Regarding underspecified: I think that's appropriate at this phase. The main proposal is: maybe FilePath an abstract type. It will take multiple GHC releases before we switch over fully, with plenty of time to hash out details of how the filepath package should work, and the opportunity to experiment with different wrappers around a core abstract type.

Having used an alternate FilePath type for a while (via system-filepath), I can say that it doesn't give the same benefit of just fixing the central FilePath type. Having to convert between types all over the place is tedious, defeats a lot of the performance benefits we're going for, and hurts type safety.

As someone who typically is very much opposed to breaking changes in core libraries: I think this one is well worth it.

On Mon, Jun 29, 2015 at 11:39 AM Erik Hesselink <hesselink@gmail.com> wrote:

I think this proposal is currently underspecified. For example, it's
not clear to me what the semantics of a FilePath are. I have the
feeling that `toFilePah` should return a Maybe, for example, but it's
hard to say without knowing what it's converting to, exactly.

I also worry about the immense breakage this will cause. This is not
just an issue of causing a lot of work for maintainers, but also of
lots of unmaintained libraries, printed code etc breaking. I feel that
there is not enough gain in this proposal relative to the amount of
breakage.

Has any thought been given to introduce new modules for this type, and
leave the old ones in place?

Erik

On Fri, Jun 26, 2015 at 6:08 PM, Herbert Valerio Riedel <hvr@gnu.org> wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> Hello *,
>
> What?
> =====
>
> We (see From: & CC: headers) propose, plain and simple, to turn the
> currently defined type-synonym
>
> type FilePath = String
>
> into an abstract/opaque data type instead.
>
> Why/How/When?
> =============
>
> For details (including motivation and a suggested transition scheme)
> please consult
>
> https://ghc.haskell.org/trac/ghc/wiki/Proposal/AbstractFilePath
>
>
>
> Suggested discussion period: 4 weeks
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