[Haskell-cafe] A Foldable binary search tree

Neil Mitchell ndmitchell at gmail.com
Sun Dec 23 06:42:52 EST 2007

Hi Brad,

> > Experience has taught me to _never_ put class contexts on data
> > definitions. Now you can't write something as simple as "Empty" - you
> > have to give it a class context. This is just plain annoying.
> With the class context in the BST definition, ghc gives no complaints when
> I evaluate "Empty":

In some circumstances, you need to give a type sig. For example using Hugs:

Main> Empty
ERROR - Cannot find "show" function for:
*** Expression : Empty
*** Of type    : BST a

I guess GHC has enough defaulting to display this anyway.

You'll also have the dreaded-evil-horrid monomorhpism restriction if you type.

empty = Empty



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