Open data kinds

[Jan Stolarek]

> There is no language support to define a 
> "closed datatype" but it is possible to do so by not exporting any of
> the constructors used to make the datatype.
Data types are closed in a sense that if you define

data Foo = MkFoo1

then you cannot add new data constructor, say MkFoo2, that will also create values of type Foo. So 
being open/closed is not about creating new values of a data type but about extending the 
definition with new constructors. Does that answer your question?

Janek

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Politechnika Łódzka
Lodz University of Technology

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