_C_o_n_t_r_o_l _F_l_o_w
	
	     if(cond) expr
	     if(cond) cons.expr  else  alt.expr
	     for(var in seq) expr
	     while(cond) expr
	     repeat expr
	     break
	     next
	
	_D_e_s_c_r_i_p_t_i_o_n:
	
	     These are the basic control-flow constructs of the R
	     language.  They function in much the same way as con-
	     trol statements in any algol-like language.
	
	_S_e_e _A_l_s_o:
	
	     ifelse, switch.
	
	_E_x_a_m_p_l_e_s:
	
	     for(i in 1:5) print(1:i)