One interesting pattern

Question

I'm solving 99 Haskell Probems. I've successfully solved problem No. 21, and when I opened solution page, the following solution was proposed:

Insert an element at a given position into a list.

insertAt :: a -> [a] -> Int -> [a]
insertAt x xs (n+1) = let (ys,zs) = split xs n in ys++x:zs

I found pattern (n + 1) interesting, because it seems to be an elegant way to convert 1-based argument of insertAt into 0-based argument of split (it's function from previous exercises, essentially the same as splitAt). The problem is that GHC did not find this pattern that elegant, in fact it says:

Parse error in pattern: n + 1

I don't think that the guy who wrote the answer was dumb and I would like to know if this kind of patterns is legal in Haskell, and if it is, how to fix the solution.

Answer 1

I believe it has been removed from the language, and so was likely around when the author of 99 Haskell Problems wrote that solution, but it is no longer in Haskell.