2

我正在尝试使用 Jison。

这是我的语法：

var grammar = {
lex:{
    rules:[
        ["\\s+",            ""],
        ["then",            "return 'newline';"],
        ["goto",            "return 'goto';"],
        ["http[^\\s]*",     "return 'url';"],
        ["search",          "return 'search';"],
        ["should_exist",    "return 'exist';"],
        //["#(.)*",           "return 'elementById';"],
        //["$",               "return 'EOF';"]
    ]
},
bnf:{
    lines:[
        ['lines line',          "console.log('big expression is ',$3);  return ['l2',$1, $2];"],
        ['line',                "console.log('expression is ',$1); return ['l1',$1]"],
    ],
    line:[
        ["line newline",        "console.log('line newline', $1); $$ = $1"],
        ["goto url",            "console.log('goto', $2); $$ = {cmd:'goto', url: $2 } "],
        ["elementById exist",   "$$ = {cmd:'assert', elId: $1} "]
    ]
}
};

当我尝试解析时，goto http://www.google.com then goto http://www.bing.com我只会被[ 'l1', { cmd: 'goto', url: 'http://www.google.com' } ]返回。

我期望同时返回两个 goto 命令。

对我弄清楚我的语法有什么帮助吗？

4

2 回答 2

3

您的代码中的主要问题是过早使用return. 使用将在此处return结束解析。因此，如果您在不打算终止解析的规则中使用它，那么您就有麻烦了。我喜欢有一个规则，它是整个系统的入口点，它的工作只是用合理的东西来调用。return

这里有一些更像你想要的东西。我没有改变任何东西lex。

    bnf:{
        top: [
            ['lines', "console.log('top is ', $1);  return $1;"]
        ],
        lines:[
            ['lines line',          "console.log('big expression is ', $1);  $$ = ['l2', $1, $2];"],
            ['line',                "console.log('expression is ',$1); $$ = ['l1',$1]"],
        ],
        line:[
            ["line newline",        "console.log('line newline', $1); $$ = $1"],
            ["goto url",            "console.log('goto', $2); $$ = {cmd:'goto', url: $2 } "],
            ["elementById exist",   "$$ = {cmd:'assert', elId: $1} "]
        ]
    }

我得到的输出是：

goto http://www.google.com
line newline { cmd: 'goto', url: 'http://www.google.com' }
expression is  { cmd: 'goto', url: 'http://www.google.com' }
goto http://www.bing.com
big expression is  [ 'l1', { cmd: 'goto', url: 'http://www.google.com' } ]
top is  [ 'l2',
  [ 'l1', { cmd: 'goto', url: 'http://www.google.com' } ],
  { cmd: 'goto', url: 'http://www.bing.com' } ]

这是您最初拥有的和我的建议之间的差异：

--- original.js 2014-02-23 08:10:37.605989877 -0500
+++ parser.js   2014-02-23 08:35:06.674952990 -0500
@@ -14,9 +14,12 @@
         ]
     },
     bnf:{
+        top: [
+            ['lines', "console.log('top is ', $1);  return $1;"]
+        ],
         lines:[
-            ['lines line',          "console.log('big expression is ',$3);  return ['l2',$1, $2];"],
-            ['line',                "console.log('expression is ',$1); return ['l1',$1]"],
+            ['lines line',          "console.log('big expression is ', $1);  $$ = ['l2', $1, $2];"],
+            ['line',                "console.log('expression is ',$1); $$ = ['l1',$1]"],
         ],
         line:[
             ["line newline",        "console.log('line newline', $1); $$ = $1"],
于 2014-02-23T13:42:40.117 回答
1

我会反对您为此目的需要一个成熟的解析器。例如，您可以简单地使用词法分析器和手写递归下降解析器来做同样的事情：

var lexer = new Lexer;

lexer.addRule(/\s+/, function () {
    // skip whitespace
});

lexer.addRule(/then|goto|search/, function (lexeme) {
    return lexeme.toUpperCase();
});

lexer.addRule(/https?:\/\/[^\s]+/, function (lexeme) {
    this.yytext = lexeme;
    return "URL";
});

lexer.addRule(/$/, function () {
    return "EOF";
});

现在我们有了一个词法分析器，我们将创建递归下降解析器：

function parse(input) {
    lexer.setInput(input);
    return statement();
}

function statement() {
    var condition = command();
    match("THEN");
    var branch = command();
    match("EOF");

    return {
        condition: condition,
        branch: branch
    };
}

function command() {
    match("GOTO");
    var url = match("URL");

    return {
        command: "GOTO",
        url: url
    };
}

function match(expected) {
    var token = lexer.lex();
    if (token === expected) return lexer.yytext;
    else throw new Error("Unexpected token: " + token);
}

现在您需要做的就是调用parse：

var output = parse("goto http://www.google.com/ then goto http://www.bing.com/");

alert(JSON.stringify(output, null, 4));

亲自查看演示：http: //jsfiddle.net/r4RH2/1/

于 2014-02-23T05:45:49.570 回答