Reproducer for GHC bug #24934.
To reproduce, run the following:
ghc -O1 T24934a.hs T24934b.hs Main.hs
./Main
Main: internal error: Oops! Entered absent arg Arg: $d~
Type: RepDim (F i 2) ~ 2
In module `T24934b'
Please report this as a GHC bug: https://www.haskell.org/ghc/reportabug