How would you define map and filter using foldr in Haskell?

Question

I\'m doing a bit of self study on functional languages (currently using Haskell). I came across a Haskell based assignment which requires defining map and filter in terms of

Answer 1

I wish I could just comment, but alas, I don't have enough karma.

The other answers are all good ones, but I think the biggest confusion seems to be stemming from your use of x and xs.

If you rewrote it as

map'            :: (a -> b) -> [a] -> [b]
map' f []       = []
map' f (x:xs)   = foldr (\y ys -> (f y):ys) [] xs

you would clearly see that x is not even mentioned on the right-hand side, so there's no way that it could be in the solution.

Cheers