#12224: Replace placeHolderPunRhs with a PlaceHolder value -------------------------------------+------------------------------------- Reporter: alanz | Owner: alanz Type: task | Status: new Priority: normal | Milestone: 8.2.1 Component: Compiler | Version: 8.0.1 (Parser) | 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 alanz): I tried that, but get {{{ compiler/hsSyn/HsPat.hs:331:57: Couldn't match expected type ‘PostRn id b’ with actual type ‘b’ ‘b’ is a rigid type variable bound by the type signature for fmap :: (a -> b) -> HsRecField' id lbl a -> HsRecField' id lbl b at compiler/hsSyn/HsPat.hs:331:3 Relevant bindings include a :: PostRn id a (bound at compiler/hsSyn/HsPat.hs:331:25) f :: a -> b (bound at compiler/hsSyn/HsPat.hs:331:8) fmap :: (a -> b) -> HsRecField' id lbl a -> HsRecField' id lbl b (bound at compiler/hsSyn/HsPat.hs:331:3) In the second argument of ‘HsRecField’, namely ‘(f a)’ In the expression: HsRecField ln (f a) p }}} I had to bring in an `id` separate from the `lbl` to get the `Data` instances to come out. My interpretation of the error message is that it is impossible to define `fmap` for this type. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12224#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler