Re: Only expose final results

[Chris Warburton]

Closing as this seems to be mostly OK now. The 'really bad' stuff is in
impure.rkt, whilst we use Nix to take care of caching.

Also note that it's been useful to expose more and more intermediate
helpers, for use in e.g. haskell-te and isaplanner-tip. We certainly
don't want to just provide e.g. a single file of generated s-expressions
and no way to access the functionality that produced it.

Rather, we want to expose intermediate steps (e.g. the original
benchmarks, the normalised benchmarks, etc.) and utility functions for
querying and manipulating these data.