I'm totally confused but I can't find any solution to my problem... When I
remove List.head from the currentBox function, I can see that it returns a
list of Nothing. So I thought I could add a List.filter function in order
to return only the box I wanted, like this :
currentBox boxId =
cells
|> List.map (filterRow boxId)
|> List.filter (\box -> box.id == boxId)
But the compilet complains that :
(|>) is expecting the right argument to be a:
List (Maybe Box) -> a
But the right argument is:
List { a | id : Int } -> List { a | id : Int }
I'm sorry but I don't understand. Since cells |> List.map (filterRow
boxId) returns a list, why can't I do a filter on this list? I'm not so
familiar with Maybe, so maybe the problem is there...
Le mercredi 26 octobre 2016 14:05:34 UTC+2, Wouter In t Velt a écrit :
>
> Op woensdag 26 oktober 2016 13:36:18 UTC+2 schreef Did:
>>
>> But It seems that, in the update function, currentBox always return
>> something because it doesn't update my model... I'm obviously doing
>> something wrong. But, for me, as all cells are unoccupied, this test should
>> return Nothing. What's wrong ?
>>
>
> The output of the currentBox function is not Nothing, but it is Just
> Nothing. A bit of a strange outcome.
> If you remove the |> List.head from the currentBox function, you can see
> where things go wrong.
>
> I'm sorry, but I don't know how to debug elm code in general, and in
>> particular with the elm lang try editor (I'm at work and I don't have elm
>> working on my machine...)
>>
>
> Below is a quick test I did in elm lang try editor. You can copy/paste
> this.
> With elm, it is relatively easy to test parts of your code (because all
> functions are "pure", so the same input always gives the same output.)
>
> import Html exposing (text)
>
> type alias Box = { id : Int, player : Maybe Int }
>
> filterRow: Int -> List Box -> Maybe Box
> filterRow boxId row =
> row
> |> List.filter (\box -> box.id == boxId && not (box.player == Nothing))
> |> List.head
>
> currentBox boxId =
> List.map (filterRow boxId) cells
> |> List.head
>
> cells =
> [ [ Box 1 Nothing, Box 2 Nothing, Box 3 Nothing ]
> , [ Box 4 Nothing, Box 5 Nothing, Box 6 Nothing ]
> , [ Box 9 Nothing, Box 8 Nothing, Box 9 Nothing ]
> ]
>
> main =
> text <| toString <| currentBox 5
>
>
>
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