[ssax-sxml] Re: custom sxpath convertors yielding non-sxml objects

[<ol...@po...>]

Hello!

>  1. Is it possible and proper for a custom SXPath convertor to yield
>     output as *non*-SXML Scheme objects, when in the last step of an
>     SXPath query?

A converter is defined as a Node|Nodelist -> Nodelist. It's highly
desirable to abide by that signature. However, this requirement is not
much an imposition: you can still do what you want. A custom converter
should accept a nodelist, and return a proper list. If this list is
non-empty, each element must be either
	- a proper list whose car is a symbol, or
	- *anything* else

The SXML specification says that a Node, if it is not a proper node,
must be a text string. It is certainly true for SXML produced by
ssax:xml->sxml, but it is not strictly necessary. It's quite
convenient, for example, to write integers in their "native" format
rather than as strings of digits. It is sometimes convenient to use
procedural values.

Therefore, your example can be written as something like the following:

((sxpath `(// a @ href *text* ,custom)) sxml)

where
(define (custom attr-val)
 (let ((posn (regexp-match regexp attr-val)))
   (if posn (extract-match posn attr-val) '())))

Actually, I checked that at least in the old SXPath code, the custom
converter is not even obliged to return a nodelist. A node
suffices. So the function extract-match above can return basically
anything it wishes to. If it returns a list, the list would be spliced
in. Care should be taken in only one case: when returning an improper
list or a list that should not be spliced in. Such a value can always
be wrapped into a 1-arg vector or a closure.