Question

我试图从第11章的Eloquent Javascript书中重现语言解析器。请参阅here。

当我尝试这样做时：

function parseExpression(program) {
  program = skipSpace(program);
  var match, expr;
  if (match = /^"([^"]*)"/.exec(program))
    expr = {type: "value", value: match[1]};
  else if (match = /^\d+\b/.exec(program))
    expr = {type: "value", value: Number(match[0])};
  else if (match = /^[^\s(),"]+/.exec(program))
    expr = {type: "word", name: match[0]};
  else
    throw new SyntaxError("Unexpected syntax: " + program);

  return parseApply(expr, program.slice(match[0].length));
}

我从SyntaxError: Unexpected end of input获得了一个非常奇怪的if。

然而，像if (str = 'my string')这样的虚拟分配工作完美。正则表达式正在搞乱这种行为吗？

编辑：我尝试使用控制台进行调试。这是我得到的：

$ node
> .load parser.js
> function parseExpression(program) {
...   program = skipSpace(program);
...   var match, expr;
...   if ((match = /^"([^"]*)"/.exec(program)))
SyntaxError: Unexpected end of input
    at Object.exports.createScript (vm.js:24:10)
    at REPLServer.defaultEval (repl.js:225:25)
    at bound (domain.js:287:14)
    at REPLServer.runBound [as eval] (domain.js:300:12)
    at REPLServer.<anonymous> (repl.js:417:12)
    at emitOne (events.js:82:20)
    at REPLServer.emit (events.js:169:7)
    at REPLServer.Interface._onLine (readline.js:210:10)
    at REPLServer.Interface._line (readline.js:549:8)
    at REPLServer.Interface._ttyWrite (readline.js:884:20)
>     expr = {type: "value", value: match[1]};
ReferenceError: match is not defined
    at repl:1:31
    at REPLServer.defaultEval (repl.js:252:27)
    at bound (domain.js:287:14)
    at REPLServer.runBound [as eval] (domain.js:300:12)
    at REPLServer.<anonymous> (repl.js:417:12)
    at emitOne (events.js:82:20)
    at REPLServer.emit (events.js:169:7)
    at REPLServer.Interface._onLine (readline.js:210:10)
    at REPLServer.Interface._line (readline.js:549:8)
    at REPLServer.Interface._ttyWrite (readline.js:884:20)
>   else if (match = /^\d+\b/.exec(program))
...     expr = {type: "value", value: Number(match[0])};
...   else if (match = /^[^\s(),"]+/.exec(program))
SyntaxError: Unexpected token else
    at Object.exports.createScript (vm.js:24:10)
    at REPLServer.defaultEval (repl.js:225:25)
    at bound (domain.js:287:14)
    at REPLServer.runBound [as eval] (domain.js:300:12)
    at REPLServer.<anonymous> (repl.js:417:12)
    at emitOne (events.js:82:20)
    at REPLServer.emit (events.js:169:7)
    at REPLServer.Interface._onLine (readline.js:210:10)
    at REPLServer.Interface._line (readline.js:549:8)
    at REPLServer.Interface._ttyWrite (readline.js:884:20)
>     expr = {type: "word", name: match[0]};
ReferenceError: match is not defined
    at repl:1:29
    at REPLServer.defaultEval (repl.js:252:27)
    at bound (domain.js:287:14)
    at REPLServer.runBound [as eval] (domain.js:300:12)
    at REPLServer.<anonymous> (repl.js:417:12)
    at emitOne (events.js:82:20)
    at REPLServer.emit (events.js:169:7)
    at REPLServer.Interface._onLine (readline.js:210:10)
    at REPLServer.Interface._line (readline.js:549:8)
    at REPLServer.Interface._ttyWrite (readline.js:884:20)
>   else
...     throw new SyntaxError("Unexpected syntax: " + program);
...   return parseApply(expr, program.slice(match[0].length));
... }

Answer 1

节点似乎在regexp中的"字符有问题。通过转义它们，函数可以正确解析。

function parseExpression(program) {
  program = skipSpace(program);
  var match, expr;
  if ((match = /^\"([^\"]*)\"/.exec(program)))
    expr = {type: "value", value: match[1]};
}

Answer 2

你的代码没有错：

C:\test>node -v
v5.7.0

C:\test>node
> .load parser.js
> function parseExpression(program) {
...   program = skipSpace(program);
...   var match, expr;
...   if (match = /^"([^"]*)"/.exec(program))
...     expr = {type: "value", value: match[1]};
...   else if (match = /^\d+\b/.exec(program))
...     expr = {type: "value", value: Number(match[0])};
...   else if (match = /^[^\s(),"]+/.exec(program))
...     expr = {type: "word", name: match[0]};
...   else
...     throw new SyntaxError("Unexpected syntax: " + program);
...
...   return parseApply(expr, program.slice(match[0].length));
... }
undefined
>

如果它对您不起作用，我说它会影响您的版本的Node错误（您不能确切地说出哪一个），也许#5113 repl cannot handle single quote in regex, when within a function）：

我得到了一个＆＃39; SyntaxError：意外的输入结束＆＃39;当我尝试在repl中输入以下内容
var someFunction = function(s) {
    s = s.replace(/'/g, '');
}
但是，s = s.replace(/'/g, '')本身在新行上是可以的。我做错了什么？

该错误已在Node/5.7.0修复。

Answer 3

尝试在Node v6.10.3上运行此代码时遇到了同样的问题。当我在正则表达式中转义引号时结束工作，正如其他人所说的那样。

同时分配和检查并具有良好的语法错误

3 个答案: