[Haskell-beginners] abstype?

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? -- frigidcode.com theologia.indicium.us