[RFC] Qualified module renamings

Bryan Richter b at chreekat.net
Thu Feb 25 18:06:12 UTC 2021


It took me about five minutes to arrive at the guess that this is about the
syntax in Cabal files for using backpack - is that right?

What is the intent of what got implemented, anyway? Are there example use
cases?

Den tors 25 feb. 2021 18:14Edward Z Yang <ezyang at mit.edu> skrev:

> Today, using the 'mixins' field you can rename modules that come from
> other packages by manually expressing a renaming one-by-one. In some
> Backpack use cases, you may have a lot of modules that you would like to
> mechanically rename into some subnamespace; today, you have manually list
> each renaming one by one.
>
>
> https://github.com/haskell/cabal/pull/7303 contains an implementation of
> one possible way to extend mixin syntax to support qualified renaming; the
> implementation is very simple. The syntax here is based off of Richard
> Eisenberg's local modules proposal (
> https://github.com/ghc-proposals/ghc-proposals/pull/283) which supports
> the qualified keyword before module exports/imports which has the same
> effect (bring the module into scope under a sub-module namespace). However,
> the PR isn't really meant to be an end all to the discussion: it's just to
> show that it's pretty simple to implement this functionality.
>
>
> There are two primary axes which I am looking for feedback:
>
>
> * Expressivity. The current PoC implementation only permits
> unconditionally prefix-ing all modules that would have been brought into
> scope by the mixin; e.g., transforming module A to Prefix.A. Edward Kmett
> has expressed that in some cases, he would like it if you could implement
> the import as a suffix. One could also imagine allowing arbitrary string
> transformations. Opinions on where to draw the line for expressivity are
> solicited.
>
>
> * Syntax. The current syntax is "pkgname qualified Prefix" as it is
> symmetric with "pkgname hiding (A, B)" and it was simple to implement. But
> I am not particularly attached to this syntax, and am open to other
> suggestions. If we permit suffixing, a wildcard based syntax like "pkgname
> (* as *.Suffix)" may be preferable (though modestly more complex to specify
> and implement; for example, is the glob recursive over dots?). Edward Kmett
> has offered some other possibilities at
> https://github.com/haskell/cabal/issues/7290#issue-812744575‚Äč
>
>
> Thanks Oleg for reminding me to send this RFC to this mailing list.
>
>
> Cheers,
>
> Edward
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