I have just committed the code for the alternative formulation of SYB3. It requires neither higher-rank types nor mutually recursive instances. Therefore, the code works even in Hugs (the original SYB3 code does not work in Hugs). The files are in the directory SYB31/. The `final' code is dat2.hs (dat1.hs is the `intermediate' step, which makes it easy to understand `dat2.hs'). The code has comments that describe which part of the code is the `Library', which part of the code is the `generic function' (independent of the data structure), and which part of the code overrides some general processing of the generic function. The code has two examples; one of them is gsize, from the original SYB3 paper. I'd like to suggest two corrections to the SyB page: first, rank-2 types are not necessarily required for all flavors of SYB second, the original SYB3 imposes one more requirement: mutually recursive instances. It is rarely mentioned -- but not universally implemented (Hugs does not have it). SYB31 shows that one can get by without that requirement. At the ICFP05 talk, Simon Peyton-Jones asserted that recursive instances are essential. I have publicly expressed doubts. Simon Peyton-Jones said: if you think otherwise, show me the code. And so I did.