Passing regexp_replace backreference to a function; type conversion problem

Question

I am trying to convert some text within my CLOB field to HTML links.
The format of the (part of the link I am having problems with) is:
<link 12>
which I wish to convert to
url_dest
I am trying to pass the backreference \1 (being the number 12 in this case) in regexp_replace to a simple function I have made and when I run it I receive the error:
ORA-06502: PL/SQL: numeric or value error: character to number conversion error
I have tested the function on its own with passing a string and it works fine.
I have passed the string from the backreference to the function and back out as the return value and it works fine.
However, when I try to pass the string back reference (a set of digits) to use as the NUMBER ID in my where clause, it always returns this error. I have tried CASTing / TO_NUMBER in every way possible I can think of, using temporary variables etc. and still the same error.
=====
CREATE OR REPLACE
FUNCTION GETLINK (linkid IN CLOB)
RETURN VARCHAR2 AS
linkstring VARCHAR2(4000);
linkchar VARCHAR(4000);
linkint NUMBER;
BEGIN
linkchar := TO_CHAR(linkid);
linkint := TO_NUMBER(linkchar);
SELECT url_dest INTO linkstring FROM TABLE WHERE ID = linkint;
RETURN linkstring;
END;
=====
Offending calling code:
tempcontent := regexp_replace(myClobField, '<link ([[:digit:]]*)>', GETLINK('\1'));
=====
I have tried implicit and explicit type conversions that vary the above function; in parameters as VARCHAR2; etc.; no joy.
Is this a bug within the database, is it by design, or is it just me making a hash of things? I really don't want to have to pull the XML into PHP then run the PHP regex functions with Oracle DB queries to do this!
Many thanks for your assistance.
Ingram

Answer 1

Many thanks for the reply, but I'm not sure how that would work. I wish to do a global regexp_replace on all instances of '<link> ([[:digit:]]*)>' within my XML document, with the return value from the GETLINK function.
So for instance.
The return value of GETLINK could be in format:
&lt;a href="\1"&gt;
so an XML document of:
=====
&lt;doc&gt;
&lt;link 12&gt;Test Link&lt;/link&gt;
some content
&lt;link 783&gt;A second Test Link&lt;/link&gt;
&lt;/doc&gt;
=====
would return as:
=====
&lt;doc>
&lt;a href="12"&gt;Test Link&lt;/link&gt;
some content
&lt;a href="783"&gt;A second Test Link&lt;/link&gt;
&lt;/doc&gt;
=====
Obviously I would then do the other replacements to fix broken XML with the non matching end tags etc.
TIA