Hi Patrik:

there seem to be different ranges of polytypicity.

There are the strongly polytypic algorithms that you advocate
that you write once for a data type format and then we get an algorithm
for all data types satisfying that format.

There are the weakly polytypic algorithms 
that you write once for a data type T and then we get an algorithm
for all data types similar to T.

Are you also doing "weakly polytypic algorithms" for some definition
of similarity?

-- Karl