Custom shrinking?

[jeffometer]

Hello, great library, thank you. I am using this to generate a list of commands to find invalid combinations of commands. The simplest example is a serious of commands that cannot repeat any one command more than once.

The library works great at finding example sequences of commands that fail, but is unable to properly shrink. The ideal shrunken value would be a list of the same command twice. Instead I get the first full list of commands that triggered the fail. It appears the shrinker attempts to remove items from the list, but doesn't have a way to try different combinations of items in the list.

Is there already a built in way to do what I need, and if not, is it possible to build a custom shrinker myself?

Thanks!

[jeffometer]

I've learned that what I really want is a deterministic approach to generating commands, like https://github.com/alfert/propcheck. The discussion in #94 helped me come to this conclusion.