Re: [Haskell-cafe] Newbie Question on type constructors

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Put the data declaration in a module, export the type, but not the constructor you want to hide:

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module Shape (Shape(Square), circle) where

Since we were talking about 'what can one do with a constructor as compared with a function', it should be mentioned that this also has a disadvantage: you loose pattern matching outside the module. I.e. no longer can say [..] BTW, would it be possible (in principle) to allow constructor export 'read-only', so matching against a constructor is allowed but not constructing a value?

OCaml has this: http://caml.inria.fr/ocaml/htmlman/manual021.html#htoc99 --KW 8-) -- Keith Wansbrough <kw217@cl.cam.ac.uk> http://www.cl.cam.ac.uk/users/kw217/ University of Cambridge Computer Laboratory.