Add ability to set random seed

[peddie]

Thanks for this handy library. We're using it as part of a CI process which we'd like to be deterministic in the sense that if I make some changes that don't affect a component that's property-tested in the CI process, a failure of a property test shouldn't cause the CI system to reject my changes. To do this, we'd like to be able to set a fixed seed in this CI process (rather than deriving it from IO as tasty-hedgehog currently does) and vary the seed as part of a separate testing process when we want to search for existing bugs that could be but haven't been found.

A good way to pass a fixed seed would be as an environment variable. A command-line argument could also work.

cc @ghorn

[ghorn]

A command-line argument would be significantly more convenient for our build system at work.

[mbg]

Hi @peddie and @ghorn. Sorry that there hasn't been a response to this issue. I just wanted to check if you still need something like this? I note that hedgehog itself includes an option for this as of version 1.1.1 by setting an environment variable named HEDGEHOG_SEED. There is also the existing HedgehogReplay option in this library.

[peddie]

Thanks for checking in. This is not urgently blocking anything, and the HEDGEHOG_SEED workaround works, but it would still be more convenient to be able to pass a command-line argument.