deduktionstheorem at web.de
Wed Oct 1 12:32:46 EDT 2008
I've got a suggestion for the documentation of the Data.Foldable module.
The documentation  does not say anything about the order in which the
elements are folded. But as far as I understand, the order in which the
elements are traversed (i. e. the result of Data.Foldable.toList) has to
bee deterministic. The documentation of the Foldable class IMHO should
provide a clear statement about that.
Example: I implemented a heap that internally uses a tree of elements.
It uses a tree to store the elements, but two heaps might be equal
(contain the same elements) and still be represented by different trees.
instance Foldable (Heap p) where
foldMap _ Empty = mempty
foldMap f (Tree _ x l r) = foldMap f l `mappend` f x `mappend`
foldMap f r
is a bug which is not indicated by the documentation.
Thanks in advance
 using ghc-6.8.3
Früher hieß es ja: Ich denke, also bin ich.
Heute weiß man: Es geht auch so.
- Dieter Nuhr
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