On Wed, Jan 25, 2017 at 8:17 AM, Maksim Demin <[email protected]> wrote:
> Thanks for the response, it totally works, and I definitely think it is
> cleaner than having to Html.map everything! I am still trying to fully
> understand what is going on, pretty new to Elm. I kinda get what you are
> doing in the update to map the command,
>
> ( { model | field2 = "2" }, Cmd.map cfg.lift pageTwoCmd )
>
> but how does that happen in the view? How does this cfg.lift which is lift
> : Page1Msg -> msg work here?
>
> div [ onClick (cfg.lift <| DoSomething1) ] [ text model.field2 ]
>
Sorry about that, my bad. It should have been
div [ onClick (cfg.lift DoSomething1) ] [ text model.field2 ]
basically, the view receives a function that knows how to lift the messages
of the SubModule to the message of the parent. If you have type defined as
type Msg
= Msg1 Page1Msg
Msg1 is also a value constructor, in other words, a function that takes a
Page1Msg and outputs a Msg. This is why you can use it as cfg.lift
Now, the reason my code looked like that was because it started as:
div [ onClick (cfg.lift << DoSomething1) ] [ text model.field2 ]
and when I saw that not working, my mind produced the version with the <|
(my mind is weird sometimes)
You need << (function composition) when the event handler receives a
function.
So, if you have a submodule message like `type Msg = UpdateNameField
String` and in the view you have an input event, it would look like
input [onInput (cfg.lift << UpdateNameField)] []
if cfg.lift is *f* and UpdateNameField is *g*, then (cfg.lift <<
UpdateNameField) is *h* so that h(a) = f(g(a))
I remember being new to Elm and finding function application (*<|* and* |>*
) and function composition ( *<<* and *>>*) mystifying.
After seeing few more examples and reading through these functions
documentation
<http://package.elm-lang.org/packages/elm-lang/core/5.1.1/Basics#<|> my
mind clicked and now I love them.
They can make the code very very readable.
--
There is NO FATE, we are the creators.
blog: http://damoc.ro/
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