id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	difficulty
474	Additional library procedure condition->list	Christian Kellermann	felix winkelmann	"I would like to add introspection facilities for conditions to our chicken library core. Programs should be able to know which properties are available.

Rationale:

Programs currently have not a good method of inspecting conditions. Property names have to be known in advance, there is no introspection facility as there is no way of querying the properties that are available.

csi's describe function atm does peek inside the slots directly.

Sometimes I do have the need to convert exceptions programmatically to either some other exception or structure. The way this can be done up to now is to use ##sys#slot and peek into the internal record structure which is fragile.

After some initial thoughts there is:

Way 1: 

With the exception->list procedure properties and their values are returned in one list, ordered by exceptions.

Example:

{{{
    Example:
    (condition->list http-client-condition)
     => ((exn (arguments
                (#<URI-common:...>))
              (message ""Client error: 400 Bad Request"")
              (location call-with-input-request))
         (http)
         (client-error
            (body ""\""invalid UTF-8 JSON\""}"")
            (response #<response>)))
}}}

(output shortened for readability)

Way 2:
Why everything into one list? Well I guess it could be split up into two parts, a query api for introspection and then the usual get-condition-property-accessor dance as well. For composite conditions this could amount to lists like:

{{{
((exn location arguments message)
 (http)
 (client-error response body))
}}}

This could then again traversed to extract the wanted properties.

I have attached a patch that implements this procedure as described in way 1. As well the additional test case for it. As a bonus it adds test cases for the exception slots so we can tell it this breaks in the future.

I am interested in suggestions or even a better way to do this. Maybe way 3..."	enhancement	closed	major	4.9.0	core libraries	4.6.x	fixed	condition->list