Write a tail recursive version of the map function

Question

Willie · Accepted Answer

let map f l =
    let rec map' f l x =
        match l with
            |[] -> x []
            |hd::tl -> map' f tl (fun lst -> x ((f hd)::lst))
    in
    map' f l (fun lst -> lst)
;;

Matthieu · Answer

The previous answer seems a bit too complex, i would rewrite it as :

let rec mytailmap f m =
   let rec aux f m result =
      match m with
         | [] -> result
         | h::t -> aux f t (result@[(f h)])
  in aux f m [] ;;

val mytailmap : ('a -> 'b) -> 'a list -> 'b list =

Utilisateur anonyme · Answer

```
tailMap :: (a->b) -> ([b]->[b]) -> [a] -> [b]
tailMap _ _ [] = []
tailMap f k (x:[]) = k [f x]
tailMap f k (x:xs) = tailMap f (\r -> k $ ((f x) : r)) xs
```

Jane Street

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