This is the key sentence:

> The key insight of the Hypothesis library is that instead of shrinking generated values, we instead shrink the samples produced by the PRNG.

Hedgehog loses shrink information when you do a monadic bind (Gen a -> (a -> Gen b) -> Gen b). Hypothesis parses values out of the stream of data generated by the PRNG, so when it "binds", you are still just consuming off that stream of random numbers, and you can shrink the stream to shrink the generated values.

Here is a talk that applies the Hypothesis idea to test C++: https://www.youtube.com/watch?v=C6joICx1XMY . Discussion of PBT implementation approaches begins at 6:30.