如何在Jison中匹配零个或多个标记

Question

我正在用Jison编写一个简单的表达式解析器，允许在表达式中的二进制操作符后面跟随任意数量的换行符。这是我到目前为止的语法:

{
    "operators": [
        ["left", "+", "-"],
        ["left", "*", "/", "%"]
    ],
    "bnf": {
        "program": [
            ["statement EOF", "return $1;"]
        ],
        "statement": [
            ["expression newlines", "$$ = $1 + ';';"]
        ],
        "expression": [
            ["NUMBER",                           "$$ = yytext;"],
            ["expression + expression",          "$$ = $1 + ' + ' + $3;"],
            ["expression - expression",          "$$ = $1 + ' - ' + $3;"],
            ["expression * expression",          "$$ = $1 + ' * ' + $3;"],
            ["expression / expression",          "$$ = $1 + ' / ' + $3;"],
            ["expression % expression",          "$$ = $1 + ' % ' + $3;"],
            ["expression + newlines expression", "$$ = $1 + ' + ' + $4;"],
            ["expression - newlines expression", "$$ = $1 + ' - ' + $4;"],
            ["expression * newlines expression", "$$ = $1 + ' * ' + $4;"],
            ["expression / newlines expression", "$$ = $1 + ' / ' + $4;"],
            ["expression % newlines expression", "$$ = $1 + ' % ' + $4;"]
        ],
        "newlines": [
            ["NEWLINE",          ""],
            ["newlines NEWLINE", ""]
        ]
    }
}

正如你所看到的，我为每个二进制运算符写了两个规则。在我看来，那是非常多余的。我宁愿有一个匹配零个或多个NEWLINE代币(Kleene星号)的产品，而不是一个或多个代币(Kleene plus)。在杰森你会怎么做?

Answer 1

我使用Jison，忽略空白(包括换行)。

my %lex中的第一行是:

s+   /* ignore */

但是如果你不想的话，你可以不这样做。试试这样做:

"expression": [
            ["NUMBER",                           "$$ = yytext;"],
            ["expression + expression",          "$$ = $1 + ' + ' + $3;"],
            ["expression - expression",          "$$ = $1 + ' - ' + $3;"],
            ["expression * expression",          "$$ = $1 + ' * ' + $3;"],
            ["expression / expression",          "$$ = $1 + ' / ' + $3;"],
            ["expression % expression",          "$$ = $1 + ' % ' + $3;"],
            ["expression newlines",              "$$ = $1"],
            ["newlines expression",              "$$ = $2"]
        ],

这应该允许任意数量的新行在任何表达式之前/之后。