On Sat, Apr 1, 2017 at 6:47 AM, Alex Shinn <xxxxxx@gmail.com> wrote:

SRFI 128 mentions nothing about cyclic data structures.

See the paragraph "Limitations" in the specification section:

The comparator objects defined in this SRFI are not applicable to circular structure or to NaNs, or to objects containing any of these. Attempts to pass any such objects to any procedure defined here, or to any procedure that is part of a comparator defined here, is an error except as otherwise noted.

 

In particular, the eq-comparator and the eql-comparator handle circular structure and NaNs, and the equal-comparator does iff `equal?` does.