goto line1;

input:    { my (        $c) = @_; ...; @_ = ($value ); goto($c); }
process1: { my ($input, $c) = @_; ...; @_ = ($result); goto($c); }
process2: { my ($input, $c) = @_; ...; @_ = ($result); goto($c); }
output:   { my ($result   ) = @_; ...;                           }

line1: { push(@_, 'line2'); goto input;    }
line2: { push(@_, 'line3'); goto process1; }
line3: { push(@_, 'line4'); goto process2; }
line4: {                    goto output;   }