在更新中有条件地更改记录

Question

我希望在Msg上使用一些逻辑，并根据结果以不同的方式对视图进行update处理。

我正在翻转一些卡片，我想测试其中两张。然后，将它们作为一对接受，或者丢弃并重试。

update : Msg -> Model -> Model
update msg model =
case msg of
ClickedCard data ->
{ model
| activeCard = data.id
, (if List.lenght selectedCards < 2 then
selectedCards = data.id :: model.selectedCards
else if (List.take 1 model.selectedCards) == (List.drop 1 model.selectedCards) then
completedPairs = ( List.take 1 model.selectedCards , List.drop 1 model.selectedCards ):: model.completedPairs
else
selectedCards = List.drop 2 model.selectedCards)
}
_ ->
model

但是，我似乎无法在那里插入逻辑。我应该把它放在哪里？

-- PROBLEM IN RECORD ------------------------------------------ src/Flipping.elm
I am partway through parsing a record, but I got stuck here:
126|             { model
127|                 | activeCard = data.id
128|                 , (if List.lenght selectedCards < 2 then
^
I was expecting to see another record field defined next, so I am looking for a
name like userName or plantHeight.

Answer 1

记录更新语法不是这样工作的。

您可以执行以下操作。

update : Msg -> Model -> Model
update msg model =
case msg of
ClickedCard data ->
let 
newModel = { model | activeCard = data.id }
in
if List.length selectedCards < 2 then
{newModel | selectedCards = data.id :: model.selectedCards}
else if (List.take 1 model.selectedCards) == (List.drop 1 model.selectedCards) then
{newModel | completedPairs = ( List.take 1 model.selectedCards , List.drop 1 model.selectedCards ):: model.completedPairs}
else
{newModel | selectedCards = List.drop 2 model.selectedCards)}
_ ->
model