PEG.JS example

gistfile1.txt

start =
    comma

comma = left:additive "," right:comma
        { return {tag: ",", left, right}; }   / additive

additive =
    left:multiplicative "+" right:additive
        { return {tag: "+", left, right}; }  / multiplicative

multiplicative =
    left:division "*" right:multiplicative
        { return {tag: "*", left, right}; }  / division

division =
    left:primary "/" right:division
        { return {tag: "/", left, right}; } / primary

primary =
    integer / "(" a:comma ")"
      { return a; }

integer =
    digits:[0-9]+
        { return parseInt(digits.join(""), 10); }