32语言和文法 expr>expr+ term term term->term factorI factor factor→>idl(expr) erDi erpr term expr term term factor termterm factor term k factor id Ictor actor actor id id id id id id s id 分析树 分析树3.2 语言和文法 expr → expr + term | term term → term  factor | factor factor → id | (expr) expr id term factor id id term * term factor factor * expr expr + id factor term id id term * term factor factor id + id  id 分析树 id  id  id 分析树