用PEG.js进行解析计算

Question

我试图使用peg.js库来解析数学表达式。我在在线peg.js中添加了以下语法：

start
    = any

additive
    = left:primary "+" right:any { return left + right; }

multiplicative
    = left:primary "*" right:any { return left * right; }

any
    = multiplicative
    / additive
    / primary

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); }

但是当我试图计算：3*5+1时，我得到了18

Answer 1

我想下面的代码就是你想要的。

诀窍是让最弱的操作符(+)有一个引用乘法规则的规则，以便在乘法匹配之后才能进行加法，而在主表达式匹配后才能进行加法。

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); }