> It seems to me that it might be very useful for a module to export the
> pattern matching operators for a datatype without exporting the
> constructors. Suppose we have
>
> data A = X {a::Int, b::Float}
>
> And we want to maintain the invariant that b is a floating-point
> representation of a. So normally we would have to use a completely
> abstract datatype, and provide constructors and destructors. But in
> this case, it would actually make sense to provide the
> pattern-matching
> operator X, but not the data constructor X. So I think it
> would be good
> to separate these in the module export syntax.
What's wrong with
module M (A, a, b) where { ... }
?
Simon
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