code: def p_statement_if_then_endif(p):
      
      cond_ = p[1]
      stat_ = p[2]
      endif_ = p[3]
      p[0] = make_sentence('IF', cond_, make_block(stat_, endif_), lineno=p.lineno(1))
docs: statement : if_then_part statements_co endif
                    | if_then_part co_statements_co endif