[FO] Built-in function changes to support default values

[rhdunn]

This issue tracks the changes needed to the built-in functions to allow them to combine the declarations into a single definition with default parameter values.

The general approach to this is to make required arguments optional if they are for a function signature that is not the lowest argument count signature, and move any associated logic into the function.

array:subarray

1. Change array:subarray/$length from xs:integer to xs:integer?.

Rules

Except in error cases, the result of the function is the value of the expression op:A2S($array) => fn:subsequence($start, $length) => op:S2A().

Error Conditions

A dynamic error is raised [err:FOAY0001] if $start is less than one or greater than array:size($array) + 1.

A dynamic error is raised [err:FOAY0002] if $length is not an empty sequence and is less than zero.

A dynamic error is raised [err:FOAY0001] if $length is not an empty sequence and $start + $length is greater than array:size($array) + 1.

fn:concat

This should be modified to use a sequence-variadic signature, either as a 1 parameter function (taking an xs:anyAtomicType* value, allowing 0 and 1 arguments), or a 3 parameter function with the last parameter having the type xs:anyAtomicType*.

fn:differences

The $options parameter should be moved to the end of the parameter list in order to make the function a map-variadic function when default values are applied. This then makes it possible to specify the collation argument using a keyword argument in addition to specifying options as keyword arguments.

fn:resolve-uri

1. Change fn:resolve-uri/$base from node() to node()?.

- If the $base argument is not supplied,
+ If the $base argument is the empty sequence,

fn:subsequence

1. Change fn:subsequence/$length from xs:double to xs:double?.

When $length is the empty sequence, this function returns:

$input[fn:round($start) le position()]

When $length is not the empty sequence, this function returns:

$input[fn:round($start) le position() 
         and position() lt fn:round($start) + fn:round($length)]

fn:substring

1. Change fn:subsequence/$length from xs:double to xs:double?.

More specifically, when $length is not the empty sequence the function returns the characters in $value whose position $p satisfies:

fn:round($start) <= $p and $p < fn:round($start) + fn:round($length)

When $length is the empty sequence the function assumes that $length is infinite and thus returns the ·characters· in $value whose position $p satisfies:

fn:round($start) <= $p

fn:tokenize

1. Change fn:tokenize/$pattern from xs:string to xs:string?.

If $pattern is the empty sequence, the $value argument is set to fn:normalize-space($value) and $pattern is set to ' '.

fn:unparsed-text / fn:unparsed-text-available

1. Change fn:unparsed-text/$encoding from xs:string to xs:string?.
2. Change fn:unparsed-text-available/$encoding from xs:string to xs:string?.

fn:unparsed-text-lines

1. Change fn:unparsed-text-lines/$encoding from xs:string to xs:string?.

The result of the function is the same as the result of the expression fn:tokenize(fn:unparsed-text($href, $encoding), '\r\n|\r|\n')[not(position()=last() and .='')].

Collations

1. Change fn:collation-key/$collation from xs:string to xs:string?.
2. Change fn:compare/$collation from xs:string to xs:string?.
3. Change fn:contains/$collation from xs:string to xs:string?.
4. Change fn:contains-token/$collation from xs:string to xs:string?.
5. Change fn:deep-equal/$collation from xs:string to xs:string?.
6. Change fn:differences/$collation from xs:string to xs:string?.
7. Change fn:distinct-values/$collation from xs:string to xs:string?.
8. Change fn:ends-with/$collation from xs:string to xs:string?.
9. Change fn:index-of/$collation from xs:string to xs:string?.
10. Change fn:max/$collation from xs:string to xs:string?.
11. Change fn:min/$collation from xs:string to xs:string?.
12. Change fn:starts-with/$collation from xs:string to xs:string?.
13. Change fn:substring-after/$collation from xs:string to xs:string?.
14. Change fn:substring-before/$collation from xs:string to xs:string?.
15. Change fn:uniform/$collation from xs:string to xs:string?.
16. Change fn:unique/$collation from xs:string to xs:string?.

Passing the empty sequence to the $collation argument is equivalent to supplying the default collation to that argument.

[michaelhkay]

I'm writing a detailed PR along these lines, but I'm handling collations differently; rather than allowing the supplied value to be an empty sequence, I'm defining the default as $collation := fn:default-collation().

But I agree that where the default is complex, as with the $encoding parameter of fn:unparsed-text(), the best solution is probably to allow () as a value, and make it the default.