[ghc-steering-committee] #190: Module qualified syntax, recommendation: accept

[Simon Marlow]

On Fri, 8 Mar 2019 at 09:29, Joachim Breitner <mail at joachim-breitner.de>
wrote:

> Am Freitag, den 08.03.2019, 08:55 +0000 schrieb Simon Peyton Jones via
> ghc-steering-committee:
> > My only question is: do we really need a  flag.  Suppose we simply
> > accepted the postfix “qualified” with no flag support.  Then a
> > program will be accepted that earlier compilers would have rejected –
> > and, absent a flag, we normally try to continue to reject programs
> > that weren’t legal before.  But in this case no one is going to fall
> > into this by mistake.  I suggest we consider simply allowing it as an
> > exception to our general rule, and move on.
>
> Let’s not do this. We have very few hard guidelines to help us in our
> work; “changes to the language needs a flag” is one of them. If we
> start to be lax here, we will have to justify every future flag where
> the extension would just be an invalid program otherwise, including
> things like LambdaCase etc.
>
> It is tempting, but the slope is too slippery.
>
> Most of our users (in particular the “experienced users” mentioned
> above) are used to managing a long list of flags, adding another will
> not hurt them to manage another one.
>
> And if this management becomes too long, then instead of making
> exceptions, we should either hope for Haskell20xx to liberally include
> these “convenience extensions”, or otherwise make the management of the
> extension list easier (e.g. maybe by picking up
> https://github.com/ghc-proposals/ghc-proposals/pull/92 again).
>

Yes - everything that changes the language in some way should have an
extension flag. We've been strict about this up to now, I think it would be
a shame to start making exceptions. We have the nice property that if a
module would fail to compile because it uses an extension that isn't
supported by the compiler in use, we get a useful diagnostic rather than
just a parse error. Every source file declares which language it is written
in (well, together with the .cabal file), which is a nice property to have,
and useful for other tooling in addition to compilers.

Cheers
Simon


> As for a shorter name, now about QualifiedLast?
>
>
> Cheers,
> Joachim
>
>
> --
> Joachim Breitner
>   mail at joachim-breitner.de
>   http://www.joachim-breitner.de/
>
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