#12229: Narrow the scope of record wildcards notation slightly -------------------------------------+------------------------------------- Reporter: simonpj | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 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 simonpj): Interestingly, at least some of the things that are now rejected were ALSO rejected before, in a different and more confusing way. Consider {{{ module T12229 where data T = MkT { x, pi :: Float } f x = MkT { .. } -- 'pi' is not initialised, because -- there is no local binding }}} Previously the record-wildcard expansion said "oh, there is one `pi` in scope that isn't a record selector, so fine, let's expand it"; so we got {{{ f x = MkT { x = x, pi = pi } }}} But THEN we got (from 7.10) {{{ T12229 .hs:7:7: Ambiguous occurrence ‘pi’ It could refer to either ‘T12229.pi’, defined at T12229.hs:5:19 or ‘Prelude.pi’, imported from ‘Prelude’ at T12229.hs:3:8-19 (and originally defined in ‘GHC.Float’) }}} which is stupid and confusing. With our new change we get {{{ T12229.hs:7:7: warning: [-Wmissing-fields (in -Wdefault)] Fields of ‘MkT’ not initialised: pi In the expression: MkT {..} In an equation for ‘f’: f x = MkT {..} }}} which is better. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12229#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler