dmit

  class Bean {
    private boolean sprouted;

    public void sprout() {
      this.sprouted = true;
      // ...
    }
  }

  data Bean = Dormant | Sprouted
  
  sprout :: Bean -> Bean
  sprout Dormant = Sprouted
  sprout Sprouted = -- aw, beans, we could have modeled
                    -- this state as impossible to construct,
                    -- but you chose runtime checks, so
                    -- here we are.