code: func (c *Client) FormationList(appIdentity string, lr *ListRange) ([]Formation, error) {
  	req, err := c.NewRequest("GET", "/apps/"+appIdentity+"/formation", nil, nil)
  	if err != nil {
  		return nil, err
  	}
  
  	if lr != nil {
  		lr.SetHeader(req)
  	}
  
  	var formationsRes []Formation
  	return formationsRes, c.DoReq(req, &formationsRes)
  }
docs: // List process type formation
  //
  // appIdentity is the unique identifier of the Formation's App. lr is an
  // optional ListRange that sets the Range options for the paginated list of
  // results.