ddmyx/objects/oTyper/Step_0.gml

// oTyper Step Event
if active != _prev_active
{
    type_direction = active ? 1 : -1;
    is_done        = false;
    char_timer     = 0;
    _prev_active   = active;
}

if is_done exit;

char_timer++;
var _delay = (type_direction == 1) ? char_delay : char_delay_out;
if char_timer < _delay exit;
char_timer = 0;

char_index = clamp(char_index + type_direction, 0, string_length(text_full));
text_shown = string_copy(text_full, 1, char_index);
is_done    = (type_direction == 1) ? (char_index >= string_length(text_full))
                                   : (char_index <= 0);