public Task <DiceRollResult> Roll(string expression)
{
var parser = DiceNotationParser.FromString(expression);
var visitor = new DiceNotationVisitor(_diceRng);
var expressionResult = visitor.VisitNotation(parser.notation());
var diceRollResult = new DiceRollResult(visitor.DiceRolls, expressionResult);
return(Task.FromResult(diceRollResult));
}