[Haskell-cafe] A Foldable binary search tree
ndmitchell at gmail.com
Sun Dec 23 06:42:52 EST 2007
> > 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:
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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