Erroneous type errors with higher-order functions

[jazullo]

Consider the following:

fix :: ((a -> b) -> a -> b) -> a -> b
fix f x = f (\y -> fix f y) x

fac :: Int -> Int
fac x = fix (\go n -> if n > 0 then n * go (n-1) else 1) x

This typechecks under GHC, but Gibbon yields the following error:

gibbon: arrIns: Not an arrow type: ForAll [] (MetaTv (Meta 23))
CallStack (from HasCallStack):
  error, called at src/Gibbon/L0/Syntax.hs:305:14 in gibbon-0.2-inplace:Gibbon.L0.Syntax

Note that fix can successfully typecheck on it's own, but typechecking it's application is bugged. I think this is an issue with higher-order functions in general rather than a fixpoint function specifically, another example of this would be helpful.