astBinaryExpression(ast, retArr) {
    retArr.push('(');
    this.astGeneric(ast.left, retArr);
    retArr.push(ast.operator);
    this.astGeneric(ast.right, retArr);
    retArr.push(')');
    return retArr;
  }
@desc Parses the abstract syntax tree for *binary* expression
@param {Object} ast - the AST object to parse
@param {Array} retArr - return array string
@returns {Array} the append retArr