#14279: Type families interfere with specialisation rewrite rules -------------------------------------+------------------------------------- Reporter: IvanTimokhin | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Resolution: | Keywords: TypeFamilies Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: Other | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by goldfire): I argue that (related to my musings in #14119), patterns -- such as that LHS of rules -- should not mention type families at all. In other words, we should change any `F ty` in rule LHS to a fresh type variable `a` and then require `F ty ~ a`. Which, as it turns out, is precisely what's done in my [http://cs.brynmawr.edu/~rae/papers/2017/partiality/partiality.pdf Constrained Type Families] paper. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14279#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler