GHC can't infer unlifted kind

Question

I'm running up against what looks like invalid code generated by Happy. The problem boils down to GHC not inferring a polykinded type signature for a function. Here is an example of this:

{-# Language MagicHash #-}

f x = ()

main = pure (f 1#)

Since GHC is inferring f :: a -> () where a :: *, this fails with

 • Couldn't match a lifted type with an unlifted type
   When matching the kind of ‘GHC.Prim.Int#’
 • In the first argument of ‘f’, namely ‘1#’
   In the first argument of ‘pure’, namely ‘(f 1#)’
   In the expression: pure (f 1#)

Are there any language pragmas I could just turn on to get this code to compile? I know I could in theory just add type signatures but, as this is code generated by Happy which I'd prefer not to have to manually modify anything.

Answer 1

As hinted at by @dfeuer, this is impossible. In the worst case, GHC would have to look for usages of a given function across the whole project in order to infer the levity of an argument.

This was reported as a bug in Happy and has since been fixed.