32语言和文法 325消除二义性 smt→ if expr then stmt if expr then stmt else stmt I other 句型: if expr then if expr then stmt else stmt 两个最左推导 stmt if expr then stmt if expr then if expr then stmt else stmt stmt if expr then stmt else stmt ifexpr then if expr then stmt else stmt3.2 语言和文法 3.2.5 消除二义性 stmt → if expr then stmt | if expr then stmt else stmt | other • 句型：if expr then if expr then stmt else stmt • 两个最左推导： stmt  if expr then stmt  if expr then if expr then stmt else stmt stmt  if expr then stmt else stmt  if expr then if expr then stmt else stmt