SPECIALISE entry in manual says it's not available
https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/exts/rewrite_rules.html?highlight=specialise#specialisation says that SPECIALISE
no longer exists. But it does exist! The correct documentation is here: https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/exts/pragmas.html?highlight=pragmas#specialize-instance-pragma