[syrak]

Thanks! Here we go: "Note: In versions of Miranda before release two (1989) it was possible to associate "laws" with the constructors of an algebraic type, which are applied whenever an object of the type is built. For details see Turner 1985, Thompson 1986. This feature was little used and has since been removed from the language. "

[082349872349872]

fwiw I unwittingly retrod this path; looking back at early versions of my algebraic type library there were all sorts of provisions for automatic smart constructors (commutativity, identities, etc., surely inspired by Goguen) that got dropped from later versions for lack of use.

[derriz]

Cool - mystery solved!