Think about it like this:
[image: image.png]
The current elements are zipped with the tails (which are created with
transpose). This has to bottom out with empty tails (repeat []).
On Sat, Apr 24, 2021 at 2:32 AM Galaxy Being
I'm in Bird's *Thinking Functionally with Haskell *and he has this code to transpose a matrix based on a list of row lists
transpose :: [[a]] -> [[a]] transpose [xs] = [[x] | x <- xs] transpose (xs:xss) = zipWith (:) xs (transpose xss)
then he says transpose can be rewritten with this pattern
transpose [] = ...
what could be the rest of it? The answer he gives is
transpose2 :: [[a]] -> [[a]] transpose2 [] = repeat [] transpose2 (xs:xss) = zipWith (:) xs (transpose2 xss)
where repeat [] gives an infinite list of repetitions. And, he says, note that
transpose [xs] = zipWith (;) xs (repeat []) = [[x] | x <- xs]
I suppose I get this last equation, but I don't understand repeat in transpose2. Can someone explain this to me?
LB
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