Type Classes in Elm

Yeah, but you can do the pattern the same way scala does, just manually

so how does show work in elm

type alias ShowOps a =
    { show : a -> String }


show : ShowOps a -> a -> String
show ops a =
    ops.show a


stringShowOps : ShowOps String
stringShowOps =
    { show = identity }


intShowOps : ShowOps Int
intShowOps =
    { show = String.fromInt }


listShowOps : ShowOps a -> ShowOps (List a)
listShowOps elementShowOps =
    { show = \l -> "[ " ++ String.join ", " (List.map (show elementShowOps) l) ++ " ]" }


x : String
x =
    show (listShowOps intShowOps) [ 1, 2, 3 ]

Like this.

It's literally the same as scala except there are no implicit parameters - at which point you start to realize that maybe its not that special a pattern.

well

obviously.

it's the implicit parameters that is the special part

sure, but the point is if i want to take a parameter that is Show, I just need access to the functions

well... yes that's kinda how vtables work too?

Yep, it's all connected. You want "dynamic dispatch" in a strongly typed system with no interface polymorphism? Make a vtable, pass it around.

<- Index