Maybe interesting to know: in the svn the error is gone:
haftmann@macbroy15:/home/nfs_data$ /opt/polyml/polyml-svn/x86-linux/poly Poly/ML 5.4.1 Testing datatype 'a T = T of ('a * 'a T) list; datatype 'a S = S of 'a T;
datatype 'a T = T of ('a * 'a T) list datatype 'a S = S of 'a T
Sorry for not having tested this before the first posting.
Florian