我的antlr解析器语法中有一个左递归错误
我发现了错误我的antlr解析器语法中有一个左递归错误,antlr,grammar,antlr3,left-recursion,ambiguous-grammar,Antlr,Grammar,Antlr3,Left Recursion,Ambiguous Grammar,我发现了错误 [fatal] rule statement has non-LL(*) decision due to recursive rule invocations reachable from alts 6,7. Resolve by left-factoring or using syntactic predicates or using backtrack=true option. 我不知道我的语法的哪一部分出现了这个错误。alt 3,4还有一个相同的错误 p
[fatal] rule statement has non-LL(*) decision due to recursive rule invocations reachable from alts 6,7. Resolve by left-factoring or using syntactic predicates or using backtrack=true option.
我不知道我的语法的哪一部分出现了这个错误。alt 3,4还有一个相同的错误
parser grammar syn1;
options {
tokenVocab = lex1;
buildAST=true;
}
program :
statements
;
statements :
statement ( SEMICOLON^ statement )*
;
statement :
variable ASSIGN^ exp
| SKIP
| IF^ boolexp THEN statement ELSE statement
| WHILE^ boolexp DO statement
| READ^ OPENPAREN! variable CLOSEPAREN!
| WRITE^ OPENPAREN! exp CLOSEPAREN!
| WRITE^ OPENPAREN! boolexp CLOSEPAREN!
| WRITE^ OPENPAREN! STRING CLOSEPAREN!
| WRITELN
| OPENPAREN! statements CLOSEPAREN!
;
boolexp :
boolterm ( AND^ boolterm )*
;
boolterm :
NOT^ bool
| bool
;
bool :
TRUE
| FALSE
| exp EQUALS^ exp
| exp LESSEQUALS^ exp
| OPENPAREN! boolexp CLOSEPAREN!
;
exp :
term (( ADD | SUBTRACT )^ term )*
;
term :
factor ( MULTIPLY^ factor ) *
;
factor :
variable
| INTNUM
| OPENPAREN exp CLOSEPAREN
;
variable :
IDENTIFIERS
;
我不知道哪一部分需要重新排列以删除左递归,如果有人能指出它,我将不胜感激。问题似乎在于以下两种选择:
| WRITE^ OPENPAREN! exp CLOSEPAREN!
| WRITE^ OPENPAREN! boolexp CLOSEPAREN!
导致递归的示例输入,即我可以重复最后一部分任意多次,并且它仍然是这两个规则的有效前缀:
写
写入myVar+myVar+。。。
在这两种情况下,只有看到+、-、*、和、非或,您才能知道选择哪个选项