[Haskell-cafe] Re: Constructor constraints

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"Rich" == Rich Neswold writes: Hello, I've looked through the two tutorials and the Report, but couldn't find help on this topic. My question is whether you can place constraints on new data types. 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. Is this possible?

i.e.

data Category = Membership a a a a

I'd like to be able to prevent invalid Category data from being created. Any information would be appreciated.

Don't export constructors and define functions which will imply your constraints. module Foo (..., Category,... makeCategory1, makeCategory2, ...) -- WBR, Max Vasin.