built-in typeclasses don't get replaced by the actual type like normal type variables

[Apanatshka]

Another issue to be aggregated in #1008?

Observe:

$ elm-repl
> f1 = (<)
<function> : comparable -> comparable -> Bool
> f2 = (<) 1
<function> : comparable -> Bool
> f2 "a"
As I infer the type of values flowing through your program, I see a conflict
between these two types:

    comparable

    String

Expected behaviour: f2 : number -> Bool (or perhaps Int, I don't know exactly what the compiler does there).

Original data comes from this StackOverflow question.

[evancz]

Thanks for describing this. Seems separate from #1008, looks like a bug instead. It is closer to #880 which seems to stem from the same code.

I suspect the root issue arises from this function or from this section. If someone could take a look, it may not be too crazy to find the root issue here.

[evancz]

Alright, this is resolved on the type-fixes branch which I am currently merging into master. So it'll be out with 0.16 and I'll try to do an alpha soon. Here's what I'm seeing now:

$ elm-repl
---- elm repl 0.16.0 -----------------------------------------------------------
 :help for help, :exit to exit, more at <https://github.com/elm-lang/elm-repl>
--------------------------------------------------------------------------------
> (<)
<function> : comparable -> comparable -> Bool
> isNegative n = n < 0
<function> : number -> Bool
> isPositive = (<) 0
<function> : number -> Bool
>