125: array:partition

[michaelhkay]

This PR revisits array:partition, with extra editorial clarification of the spec; including but not confined to fixing issue #125.

I suggest we schedule this PR for discussion since we have not previously discussed it.

One question for the group is what the name of the function should be (including the choice of namespace).

Another is whether the polarity of the callback function should be changed (from break-when to continue-when or similar).

We could also consider returning an array of sequences rather than a sequence of arrays. (But in my view sequences of arrays are rather easier to manage at the moment.)

[ChristianGruen]

One question for the group is what the name of the function should be (including the choice of namespace).

Now that you mention it, I think that fn:partition would be the best choice:

• The current name suggests that the input argument is an array.
• We shouldn’t use the array namespace just because a function returns an array,

If we want to stick with the array prefix, we could merge array:partition with array:build and introduce additional arguments (but it feels better to have fn:partition).

[michaelhkay]

I have made further changes to rename array:partition as fn:partition

[ChristianGruen]

Suggested change

	else (fn:trunk($partitions), array{$partitions[last()], $next})
	else (trunk($partitions), array{foot($partitions), $next})

[michaelhkay]

I'm not sure about all these changes.

The return type: it's an sequence of arrays; each array has one or more members, and each member is a single item. I think that's correctly expressed as array(item())*. We can't express the constraint that the array has one or members, we can only express the constraint that each member is a single item.

Use of "fn:" prefix. In the past examples in the specs have always had a convention that calls to functions in the fn namespace are prefixed. It's a bore and I'd like to get rid of it (and it's sometimes honoured in the breach) but I think it should be done systematically if it's going to be done at all.

[ChristianGruen]

I think that's correctly expressed as array(item())*.

So true. Sorry. About time to skip the morning hours again.

Use of "fn:" prefix. In the past examples in the specs have always had a convention that calls to functions in the fn namespace are prefixed.

Interesting: I spotted many examples that omitted the prefix (that’s even the case in the given pull request – see last(), count(), boolean(), sum(), etc.), so I assumed the convention is that the prefix shall exclusively be used for the function that’s presented. Good to know. And I agree, it’s probably better to sanitize this separately.

I think there’s just one example that would be better readable – if written as trunk($partitions), array{foot($partitions).

[ChristianGruen]

@michaelhkay I’m afraid, it seems the PR needs to be fixed due to my cleanups.

[michaelhkay]

I'm going to scrap this PR and raise a new one.