=for state_machine

START
  \n  -> {flush} START
  ws  -> START
 else -> DECL

DECL
   ;  -> {flush} START
   )  -> CLOSE

CLOSE
  {   -> {block=1} FUNC
 else -> DECL

FUNC
  {   -> {++block} FUNC
  }   -> { --block ? FUNC : END }

END
  ws  -> END
  \n  -> {save} START
 else -> {save} DECL

=end

    use enum qw( START DECL CLOSE FUNC END );

    my $state= START();
    my $part= '';
    while(  $code =~ m{
        \G(
          \n            # newline
        | [^\S\n]+      # horizontal whitespace
        | [a-z]\w*      # identifier
        | \d+           # digit string
        | "(?:[^\\"]+|\\[^\n])*"
        | '(?:[^\\']+|\\[^\n])*'
        | /\*.*?\*/     # C comment
        | //[^\n]*\n    # C++ comment
        | [^\w\s]       # punctuation mark
        )
      }xsg
    ) {
        my $token= $1;
        if(  START() == $state  ) {
            if(  $token eq "\n"  ) {
                $token= $part= '';
            } elsif(  $token =~ /\S/  ) {
                $state= DECL();
            }
        ...
        } elsif(  END() == $state  ) {
            if(  $token =~ /\S/  ) {
                push @func, $part;
                $part= '';
                ...
            }
        }
        $part .= $token;
    }