我正在将语法从 LALR 翻译为 ANTLR,但在翻译这一规则时遇到了麻烦,即分段表达式。
附上示例语法:
grammar Test;
options {
language = Java;
output = AST;
}
parse : expression ';'
;
expression : binaryExpression
| piecesExpression
;
binaryExpression : addingExpression (('=='|'!='|'<='|'>='|'>'|'<') addingExpression)*
;
addingExpression : multiplyingExpression (('+'|'-') multiplyingExpression)*
;
multiplyingExpression : unaryExpression
(('*'|'/') unaryExpression)*
;
unaryExpression: ('!'|'-')* primitiveElement;
primitiveElement : literalExpression
| id
| '(' expression ')'
;
literalExpression : INT
;
id : IDENTIFIER
;
piecesExpression : 'piecewise' '{' piece expression '}' ('(' expression ',' expression ')')? expression?
;
piece : expression '->' expression ';' (expression '->' expression ';')*
;
// L E X I C A L R U L E S
INT : DIGITS ;
IDENTIFIER : LETTER (LETTER | DIGIT)*;
WS : ( ' '
| '\t'
| '\r'
| '\n'
) {$channel=HIDDEN;}
;
fragment LETTER : ('a'..'z' | 'A'..'Z' | '_') ;
fragment DIGITS: DIGIT+;
fragment DIGIT : '0'..'9';
ANTLR v3.5 抱怨piecesExpression 规则。它有 2 个致命错误,我宁愿不使用回溯选项。
预期成绩:
piecewise {t -> s; t -> x; 100}
piecewise {t -> s; t -> x; 100} (0, x+1)
piecewise {t -> s; t -> x; 100} (0, x+1) y+5
piecesExpression 是如何捕捉到上述结果的呢?
提前致谢!