#7169: Warning for incomplete record field label used as function -------------------------------------+------------------------------------- Reporter: goldfire | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.7 Resolution: | Keywords: Warnings, | newcomer Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect | Unknown/Multiple warning at compile-time | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): I agree with nakaji-dayo here. Emitting a warning upon every use of `quux` feels like the wrong design choice. To address goldfire's point above:
We want to be able to have fields such as `quux` that are used only with some (but not all) constructors of a type
I agree. I think a reasonable design would be: * Introduce a flag for this purpose (proposal: `-Wpartial-records`) * If the flag is enabled and you define a partial record selector (e.g., `data A = B1 { b :: Int } | B2 { b :: Int, wat :: Char }`, emit a warning of the definition site (and only the definition site). * One can disable this warning by prefixing the partial record selector with an underscore (e.g., `data A = B1 { b :: Int } | B2 { b :: Int, _wat :: Char }`). This should allow you to use the partial record for scenarios where it's handy, but it also gives a visual indication that something is fishy about that function. A separate question is if this flag should be implied by `-Wall`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/7169#comment:17 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler