32语言和文法 无二义的文法 stmt→) matched stmt J unmatched stmt matched stmt>if expr then matched stmt else matched stmt l other unmatched stmt->if expr then stmt I if expr then matched stmt else unmatched stmt3.2 语言和文法 • 无二义的文法 stmt → matched _stmt | unmatched_stmt matched_stmt → if expr then matched_stmt else matched_stmt | other unmatched_stmt → if expr then stmt | if expr then matched_stmt else unmatched_stmt