] && source[1].type === 'EOF') {\n let node = {\n type: 'Expression',\n children: [source.shift(), source.shift()],\n };\n source.unshift(node);\n return node;\n }\n AdditiveExpression(source);\n return Expression(source);\n}\n\n/**\n * 加法表达式\n * @param source\n */\nfunction AdditiveExpression(source) {\n // 第一个遇到乘法表达式时\n if (source[0].type === 'MultiplicativeExpression') {\n let node = {\n type: 'AdditiveExpression',\n children: [source[0]],\n };\n source[0] = node;\n return AdditiveExpression(source);\n }\n // 加法\n if (source[0].type === 'AdditiveExpression' && source[1] && source[1].type === '+') {\n let node = {\n type: 'AdditiveExpression',\n operator: '+',\n children: [],\n };\n node.children.push(source.shift());\n node.children.push(source.shift());\n MultiplicativeExpression(source);\n node.children.push(source.shift());\n source.unshift(node);\n return AdditiveExpression(source);\n }\n // 减法\n if (source[0].type === 'AdditiveExpression' && source[1] && source[1].type === '-') {\n let node = {\n type: 'AdditiveExpression',\n operator: '-',\n children: [],\n };\n node.children.push(source.shift());\n node.children.push(source.shift());\n MultiplicativeExpression(source);\n node.children.push(source.shift());\n source.unshift(node);\n return AdditiveExpression(source);\n }\n\n if (source[0].type === 'AdditiveExpression') {\n return source[0];\n }\n\n MultiplicativeExpression(source);\n return AdditiveExpression(source);\n}\n\n/**\n * 乘法表达式\n * @param source\n */\nfunction MultiplicativeExpression(source) {\n // Number 类型\n if (source[0].type === 'Number') {\n let node = {\n type: 'MultiplicativeExpression',\n children: [source[0]],\n };\n source[0] = node;\n return MultiplicativeExpression(source);\n }\n // 乘法\n if (source[0].type === 'MultiplicativeExpression' && source[1] && source[1].type === '*') {\n let node = {\n type: 'MultiplicativeExpression',\n operator: '*',\n children: [],\n };\n node.children.push(source.shift());\n node.children.push(source.shift());\n node.children.push(source.shift());\n source.unshift(node);\n return MultiplicativeExpression(source);\n }\n // 除法\n if (source[0].type === 'MultiplicativeExpression' && source[1] && source[1].type === '/') {\n let node = {\n type: 'MultiplicativeExpression',\n operator: '/',\n children: [],\n };\n node.children.push(source.shift());\n node.children.push(source.shift());\n node.children.push(source.shift());\n source.unshift(node);\n return MultiplicativeExpression(source);\n }\n\n if (source[0].type === 'MultiplicativeExpression') {\n return source[0];\n }\n\n return MultiplicativeExpression(source);\n}\n\nconsole.log(Expression(source));\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"好，这个就是整个 LL 语法分析的主要过程了。我们到了这里就成功的解析了一个四则运算的表达式。对，不容易但是我们终于完成了。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/ae/ae96ca354aebd9bd3378ac90d783cd67.gif","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"horizontalrule","attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"我是来自《","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"技术银河","attrs":{}},{"type":"text","text":"》的","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"三钻","attrs":{}},{"type":"text","text":"：\"学习是为了成长，成长是为了不退步。坚持才能成功，失败只是因为没有坚持。同学们加油哦！下期见！\"","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/f7/f7db8645b6fdfa85351bc5f5aeb79aeb.gif","alt":null,"title":"","style":[{"key":"width","value":"25%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"horizontalrule","attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/23/237db88ffb40799313e26780f79aad9e.gif","alt":null,"title":null,"style":null,"href":null,"fromPaste":true,"pastePass":false}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"博主开始在B站直播学习，欢迎过来《","attrs":{}},{"type":"link","attrs":{"href":"https://live.bilibili.com/22619211","title":""},"content":[{"type":"text","text":"直播间","attrs":{}}]},{"type":"text","text":"》一起学习。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"我们在这里互相监督，互相鼓励，互相努力走上人生学习之路，让学习改变我们生活！","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"学习的路上，很枯燥，很寂寞，但是希望这样可以给我们彼此带来多一点陪伴，多一点鼓励。我们一起加油吧！ (๑ •̀ㅂ•́)و","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"horizontalrule","attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"我是来自微信公众号《","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"技术银河","attrs":{}},{"type":"text","text":"》的","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"三钻","attrs":{}},{"type":"text","text":"，一位正在重塑知识的技术人。下期再见。","attrs":{}}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}}]}