I tend to prefer moving toward explicit exception handling, not away from
it, but in this case, I think there are good reasons to let checkPresent
throw exceptions:
1. They can all be caught in one place (Remote.hasKey), and we know
every possible exception is caught there now, which we didn't before.
2. It simplified the code of the Remotes. I think it makes sense for
Remotes to be able to be implemented without needing to worry about
catching exceptions inside them. (Mostly.)
3. Types.StoreRetrieve.Preparer can only work on things that return a
Bool, which all the other relevant remote methods already did.
I do not see a good way to generalize that type; my previous attempts
failed miserably.
Pass subcommand as a regular param, which allows passing git parameters
like -c before it. This was already done in the pipeing set of functions,
but not the command running set.
Many functions took the repo as their first parameter. Changing it
consistently to be the last parameter allows doing some useful things with
currying, that reduce boilerplate.
In particular, g <- gitRepo is almost never needed now, instead
use inRepo to run an IO action in the repo, and fromRepo to get
a value from the repo.
This also provides more opportunities to use monadic and applicative
combinators.
Avoid ever using read to parse a non-haskell formatted input string.
show :: Key is arguably still show abuse, but displaying Keys as filenames
is just too useful to give up.
