Add more ergonomic ways to define folds and scans

[harendra-kumar]

Flipped versions of folds are better when we need to define the fold inline.

primes :: MonadIO m => Fold m Int (MutArray Int)
primes =
      flip Fold.foldlM' (pure MutArray.empty)
    $ \arr n -> do
        isPrime <-
            Stream.fold (Fold.all (\p -> n `mod` p /= 0))
                $ Stream.takeWhile (\p -> p * p <= n)
                $ MutArray.read arr
        if isPrime
        then MutArray.snoc arr n
        else pure arr

We can call the flipped version as foldWith. We can also add a termination condition, which makes it more like a familiar for loop.

The applies to scans as well.