Since this special one_instance function uses global state, if it's
re-used in more than one test, this won't work since they still all use
the whole global state. Make new ones for each test.
This also breaks the count=2 feature (any number other than 1) when
running these, which is not ideal. Create a cleanup API that we can run
between tests to reset the global state.
This adds ExprTopLevel and ExprSingleton and ensures that ExprBind is
now monomorphic.
This corrects a previous design bug where it was not monomorphic and
would thus cause spawning of many more copies than necessary. In most
cases this was only harmful to memory and performance, and not
behaviour, since these functions were pure, and we didn't have a test
for this.
This also adds a bunch more tests. Most notably, the graph shape tests
generally produce smaller graphs now.
Lastly, a lambda cannot have two different types when used at two
different call sites. It is rare that this would be used, and when it
would make sense, there are easy workarounds to accomplish equivalent
goals.
This was mostly authored by Sam, James helped with some cleanup and
debugging.
Co-authored-by: James Shubin <james@shubin.ca>
