Add Map.fromListUnique

[Dean177]

val fromListUnique :
     ('key, 'identity) Comparator.s
  -> ('key * 'value) list
  -> (('key, 'value, 'identity) t, 'key) Result.t

This function should work similarly to fromList but will return an Ok if all of the keys are distinct and an Error containing the duplicated key if it is encountered.

Naming suggestions would be helpful.

[shubhamkumar13]

The keys that would be of Error type would they be still part of the sorted list? Where now it would be sorted in terms of value?

for eg. if the input is [(2, "b"), (1, "a"), (2,"c"), (3, "d")] the output should be [ Ok (1, "a"), Ok (2, "b"), Err (2), Ok (3, "d")] ?

also if there are multiple occurrences what output should it take?

[shubhamkumar13]

So I wrote a function

  let f arr = Array.fold_left (fun acc x -> 
    ((Array.fold_left (fun acc i -> 
      match (Stdlib.compare (fst i) (fst x)) with 
      | 0 -> acc + 1 
      | _ -> acc) 0 arr), acc, x) |> fun (sum,acc,x) -> 
        if sum = 1 then 
          (Result.ok x) :: acc 
        else 
          (Result.error (fst x)) :: acc) [] arr |> Array.of_list

Which takes an input for eg. -> [| (2, "b"); (1, "a"); (2,"c"); (3, "d") |]
And this outputs -> [| Ok (3, "d"); Error 2; Ok (1, "a"); Error 2 |]

But I don't know how to use fromArray or create a custom comparator

[pbiggar]

Thanks for doing all this work!

I think there's a slight misunderstanding as to the intent of this. As you process the list, you should be adding the keys/values to a Map, not making another list.

The Ok is intended to be a ('key, 'value, 'comparator) Map.t with the key/values from the list in it. The Error case just has the key.

So:

Map.fromListUnique [ (2, "b"); (1, "a"); (2,"c"); (3, "d") ] = Error 2

Does that clear things up?