Compiler: Type is not checked after a function references itself

[hecrj]

I have found a weird type-checking issue after self-referencing a function in Elm 0.19. The following code compiles and produces a runtime error:

module Main exposing (main)

import Html exposing (Html)


sscce : a -> Html msg
sscce anything =
    let
        thisDefinitionBreaksThings =
            sscce
    in
    anything "whoops!" "This should not compile" 3 4 112 () []


main : Html msg
main =
    sscce ()

This same example does not compile in Elm 0.18, producing the expected error:

`anything` is not a function, but you are giving it 7 arguments!

Maybe you forgot some parentheses? Or a comma?

It looks like Elm stops type-checking anything after the function references itself and then allows me to do whatever I want with it (?).

[G4BB3R]

I simplified this SSCCE:

module Main exposing (main)

import Html

f : a -> Html.Html b
f a =
    a f

main =
    f ()

If I remove the type definition of f, it won't compile and show the correct error.

But with the type definition it crashes at runtime.

[evancz]

Both of these SSCCEs are really excellent! Thank you!

With the changes in https://github.com/elm/compiler/commit/af37341a2969ed5a8391adb95cf094e24673c2d7, I am getting the following errors for the examples you provided:

-- TOO MANY ARGS ------------------------------------------------------ temp.elm

The `anything` value is not a function, but it was given 7 arguments.

8|     anything "whoops!" "This should not compile" 3 4 112 () []
       ^^^^^^^^
Are there any missing commas? Or missing parentheses?

-- TOO MANY ARGS ------------------------------------------------------ temp.elm

The `a` value is not a function, but it was given 1 argument.

16|     a f
        ^
Are there any missing commas? Or missing parentheses?