sorry, I meant
init = update (FetchStatus 0) initialModel
Den onsdag 8 mars 2017 kl. 22:53:43 UTC+1 skrev Martin Norbäck Olivers:
>
> You don't need to send a command. Just "kick off" your initial model by
> doing
> init = ( update (FecthStatus 0) initialModel, Cmd.none)
>
> Den onsdag 8 mars 2017 kl. 22:50:00 UTC+1 skrev Duane Johnson:
>>
>> Preface: while I've been using Elm for a while, I've only just begun
>> using messages and commands, so it's ok to treat me like a newbie here.
>> This is a capture of my experience of Elm while trying to figure out how to
>> send an initial message.
>>
>>
>> I find the `Cmd` type a little confusing, especially in the init
>> function. Conceptually, I want to "kick off" an initial fetch of data from
>> client to server, and it would make intuitive sense if I were permitted to
>> do this:
>>
>> ```
>> init : (Model, Msg)
>> init =
>> { initialModel, FetchStatus 0 }
>> ```
>>
>> But instead, the type of `init` is required to be this:
>>
>> ```
>> init : (Model, Cmd Msg)
>> init =
>> { initialModel, ... }
>> ```
>>
>> When I get to this point, I need to look up the documentation on Cmd.
>> Having read the guide several months ago, I have a vague impression that I
>> may need to "perform" something to get my message into a Cmd type. I look
>> at the `Platform.Cmd` documentation, and I see there's a `Cmd` type which
>> looks like a constructor. So I try this:
>>
>> ```
>> init : (Model, Cmd Msg)
>> init =
>> { initialModel, Cmd (FetchStatus 0) }
>> ```
>>
>> But I get an error: "Cannot find variable `Cmd`". Having some experience
>> with Elm, I believe this may mean although Cmd is a type, its constructor
>> is not exposed.
>>
>> At this point, the `map` function looks a little promising, because it
>> takes some things that are not Cmd and produces `Cmd msg`, i.e. precisely
>> the type I'm looking for. However, it's not clear to me what the first
>> parameter to map is (a function that takes `a` and produces `msg`?) There's
>> no documentation on this `map` function.
>>
>> Then I peruse the docs some more ("maybe this is so common a thing that
>> it belongs in Basics? or maybe I missed something in Platform, since Cmd is
>> a submodule of Platform?") and arrive at the Task documentation, where I
>> see the "perform" signature:
>>
>> perform
>> <http://package.elm-lang.org/packages/elm-lang/core/5.1.1/Task#perform> :
>> (a -> msg) -> Task
>> <http://package.elm-lang.org/packages/elm-lang/core/5.1.1/Task#Task>
>> Never
>> <http://package.elm-lang.org/packages/elm-lang/core/5.1.1/Basics#Never> a
>> -> Cmd
>> <http://package.elm-lang.org/packages/elm-lang/core/5.1.1/Platform-Cmd#Cmd>
>> msg
>>
>> This looks promising as well, because it takes some things and produces a
>> `Cmd msg`. But the example in the documentation shows how to use `perform`
>> with `Time.now` which further confuses things because I just want to pass a
>> Time value to my FetchStatus, like it was meant to receive (not necessarily
>> a "now" value). If I try this:
>>
>> ```
>> init : ( Model, Cmd Msg )
>> init =
>> ( initialModel, Task.perform FetchStatus 0 )
>> ```
>>
>> I get
>>
>> ```
>> Function `perform` is expecting the 2nd argument to be:
>> Task.Task Never Time
>> ```
>>
>> So finally I realize that I need to pass a "succeed" task to my `perform`
>> call so I can create a `Cmd msg` of the type I need:
>>
>> ```
>> init : ( Model, Cmd Msg )
>> init =
>> ( initialModel, Task.perform FetchStatus (Task.succeed 0) )
>> ```
>>
>> Subjectively, this all feels more convoluted than it needs to be. At a
>> basic level, I want to communicate an initial model and an initial "kick
>> off" message. It's confusing that Task types are involved in constructing
>> Cmd types. This makes finding the right documentation difficult. In
>> addition, it isn't clear why a Cmd is needed at all--why not a Msg, or a
>> List Msg? Conceptually, this would be a lower barrier to entry.
>>
>> This is just a running journal of my experience trying to do a basic Elm
>> task (no pun intended). I hope it helps make the Elm experience better in
>> some way for others.
>>
>> Best,
>> Duane
>>
>
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