[Haskell] Fixpoint combinator without recursion

Stefan O'Rear stefanor at cox.net
Wed Apr 4 16:41:21 EDT 2007

On Wed, Apr 04, 2007 at 01:36:18PM -0700, Michael Vanier wrote:
> For those of us who aren't type theorists: What's a "negative datatype"?

Negative isn't the usual term; we mostly call them 'contravariantly
recursive' data types, due to CT influence.  Anyways the thing to note
is that the value appears recursively, on the left of an arrow. 

data Foo = Foo (Foo -> Bool)   -- contravariantly recursive
data Foo = Foo (Bool -> Foo)   -- covariantly recursive


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