[Haskell-cafe] Re: Deleting list of elements from Data.Set

apfelmus apfelmus at quantentunnel.de
Wed Jan 30 09:50:26 EST 2008

Gracjan Polak wrote:
>> Data.List.foldr (Data.Set.delete) s [1,3,5]
>> or
>> Data.List.foldl' (flip Data.Set.delete) s [1,3,5]
> There will be a day when I finally grasp foldr/foldl :)



helps to make that day dawn earlier :)

Note that in your original approach of  fold (.) id  , it doesn't really 
matter whether you use  foldr  or  foldl'  (except for argument order!) 
because the latter would only evaluate to a function  Data.Set -> 
Data.Set  which is not very useful. In contrast, Duncan's code evaluates 
to  Data.Set  , that's what you want to be strict in.


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