## Summary

What does this pull request do?

**To do:**

If this pull request is a work-in-progress, add a checklist here of
the remaining tasks so it's clear what still needs to be done.

**Related issues:**

If this pull request is related to any other issues, list them here.


## Checklist

**If this is fixing a bug or adding a feature:**

- [ ] Add new tests to dejafu-tests

**If this is removing an unsupported GHC version:**

- [ ] Bump the lower bound on `base`
- [ ] Go through the other dependencies and bump any appropriate lower
  bounds
- [ ] Remove any now-unnecessary conditional compilation


## Benchmark results (for performance issues)

**Before:**

```
$ stack exec -- dejafu-tests +RTS -s

...put your results here...
```

**After:**

```
$ stack exec -- dejafu-tests +RTS -s

...put your results here...
```