Perl 6 规则中 .parse 锚点还是 :sigspace 首先？

我有两个问题。我表现出的行为是否正确？如果是，它是否记录在某处？

我在玩语法TOP方法。宣布为rule，它意味着字符串的开头和结尾锚点以及:sigspace:

grammar Number {
    rule TOP { \d+ }
    }

my @strings = '137', '137 ', ' 137 ';

for @strings -> $string {
    my $result = Number.parse( $string );
    given $result {
        when Match { put "<$string> worked!" }
        when Any   { put "<$string> failed!" }
        }
    }

如果没有空格或只有尾随空格，则字符串将被解析。由于前导空格，它会失败：

<137> worked!
<137 > worked!
< 137 > failed!

我想这意味着rule正在申请:sigspace首先是锚点，然后是锚点：

grammar Foo {
    regex TOP { ^ :sigspace \d+ $ }
    }

我期待一个rule允许前导空格，如果你改变顺序就会发生这种情况：

grammar Foo {
    regex TOP { :sigspace ^  \d+ $ }
    }

我可以添加一个显式标记rule对于字符串的开头：

grammar Number {
    rule TOP { ^ \d+ }
    }

现在一切正常：

<137> worked!
<137 > worked!
< 137 > worked!

我没有任何理由认为应该是其中一种方式。这语法文档 https://docs.perl6.org/language/grammars说发生了两件事，但文档没有说明这些效果适用的顺序：

请注意，如果您使用 .parse 方法进行解析，则标记 TOP 会自动锚定

and

当使用规则而不是标记时，原子后面的任何空格都会变成对 ws 的非捕获调用。

我认为答案是该规则实际上并不是以模式意义为基础的。就是这样.parse作品。光标必须从位置 0 开始，到字符串中的最后一个位置结束。这是模式之外的东西。

该行为是有意为之的，并且是这些语言功能的顶峰：

• Sigspace 忽略第一个原子之前的空格。

  From the design docs¹ (S05: Regexes and Rules, line 348 http://design.perl6.org/S05.html#line_348, emphasis added):

  The new :s (:sigspace) modifier causes certain whitespace sequences to be considered "significant"; they are replaced by a whitespace matching rule, . Only whitespace sequences immediately following a matching construct (atom, quantified atom, or assertion) are eligible. Initial whitespace is ignored at the front of any regex, to make it easy to write rules that can participate in longest-token-matching alternations. Trailing space inside the regex delimiters is significant.

  这意味着：

  
  
  rule TOP { \d+ }
                ^-------- <.ws> automatically inserted
  
  rule TOP { ^ \d+ $ }
              ^---^-^---- <.ws> automatically inserted
    

• 正则表达式是具有词法作用域的一流编译代码。

  正则表达式/规则不是一个稍后可能会连接字符以更改其行为的字符串。它是一个独立的例程，在编译时进行解析并确定其行为。

  Regex modifiers like :sigspace, including the one implicitly added by the rule keyword, apply only to their lexical scope - i.e. to the fragment of source code they appear in at compile time. S05, line 629 http://design.perl6.org/S05.html#line_629¹:

  The :i, :m, :r, :s, :dba, :Perl5, and Unicode-level modifiers can be placed inside the regex (and are lexically scoped)

• 的锚定rule TOP在运行时完成.parse.

  S05, line 4423 http://design.perl6.org/S05.html#line_4423¹:

  The .parse and .parsefile methods anchor to the beginning and ending of the text, and fail if the end of text is not reached. (The TOP rule can check against $ itself if it wishes to produce its own error message.)

  IE。锚定到字符串的开头并不是规则所固有的TOP，并且不影响词法范围TOP被解析和编译。当方法完成时.parse叫做。

  必须是这样，因为相同的语法可以使用不同的起始规则，而不是TOP, using .parse(..., rule => ...).

所以当你写的时候

rule TOP { \d+ }

它被编译为

regex TOP { :r \d+ <.ws> }

而当你.parse该语法，它有效地调用正则表达式代码^ <TOP> $，锚点不属于TOP的词法范围，而不是仅仅calls例行公事TOP。组合的行为就像规则一样TOP被写为：

regex TOP { ^ [:r :s \d+] $ }

^{1) The design docs are in general not to be taken as gospel for what is or isn't part of the Perl 6 language, but S05 is pretty accurate in that regard, except that it mentions some features that haven't been implemented yet but are planned. Anyone who wants to truly grok the intricacies of Perl 6 regexes/grammars, is IMO well served by reading the full S05 from top to bottom at least once.}