Dict should require comparable and Dict.get error messages can be more specific

[showell]

Here is the code that doesn't compile:

import Dict exposing (Dict)

type Fruit
    = Apple
    | Banana

type alias SimpleTuple =
    (Fruit, Int, Bool)

type alias SimpleDict =
    Dict SimpleTuple String

f : Fruit -> SimpleDict -> Maybe String
f fruit dct =
    Dict.get (fruit, 42, False) dct

Here is the error:

The 1st argument to `get` is not what I expect:

15|     Dict.get (fruit, 42, False) dct

                 ^^^^^^^^^^^^^^^^^^
This argument is a tuple of type:

    ( Fruit, number, Bool )

But `get` needs the 1st argument to be:

    comparable

Hint: I only know how to compare ints, floats, chars, strings, lists of
comparable values, and tuples of comparable values.

The deeper problem here is that this is legal in Elm:

type alias SimpleDict =
    Dict SimpleTuple String

If the above were illegal (i.e. Dict was Dict comparable v instead of Dict k v), I probably would have gotten a useful error as soon as I tried to compile the type.

The more immediate problem is that the error message is too vague. It tells me ( Fruit, number, Bool ) is not a comparable. It could more specifically tell me that Fruit is not a comparable.

Thanks!