abstype is not currently a keyword in Haskell. To hide constructors from client modules, use an explicit module export list, and don't include the constructors in the list. For example, module MyModule ( Foo ) where data Foo = Bar Int | Baz Float | Bat Double will make Foo an abstract type, since Bar, Baz, and Bat are not exported. Similarly, module MyModule ( Foo ) where data Foo = Foo Int will also make Foo an abstract type, since Foo in the export list refers to the type Foo, not the constructor Foo (which happens to have the same name). To export Foo and its constructors, use Foo (..) in the export list, or list the constructors explicitly: Foo ( Bar, Baz, Bat ) for the first example, or Foo ( Foo ) for the second example. Hope that helps. Alexander On 14 August 2011 22:06, Christopher Howard wrote:

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

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