don't have sepBy0 and sepBy1 do complicated processing to their values

[mattfenwick]

Just return something like:

{'first': ..., 'pairs': [[..., ...], ...]}

Perhaps wrapped in a datatype that knows how to return all the values while ignoring the separators.

[mattfenwick]

This will simplify the operators combinators, as they won't have to deal with that funky datatype anymore.

[mattfenwick]

Done.

[mattfenwick]

This could maybe be taken even further, and have sepByN build the tree, as well.
They'd have to decide whether to left- or right-associate it, though.