start = expression expression = atom / listatom / nestedlist validchar = [0-9a-zA-Z_?!+\-=@#$%^&*/.] atom = chars:validchar+ { return chars.join(""); } listatom = "(" space* natom:atom satom:spaceatom* space* ")" { if (satom && satom.length) { satom.unshift(natom); return satom; } else { return [natom]; } } nestedlist = "(" space* natom1:atom* satom1:spaceatom* space* latom1:listatom* space* ")" { var result = []; if (natom1 && natom1.length) { result = result.concat(natom1); } if (satom1 && satom1.length) { result = result.concat(satom1); } if (latom1 && latom1.length) { result = result.concat(latom1); } return result; } space = " " spaceatom = space natom:atom { return natom; }