Programming Exercise: Dice

A short exercise for the reader: come up with a domain specific language for rolling dice. This is a recurring mechanic in Rogue-likes.

Exercise 1. The conventional notation in Dungeons and Dragons is to write "mdn + k" (where "+ k" is optional) to roll m separate n-sided dice, sum them together, then add k to the result and return it. Write a function to accept a string of this form.

What happens when m is not a positive integer? When n is not a positive integer?

Exercise 2. In Dungeons and Dragons, when creating a character, you roll 4d6 but take the highest 3 values. How would you extend the domain language to include this situation?

The source for these exercises are the original Rogue-likes had a function which rolled dice based on a domain specific language, and this idea was picked up by Troll.