[Hat] Cycles

[Malcolm Wallace]

Thomas Davie <tom.davie at gmail.com> writes:

>    I was just wondering if anyone had a 'definitive' list of where it is 
> possible to get a cycle in an ART.  Has anyone looked at where it is 
> theoretically possible to get a cycle and what code causes it?  Or, if 
> not, does anyone have a list simply from the experience of writing the 
> SExp cycle detection code.  I'm having a few problems deciphering 
> exactly what it is looking for.

Thorsten Brehm, the author of the cycle-detection code, would be
the best person to ask.  Unfortunately, his Master's Thesis about
the implementation of the Hat tools does not mention the subject of
cycles at all.

One obvious source of a cycle in the trace would be genuinely
circular code:

    let xs = 1:xs in xs

Beyond situations like this, I'm not sure.
Regards,
    Malcolm