`fn:append`

[ChristianGruen]

It is trivial to append items to a sequence, but it is a bit counterintuitive to do so the functional way, for example within chains:

(1, 3, 5)
=> fn { ., 7, 9 }()
=> string-join(',')

I propose adding a simple fn:append function, as counterpart of array:append:

(1, 3, 5)
=> append((7, 9))
=> string-join(',')

It is easier to prepend items: we already have fn:insert-before (and array:insert-before).

[michaelhkay]

No objections, though I'm not convinced it's a must-have.

[ruv]

(1, 3, 5)
=> fn { ., 7, 9 }()

Why not:

(1, 3, 5)
-> ( . , 7, 9 )

It is easier to prepend items: we already have fn:insert-before (and array:insert-before).

But prepending is not much easier than appending using fn:insert-before in both cases:

Appending:

(1, 3, 5)
=> insert-before( xs:float("INF"), (7,9) )

Prepending:

(1, 3, 5)
=> insert-before( 1 , (7,9) )

Thus,

let $prepend := insert-before( ?, 1, ?)
let $append := insert-before( ?, xs:float("INF"), ?)

[ChristianGruen]

(1, 3, 5)
=> fn { ., 7, 9 }()

Why not:

(1, 3, 5)
-> ( . , 7, 9 )

True; this variant will definitely become an option in chains, thanks to your proposal that changes the grammar rules.

The proposed function is mostly supposed to be a convenience solution for those who are not aware of the full range of features. In addition, we tried to offer equivalent functions for arrays that exist for sequences, and vice versa, and this one is clearly missing (there is no equivalent solution for array:put either; but fn:put has been taken by XQuery Update).

[michaelhkay]

The new function is presumably semantically equivalent to the function op(","). We're again in danger of providing more than one solution to the same problem.

The difficulty with the reasoning

The proposed function is mostly supposed to be a convenience solution for those who are not aware of the full range of features.

is that the more features we add, the more we increase this problem.