Hello. The compiler gives here correct message. Because your messageParam can
be anything of type Message. Lodash(_) in Elm means the same. So it means
anything with type Message. That’s why you have two same branches. And Elm
compiler tells you about it.
Best,
Andrey
> On 10 Jul 2017, at 20:11, Patrick Stubner <pstub...@gmail.com> wrote:
>
> I haven't really used Elm that much, but you may want something like this:
>
>
> module Main exposing (..)
>
> import Html exposing (Html, text, div)
>
> type Message = Good | Bad | ManyOthers
>
> type alias Node = { message : Message }
>
> trymatch : Node -> Message -> Bool
> trymatch node messageParam =
> node.message == messageParam
>
> evalTrue = trymatch { message = Good } Good
> evalFalse = trymatch { message = Good } Bad
>
> main : Html a
> main =
> div []
> [ text (toString evalTrue)
> , text " / "
> , text (toString evalFalse)]
>
>
> You can try it out in https://ellie-app.com
>
> P@
>
>
> Am Sonntag, 9. Juli 2017 22:55:27 UTC+2 schrieb jadski:
> Hi, I am getting a compiler error that does not make sense to me - can anyone
> help to explain why this fails to compile?
>
> The following code:
>
> <code>
> type Message = Good | Bad | ManyOthers
>
> type alias Node = { message : Message }
>
> trymatch : Node -> Message -> Bool
> trymatch node messageParam =
> case node.message of
> messageParam ->
> True
> _ ->
> False
>
> evalTrue = trymatch { message = Good } Good
> evalFalse = trymatch { message = Good } Bad
> </code>
>
> Generates this compilation error:
>
> <code>
> The following pattern is redundant. Remove it.
>
> 10| _ ->
> ^
> Any value with this shape will be handled by a previous pattern.
> </code>
>
> However node.message and messageParam can clearly be different, as in
> evalFalse.
>
> Hence the message "Any value with this shape will be handled by a previous
> pattern." appears incorrect, and is confusing me.
>
> A helpful slacker suggested using "if node.message == messageParam then",
> which compiles, but doesn't clarify what's going wrong here.
>
>
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