Rich Neswold [EMAIL PROTECTED] writes:
For instance, I want to make a new type that is a 4 element tuple
where each element is greater than or equal to the previous entry.
data Category = Membership a a a a
You can make a 'smart' constructor function, and hide the real data
constructor so that it cannot be used:
module Category (Category(),membership) where
data Category = Membership a a a a
membership :: Ord a = a - a - a - a - Category a
membership a b c d
| d=c c=b b=a = Membership a b c d
| otherwise = error bad values
However, you probably don't really want your program to die with
error when you get badly-constrained data, so it might be better
to look into something like the Maybe type for your smart constructor:
membership :: Ord a = a - a - a - a - Maybe (Category a)
so you can catch the failing cases and do something sensible with them.
Regards,
Malcolm
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