[mercury-users] Extending a structure data type in Mercury

[Ralph Becket]

Gregory D. Weber, Saturday,  4 June 2005:
> I want to "extend" a structure type by adding fields, like this:
> 
> :- type prule ---> prule(key, class, ftable, conds).
> :- type cn2rule == prule.
> :- type icnrule ---> icnrule(key, class, ftable, conds, info).
> 
> But want icnrule to be considered a subtype of prule,
> also as a subtype of cn2rule, so that procedures developed for prules 
> and cn2rules will also work for icnrules.
> 
> I've found a solution, but I'm wondering if there's a better way.

Hmm.  I think you might find it easiest to do this sort of thing using
type classes.  Would that work?

-- Ralph
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