Packages are now installed in a directory with their version number.
On adding a package directory, we now look in a local 'depends'
directory first (to allow packages to be installed locally to another
project) before the global install directory.
Dependencies can have version bounds (details yet to be implemented) and
we pick the package with the highest version number that matches.
This is an alternative to using `fastUnpack` and `fastPack` to work
on lists of characters.
Using this to refactor the lexer and benchmarking the resulting
compiler on building idris2 shows it's 3 to 5s slower than the
current implementation that goes via `List Char`.
This may be backend-dependent so I still push this to contrib,
with the plan of running further benchmarks in the future.
Ideally, liftIO would always be linear, but that has lots of knock-on
effects for other monads which we might want to put in HasIO, now that
subtyping is gone. We'll have to revisit this when we have some kind of
multiplicity polymorphism.
It's disappointing to have to do this, but I think necessary because
various issue reports have shown it to be unsound (at least as far as
inference goes) and, at the very least, confusing. This patch brings us
back to the basic rules of QTT.
On the one hand, this makes the 1 multiplicity less useful, because it
means we can't flag arguments as being used exactly once which would be
useful for optimisation purposes as well as precision in the type. On
the other hand, it removes some complexity (and a hack) from
unification, and has the advantage of being correct! Also, I still
consider the 1 multiplicity an experiment.
We can still do interesting things like protocol state tracking, which
is my primary motivation at least.
Ideally, if the 1 multiplicity is going to be more generall useful,
we'll need some kind of way of doing multiplicity polymorphism in the
future. I don't think subtyping is the way (I've pretty much always come
to regret adding some form of subtyping).
Fixes#73 (and maybe some others).
