[Haskell-beginners] abstype?

[Christopher Howard]

In my older (1992) intro programming book, the author uses the keyword 
"abstype" instead of "data" inside of module code. From what I can 
gather, abstype is supposed to hide constructors. But I've never seen 
this keyword used in any modern tutorials I've gone through. Is 
"abstype" still a valid keyword? Is is still relevant?

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