语法分析器（syntax analyzer） Perl实现

    #!/usr/bin/perl
    
    use strict;   # parse.pl - inputs lex, outputs flattened ast
    use warnings; # http://www.rosettacode.org/wiki/Compiler/syntax_analyzer
    
    my $h = qr/\G\s*\d+\s+\d+\s+/;  # header of each line
    
    sub error { die "*** Expected @_ at " . (/\G(.*\n)/ ?
      $1 =~ s/^\s*(\d+)\s+(\d+)\s+/line $1 character $2 got /r : "EOF\n") }
    
    sub want { /$h \Q$_[1]\E.*\n/gcx ? shift : error "'$_[1]'" }
    
    local $_ = join '', <>;
    print want stmtlist(), 'End_of_input';
    
    sub stmtlist
      {
      /(?=$h (RightBrace|End_of_inp