#13733: Simplify constraints on RULES LHS -------------------------------------+------------------------------------- Reporter: nomeata | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by nomeata): Another view is that the problem is that the user cannot even specify the desired rule, namely one that matches {{{ GHC.Classes.$fEq[]_$c== @ Integer GHC.Integer.Type.$fEqInteger }}} and maybe the problem should be attacked from this angle. There is precedent in the way `coerce` works on the LHS of a rule: If it appears on the LHS, the compiler assumes the user wants to match any Core- level cast (`x |> c`), and thus inlines `coerce`, and even changes the free variable of the rule so that it can match unlifted coercions (see Note [Getting the map/coerce RULE to work]). In that sense, solving constraints on the LHS is not really monkeying or a plaster, but it is what what we have to do to allow the user to write rules that match a specific instance method. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13733#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler