701: fn:concat: Support for 0 or more arguments

[ChristianGruen]

Closes #701

[michaelhkay]

For a bit more precision, I'd suggest defining it as:

This function accepts zero or more arguments, each declared with the required type xs:anyAtomicType*. The value supplied for each argument is reduced to a single string by applying the fn:string-join#1 function; the resulting sequence of strings (one for each supplied argument) is then reduced to a single string by a further application of fn:string-join#1.

[michaelhkay]

Hmmm... I think that accepting sequences breaks 1.0 compatibility mode. In XPath 1.0, concat(//h1, //h2) concatenates the value of the first h1 element and the first h2 element. XPath 4.0 in 1.0 compatible mode would no longer reproduce that behaviour. Perhaps we should drop that part of the proposal.

We could make the actual semantics of the function dependent on whether compatibility mode is set in the static context. I don't think we have a precedent for that, but I can't see any harm in it.

[ChristianGruen]

the resulting sequence of strings (one for each supplied argument) is then reduced to a single string by a further application of fn:string-join#1.

I wonder if it would make a difference to invoke string-join just once for all strings, or repeatedly for the strings of each argument?

We could make the actual semantics of the function dependent on whether compatibility mode is set in the static context.

Would be fine by me. I might be overwhelmed finding the right wording, though. Would you be ready to revise the PR?

[michaelhkay]

I wonder if it would make a difference to invoke string-join just once for all strings

It wouldn't make a difference, it would just be a little bit more difficult to define (I think).

[michaelhkay]

For 1.0 compatibility, try:

This function accepts zero or more arguments, each declared with the required type xs:anyAtomicType*. The value $A supplied for each argument is first reduced to a single string as follows:

• if XPath 1.0 compatibility mode is set to true in the static context of the function call, then the result of xs:string($A[1])

• Otherwise, the result of fn:stirng-join($A)

The resulting sequence of strings (one for each supplied argument) is then reduced to a single string by applying the function fn:string-join#1 to the sequence.

[ChristianGruen]

Revised as suggested, thanks.

[ndw]

The CG agreed to accept this PR at meeting 046.