Tomasz Zielonka wrote:
It's quite easy if you allow the indices to be put in a single compound value.
Hmm. Well, I guess I don't need to insist on the exact type that I gave in the statement of the puzzle - although something like that would be the nicest. This is actually a function that is useful quite often in practice. But I would rather not be forced to write things like
replace (I 0 $ I 2 $ I 3 $ ())
in my code. My first attempt was very similar to yours, except I used
replace (0, (2, (3, ())))
instead of your Index type. I don't like my solution, either. So I guess I would define a full solution as something nice enough to be used in practice. Let's be more concrete - it has to be nice enough that most people who need, say, replace2 or replace3, in real life, would actually use your function instead of writing it out by hand. Maybe others would disagree, but so far, I personally do not use either your solution or my solution. I write it out by hand.
If you insist that each index should be given as a separate function argument, it may be possible to achieve it using the tricks that allow to write the variadic composition operator.
I am not familiar with that. Do you have a reference? Is that the best way to do it? (Is that a way to do it at all?) Thanks, Yitz _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
