[DFDL-WG] proposal: add fn:trace function to DFDL

[Mike Beckerle]

I have found working with DFDL expressions basically impossible without the
fn:trace function to help debug them.

I am not sure how I would write a tutorial about expressions without using
fn:trace in it to illustrate what is going on in the expressions. In the
interests of keeping the tutorials portable I suggest we add the fn:trace
function.

fn:trace($value as item()*, $label as xs:string) as item()*

Summary: Provides an execution trace intended to be used in debugging
queries.

The notation item()* means any node sequence including an empty node
sequence.

The input $value is returned, unchanged, as the result of the function. In
addition, the inputs $value, converted to an xs:string, and $label may be
directed to a trace data set. The destination, format, and ordering of the
output of this trace data set is implementation specific.

Related Issue: I don't see any language in the spec where we flat out say
that a node sequence in the expression language is a sequence of Infoset
Element Information Items. We should add this near the begining of section
23.


-- 
Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology |
www.tresys.com
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