我写了一个语法,但得到了一个左递归错误.
grammar Lang;
options
{
output = AST;
language = C;
ASTLabelType= pANTLR3_BASE_TREE;
backtrack = true;
}
start : primary_expression+
;
primary_expression
: '{' expression '}'
| expression ',' expression
;
expression
: logical_or_expression
| logical_or_expression '?' expression ':' expression
| logical_or_expression '?' ':' expression
| logical_or_expression '?' expression
;
logical_or_expression
: logical_and_expression
| logical_and_expression '|' logical_or_expression
;
logical_and_expression
: primary_expression
| primary_expression '&' logical_and_expression
;
我收到以下错误:
[12:41:35] error(210): The following sets of rules are mutually left-recursive [primary_expression, logical_and_expression, logical_or_expression, expression]
[12:41:35] Aborting because the following rules are mutually left-recursive:
[[Lang.primary_expression,index=2,line=19], [Lang.logical_and_expression,index=5,line=36], [Lang.logical_or_expression,index=4,line=31], [Lang.expression,index=3,line=24]]
纠正了语法
grammar Lang;
options
{
// Note that in the C implementation, all implementations of trees and
// adaptors pass around pANTLR3_BASE_TREE, which contains a super pointer
// to your own implementation of a tree node and tree and so on. Hence
// the node type is ALWAYS pANTLR3_BASE_TREE and there is no need to define
// the type (the definition is silently ignored if you leave it there)
//
//output = AST;
language = C;
//ASTLabelType= pANTLR3_BASE_TREE;
backtrack = true;
}
start : primary_expression+
;
primary_expression
: '{' expression '}'
| expression ',' expression
;
expression
: logical_or_expression
| logical_or_expression '?' expression ':' expression
| logical_or_expression '?' ':' expression
| logical_or_expression '?' expression
;
logical_or_expression
: logical_and_expression
| logical_and_expression '|' logical_or_expression
;
logical_and_expression
: STRING
| STRING '&' logical_and_expression
;
/* We're going to ignore all white space characters */
WS
: (' ' | '\t' | '\r'| '\n') {$channel=HIDDEN;}
;
STRING
: ('a'..'z' | 'A'..'Z' | '0'..'9' | '_')+
;
最佳答案 Antlr 4可以处理直接左递归,但不能处理间接左递归.在第一种情况下,“primary_expression”和“logical_and_expression:primary_expression …”形成间接左递归.但是现在antlr4无法生成’c’代码.
grammar test3;
options
{
language = Java;
}
start :
expression+
;
expression :
primary_expression
| expression '&' expression
| expression '|' expression
| expression '?' expression ':' expression
| expression '?' expression
| expression '?' ':' expression
| expression ',' expression
| '{' expression '}'
;
primary_expression : // variable or constant definition, such as
VARIABLE
| NUMBER
;
VARIABLE :
('A'..'Z')+
;
NUMBER :
('0'..'9') +
;