grammar - 如何引用语法中先前匹配的项目？

Question

我正在尝试解析 BibTeX 作者字段，并将其拆分为单独的作者。这将帮助我重写每个作者的姓名首字母。这是一个最小的例子:

use v6;

my $str = '{Rockhold, Mark L and Yarwood, RR and Selker, John S}';

grammar BibTexAuthor {
    token TOP {
        <all-text> 
    }
    token all-text {
        '{' <authors> '}' 
    }
    token authors { 
        [<author> [' and ' || <?before '}'>]]+
    }
    token author {
        [<-[\s}]> || [' ' <!before 'and '>]]+
    }
}

class BibTexAuthor-actions {
    method TOP($/) {
        say $/;
        print "First author = ";
        say $<author>.made[0];
        make $/.Str;
    }
    method all-text($/) {
        make $/.Str;
    }
    method authors($/) {
        make $/.Str;
    }
    method author($/) {
        make $/.Str;
    }
}
my $res = BibTexAuthor.parse( $str, actions => BibTexAuthor-actions.new).made;

输出:

｢{Rockhold, Mark L and Yarwood, RR and Selker, John S}｣
 all-text => ｢{Rockhold, Mark L and Yarwood, RR and Selker, John S}｣
  authors => ｢Rockhold, Mark L and Yarwood, RR and Selker, John S｣
   author => ｢Rockhold, Mark L｣
   author => ｢Yarwood, RR｣
   author => ｢Selker, John S｣
First author = Nil

为什么我无法在 TOP 方法中提取第一作者？

Answer 1

Why am I not able to extract the first author in the TOP method?

因为您并没有真正在操作方法中提取任何数据。您所做的只是将匹配的字符串附加到 $/.made 中，这实际上并不是您最终想要的数据。

如果您最终希望有不同的作者，您应该在 authors 操作方法中创建一个作者数组。例如:

use v6;

my $str = '{Rockhold, Mark L and Yarwood, RR and Selker, John S}';

grammar BibTexAuthor {
    token TOP {
        <all-text> 
    }
    token all-text {
        '{' <authors> '}' 
    }
    token authors { 
        [<author> [' and ' || <?before '}'>]]+
    }
    token author {
        [<-[\s}]> || [' ' <!before 'and '>]]+
    }
}

class BibTexAuthor-actions {
    method TOP($/) {
        make { authors => $<all-text>.made };
    }
    method all-text($/) {
        make $/<authors>.made;
    }
    method authors($/) {
        make $/<author>».made;
    }
    method author($/) {
        make $/.Str;
    }
}
my $res = BibTexAuthor.parse( $str, actions => BibTexAuthor-actions.new).made;

say $res.perl;

打印

${:authors($["Rockhold, Mark L", "Yarwood, RR", "Selker, John S"])}

所以现在顶级匹配的 .made 是一个哈希，其中 authors 键保存一个数组。如果您想访问第一作者，您现在可以说

say $res<authors>[0];

获取Rockhold，Mark L