perl – 使用Parse :: RecDescent

我运行你的程序,但添加了以下行：

use strict;
use warnings; # you should always have strict and warnings on
$::RD_HINT = 1; # Parse::RecDescent hints
$::RD_TRACE = 1; # Parse::RecDescent trace

并获得此调试输出：

1|beginning |>>Matched terminal<< (return value:   |
  |          |[@Book{])                             |
 1|beginning |                                      |"press,n author = "Press,|          |                                      |W. and Teutolsky,S. and
  |          |                                      |Vetterling,W. and Flannery
  |          |                                      |B.",n title = "Numerical
  |          |                                      |{R}ecipes in {C}: The {A}rt
  |          |                                      |of {S}cientific
  |          |                                      |{C}omputing",n year =
  |          |                                      |2007,n publisher =
  |          |                                      |"Cambridge University
  |          |                                      |Press"n}n"
 1|beginning |Trying subrule: [keyword]             |
 2| keyword  |Trying rule: [keyword]                |
 2| keyword  |Trying production: [/[a-zA-Z]+/ ',']  |
 2| keyword  |Trying terminal: [/[a-zA-Z]+/]        |
 2| keyword  |>>Matched terminal<< (return value:   |
  |          |[press])                              |
 2| keyword  |                                      |",W. and
  |          |                                      |Teutolsky,n publisher =
  |          |                                      |"Cambridge University
  |          |                                      |Press"n}n"
 2| keyword  |Trying terminal: [',']                |
 2| keyword  |>>Matched terminal<< (return value:   |
  |          |[,])                                  |
 2| keyword  |                                      |"n author = "Press,n publisher =
  |          |                                      |"Cambridge University
  |          |                                      |Press"n}n"
 2| keyword  |Trying action                         |
 1|beginning |>>Matched subrule: [keyword]<< (return|
  |          |value: [    <keyword>press</keyword> ]|
 1|beginning |                                      |"press,n publisher =
  |          |                                      |"Cambridge University
  |          |                                      |Press"n}n"
 1|beginning |Trying subrule: [fields]              |
 2|  fields  |Trying rule: [fields]                 |
 2|  fields  |Trying production: [one ',' two ','   |
  |          |three ',' four]                       |
 2|  fields  |Trying subrule: [one]                 |
 3|   one    |Trying rule: [one]                    |
 3|   one    |Trying production: ['author' '=' '"' |
  |          |/[a-zA-Zs.,{}:]+/ '"']           |
 3|   one    |Trying terminal: ['author']           |
 3|   one    |<<Didn't match terminal>>             |
 3|   one    |<<Didn't match rule>>                 |
 2|  fields  |<<Didn't match subrule: [one]>>       |
 2|  fields  |<<Didn't match rule>>                 |
 1|beginning |<<Didn't match subrule: [fields]>>    |
 1|beginning |<<Didn't match rule>>                 |
Bad text! at parser.pl line 32,<$in> line 6.

这表明它已经陷入第一个阶段,并且按下,将被放回输入流.这是因为你使用return而不是$return =作为Parse :: RecDescent手册says you should.

此外,一旦分配给$return变量,就不能再返回列表,并且必须手动将字符串连接在一起.

这是最终结果：

use strict;
use warnings;
use Parse::RecDescent;

open(my $in,"parsing.txt")  or die "Can't open parsing.txt: $!";

my $text;
while (<$in>) {
    $text .= $_;
}

print $text;

my $grammar = q {
    beginning: "@Book{" keyword fields /s*}s*/           { print "<book>n","                            { $return = "    <keyword>$item[1]</keyword>n"; }
    fields: one /,s*/ two /,s*/ three /,s*/ four               { $return = $item[1].$item[3].$item[5].$item[7]; }
    one: "author" "=" """ /[a-zA-Zs.,{}:]+/ """ {   $item[4] =~ s/sands/+/g;
                                                            $return =  "    <author>$item[4]</author>n"; }
    two: "title" "=" """ /[a-zA-Zs.,{}:]+/ """  {   $item[4] =~ s/sands/+/g;
                                                            $return =  "    <title>$item[4]</title>n"; }
    three: "year" "=" /[0-2][0-9][0-9][0-9]/            {   $return = "    <year>$item[3]</year>n"; }
    four: "publisher" "=" """ /[a-zA-Zs.,{}:]+/ """ 
                                                        {   $item[4] =~ s/sands/+/g;
                                                            $return = "    <publisher>$item[4]</publisher>n"; }
};

my $parser = new Parse::RecDescent($grammar) or die ("Bad grammar!");
defined $parser->beginning($text) or die ("Bad text!");