我试图为sablecc编写一个minipython版本的规范文件(带有postfix /前缀增量和减量运算符),有些产品自然需要使用标识符,但是在解析过程中我遇到了这些冲突: / p>
shift/reduce conflict in state [stack: TPrint TIdentifier *] on TPlusPlus in {
[ PMultiplication = TIdentifier * ] followed by TPlusPlus (reduce),
[ PPostfix = TIdentifier * TPlusPlus ] (shift)
}
shift/reduce conflict in state [stack: TPrint TIdentifier *] on TMinusMinus in {
[ PMultiplication = TIdentifier * ] followed by TMinusMinus (reduce),
[ PPostfix = TIdentifier * TMinusMinus ] (shift)
}
shift/reduce conflict in state [stack: TPrint TIdentifier *] on TLPar in {
[ PFunctionCall = TIdentifier * TLPar PArglist TRPar ] (shift),
[ PFunctionCall = TIdentifier * TLPar TRPar ] (shift),
[ PMultiplication = TIdentifier * ] followed by TLPar (reduce)
}
shift/reduce conflict in state [stack: TPrint TIdentifier *] on TLBr in {
[ PExpression = TIdentifier * TLBr PExpression TRBr ] (shift),
[ PMultiplication = TIdentifier * ] followed by TLBr (reduce),
[ PPostfix = TIdentifier * TLBr PExpression TRBr TMinusMinus ] (shift),
[ PPostfix = TIdentifier * TLBr PExpression TRBr TPlusPlus ] (shift)
}
java.lang.RuntimeException:
我开始遵循该语言的给定bnf并得到了这个。 这是语法文件:
Productions
goal = {prgrm}program* ;
program = {func}function | {stmt}statement;
function = {func}def identifier l_par argument? r_par semi statement ;
argument = {arg} identifier assign_value? subsequent_arguments* ;
assign_value = {assign} eq value ;
subsequent_arguments = {more_args} comma identifier assign_value? ;
statement = {case1}tab* if comparison semi statement
| {case2}tab* while comparison semi statement
| {case3}tab* for [iterator]:identifier in [collection]:identifier semi statement
| {case4}tab* return expression
| {case5}tab* print expression more_expressions
| {simple_equals}tab* identifier eq expression
| {add_equals}tab* identifier add_eq expression
| {minus_equals}tab* identifier sub_eq expression
| {div_equals}tab* identifier div_eq expression
| {case7}tab* identifier l_br [exp1]:expression r_br eq [exp2]:expression
| {case8}tab* function_call;
comparison = {less_than} comparison less relation
| {greater_than} comparison great relation
| {rel} relation;
relation = {relational_value} relational_value
| {logic_not_equals} relation logic_neq relational_value
| {logic_equals} relation logic_equals relational_value;
relational_value = {expression_value} expression_value
| {true} true
| {false} false;
expression = {case1} arithmetic_expression
| {case2} prefix
| {case4} identifier l_br expression r_br
| {case9} l_br more_values r_br;
more_expressions = {more_exp} expression subsequent_expressions*;
subsequent_expressions = {more_exp} comma expression;
arithmetic_expression = {plus} arithmetic_expression plus multiplication
| {minus} arithmetic_expression minus multiplication
| {multiplication} multiplication ;
multiplication = {expression_value} expression_value
| {div} multiplication div expression_value
| {mult} multiplication mult expression_value;
expression_value = {exp} l_par expression r_par
| {function_call} function_call
| {value} value
| {identifier} identifier ;
prefix = {pre_increment} plus_plus prepost_operand
| {pre_decrement} minus_minus prepost_operand
| {postfix} postfix;
postfix = {post_increment} prepost_operand plus_plus
| {post_decrement} prepost_operand minus_minus;
prepost_operand = {value} identifier l_br expression r_br
| {identifier} identifier;
function_call = {args} identifier l_par arglist? r_par;
arglist = {arglist} more_expressions ;
value = {number} number
| {string} string ;
more_values = {more_values} value subsequent_values* ;
subsequent_values = comma value ;
number = {int} numeral
| {float} float_numeral ;
其中标识符当然是一个标记,可以找到的有问题的产品是function_call,prepost_operand,expression_value。 我实验性地删除了前缀/后缀和prepost_operand以查看冲突是否至少会改变一点,但这只是留下了最后两个冲突。 有没有什么方法可以解决这些冲突而不会更改语法,或者我走错了路?
答案 0 :(得分:1)
问题在于生产的右侧是:
print expression more_expressions
more_expressions
匹配表达式列表(所以它可能应该被称为expression_list
以减少混淆)。规则中连续两个expression
显然不明确(如果您有两个表达式,1+1+1
1+1
后跟+1
或1
后跟{ {1}}?)。你想要的只是
+1+1