Javascript 使用PEG.js进行解析计算
我正在尝试使用peg.js库解析数学表达式。 我输入了以下语法:Javascript 使用PEG.js进行解析计算,javascript,parsing,Javascript,Parsing,我正在尝试使用peg.js库解析数学表达式。 我输入了以下语法: start = any additive = left:primary "+" right:any { return left + right; } multiplicative = left:primary "*" right:any { return left * right; } any = multiplicative / additive / primary pri
start
= any
additive
= left:primary "+" right:any { return left + right; }
multiplicative
= left:primary "*" right:any { return left * right; }
any
= multiplicative
/ additive
/ primary
primary
= float
/ integer
/ "(" any:any ")" { return any; }
/ "" { return 0; }
float "float"
= left:[0-9]+ "." right:[0-9]+ { return parseFloat(left.join("") + "." + right.join("")); }
integer "integer"
= digits:[0-9]+ { return parseInt(digits.join(""), 10); }
但当我试图计算时:
3*5+1
我得到了18
我想下面的代码就是你想要的
诀窍是让最弱的运算符(+)有一个引用乘法规则的规则,以便在乘法匹配之前加法不能发生,而在主表达式匹配之前加法也不能发生
start
= any
any
= additive
additive
= left:multiplicative "+" right:additive { return left + right; }
/ multiplicative
multiplicative
= left:primary "*" right:multiplicative { return left * right; }
/ primary
primary
= float
/ integer
/ "(" any:any ")" { return any; }
/ "" { return 0; }
float "float"
= left:[0-9]+ "." right:[0-9]+ { return parseFloat(left.join("") + "." + right.join("")); }
integer "integer"
= digits:[0-9]+ { return parseInt(digits.join(""), 10); }
您已经创建了一个正确的关联语法,并且使乘法和加法具有相同的优先级。如何使运算符具有适当的优先级?您需要另一个非终端“层”,以便将乘法解析为比加法操作数更低级别的组。