#11482: Turn -fdefer-typed-holes on by default -------------------------------------+------------------------------------- Reporter: thomie | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect | Unknown/Multiple warning at compile-time | Test Case: Blocked By: | Blocking: Related Tickets: #9497, #11481 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by thomie): * failure: None/Unknown => Incorrect warning at compile-time @@ -24,1 +24,1 @@ - use typed holes, which does show a warning (unless explicitly suppressed + use typed holes, which do show a warning (unless explicitly suppressed New description: From http://www.devalot.com/articles/2013/07/why-haskell.html: You can, however, return an `undefined` value which when evaluated will terminate the program. Haskell programmers use this to stub out parts of the program during development and they’re easy to detect during a production build.↩ That's terrible, they should be using [https://downloads.haskell.org/~ghc/7.10.3/docs/html/users_guide/typed- holes.html typed holes]! Hypothesis: because `ghc -fdefer-typed-holes Test.hs` is annoying to type, haskellers currently reach for `undefined` instead of typed holes (i.e. `_`), to mark the part of their code that isn't finished yet. Richard writes in ticket:9497#comment:2: I'm -1 on [enabling -fdefer-typed-holes by default]. It seems to invite the possibility that holes could make their way into released code. That's true, but the alternative is worse: developers keep using `undefined` instead of typed holes. Since ghc doesn't show any warnings for using `undefined` (#8064), we should make it as easy as possible to use typed holes, which do show a warning (unless explicitly suppressed with `-fno-warn-typed-holes`). Having to specify a command-line flag is too high a barrier (since `undefined` is so well known and easy to use) Proposal: * ghc turns `-fdefer-typed-holes` on by default. * build scripts specify `-fno-defer-typed-holes` to make sure no holes make it into releases. * we encourage everyone to use `_` instead of `undefined`. -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11482#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler