source: vendor/perl/5.8.8/perl_keyword.pl

# How to generate the logic of the lookup table Perl_keyword() in toke.c

use Devel::Tokenizer::C 0.05;
use strict;
use warnings;

my @pos = qw(__DATA__ __END__ AUTOLOAD BEGIN CHECK DESTROY do delete defined
             END else eval elsif exists for format foreach grep goto glob INIT
             if last local m my map next no our pos print printf package
             prototype q qr qq qw qx redo return require s scalar sort split
             study sub tr tie tied use undef until untie unless while y);

# In 5.8.x there is no err
my @neg = qw(__FILE__ __LINE__ __PACKAGE__ and abs alarm atan2 accept bless
             bind binmode CORE cmp chr cos chop close chdir chomp chmod chown
             crypt chroot caller connect closedir continue die dump dbmopen
             dbmclose eq eof exp exit exec each endgrent endpwent
             endnetent endhostent endservent endprotoent fork fcntl flock
             fileno formline getppid getpgrp getpwent getpwnam getpwuid
             getpeername getprotoent getpriority getprotobyname
             getprotobynumber gethostbyname gethostbyaddr gethostent
             getnetbyname getnetbyaddr getnetent getservbyname getservbyport
             getservent getsockname getsockopt getgrent getgrnam getgrgid
             getlogin getc gt ge gmtime hex int index ioctl join keys kill lt
             le lc log link lock lstat length listen lcfirst localtime mkdir
             msgctl msgget msgrcv msgsnd ne not or ord oct open opendir pop
             push pack pipe quotemeta ref read rand recv rmdir reset rename
             rindex reverse readdir readlink readline readpipe rewinddir seek
             send semop select semctl semget setpgrp seekdir setpwent setgrent
             setnetent setsockopt sethostent setservent setpriority
             setprotoent shift shmctl shmget shmread shmwrite shutdown sin
             sleep socket socketpair sprintf splice sqrt srand stat substr
             system symlink syscall sysopen sysread sysseek syswrite tell time
             times telldir truncate uc utime umask unpack unlink unshift
             ucfirst values vec warn wait write waitpid wantarray x xor);

my %pos = map { ($_ => 1) } @pos;

my $t = Devel::Tokenizer::C->new( TokenFunc     => \&perl_keyword
                                , TokenString   => 'name'
                                , StringLength  => 'len'
                                , MergeSwitches => 1
                                );

$t->add_tokens(@pos, @neg, 'elseif');

my $switch = $t->generate(Indent => '  ');

print <<END;
/*
 *  The following code was generated by $0.
 */

I32
Perl_keyword (pTHX_ char *name, I32 len)
{
$switch
unknown:
  return 0;
}
END

sub perl_keyword
{
  my $k = shift;
  my $sign = $pos{$k} ? '' : '-';

  if ($k eq 'elseif') {
    return <<END;
if(ckWARN_d(WARN_SYNTAX))
  Perl_warner(aTHX_ packWARN(WARN_SYNTAX), "elseif should be elsif");
END
  }

  return <<END;
return ${sign}KEY_$k;
END
}