_D_e_t_e_r_m_i_n_e _t_h_e _M_a_c_h_i_n_e _R _i_s _R_u_n_n_i_n_g _O_n
	
	     machine()
	
	_D_e_s_c_r_i_p_t_i_o_n:
	
	     This function returns a string which specifies what
	     kind of environment R is being run in.
	
	_E_x_a_m_p_l_e_s:
	
	     if(machine() == "Macintosh")
	          cat("You are using a Macintosh computer\n")