public async Task <decimal> Calculate()
{
var(initiator, commandStack) = _commandLexer
.CreateExecutableStack(
_commandParser.ParseInstructions(
await _commandExtractor.Extract().ConfigureAwait(false)));
decimal result = initiator;
while (commandStack.TryPop(out var instruction))
{
var(command, value) = instruction;
result = _operators[command].Invoke(result, value);
}
return(result);
}