[Haskell-cafe] Re: defining last using foldr

On 2007-08-14, Chaddaï Fouché wrote:

2007/8/14, Alexteslin :

...

Well, i have tried cons (:) operator but when it passed to foldr doesn't work because cons operator operates first character and then the list but the foldr argument takes a function (a->a->a). Maybe i am missing the point here?

What Aaron was saying was that in this list : 1 : 2 : 3 : 4 : [] A fold replaced the cons (:) by another function (and [] by another constant).

Your problem isn't so easy to do with a foldr, a foldl would be easier and a foldr1 or foldl1 even better. Are you sure you can't use one of those other folds ?

The problem with foldl is that you can't easily make it polymorphic because of how the null case is handled. foldl1 and foldr1 are trivial, true. -- Aaron Denney -><-