Where are we on this thread, Arnaud? Separately Richard has suggested https://github.com/ghc-proposals/ghc-proposals/pull/536#issuecomment-1475395... : I think *all* extensions that just enable new syntax (without changing the
meaning of any existing programs) should be warnings.
That seems like a possible principle, which could form part of this
discussion.
Simon
On Fri, 17 Feb 2023 at 14:07, Arnaud Spiwack
Dear all,
I am to shepherd the making of our language extension policy, working off our draft document [ https://docs.google.com/document/d/1_-hPh8BRhKNlzM0dC1IRSmjCqPym9mXx9NjC7jUl... ]. As a prelude to my introduction, I first want to apologise for taking that long to get back to this subject, time has, I'm afraid, gotten away from me. Part of the reason, though, is that we've been pulling in many directions, and I felt it difficult to find a path toward consensus among all that.
In the time since I accepted the task, I have therefore spent a lot of time reading through the entire document multiple time, to try and identify the points where we agree and the points where we diverge. And try to build a methodology.
If you go to the document, you'll see that I've separated out our notes after a horizontal line. I will grow the document above the line with decisions from this mailing list. Hopefully, the process will make sure that we are in broad agreement that the text does reflect our collective position.
The way I'm going to proceed is to organise votes. Or maybe they should rather be seen as surveys. They'll have a bunch of questions, pertaining to bits of the documents that I want us to converge on. I'll extract a broad consensus from this survey, and use it to copy language in the document. I intend to give about a week for each survey to complete (conveniently, I'll be very far from a computer for the next week, so I'll be able to tally the results when I come back). It's going to take a while, but it's a very difficult, and sensitive, subject.
---
For this first round, I want us to focus on the categorisation of language extensions as proposed by Richard and Simon M (sections 2.1 and 2.3, respectively, of our draft notes). As I feel that we will need to have these categories identified in order to discuss the later points.
Here are the categories that are common to both (consult the document for more details):
1. Extensions that are either in GHC20xx or could be part of a future GHC20xx (e.g. GADTs) 2. Experimental language features (e.g. LinearTypes) 3. Extensions that allow module-wide violation of some general principle that holds elsewhere (e.g. OverlappingInstances) 4. Extensions that allow access to deprecated features (e.g. DatatypeContexts) 5. Extensions that should be compiler flags, which do not actually change the accepted language (e.g. Safe)
Richard adds another category
6. Extensions that change the semantics of existing constructs (e.g. OverloadedStrings); as opposed to most extensions, which create new syntax for the new feature.
Richard's reasoning is twofold 1/ he doesn't believe that they should be candidate for inclusion in GHC20xx 2/ he believes that they are problematic for the same sort of reason as we've used to argue against fork-like behaviour: that to understand the meaning of a piece of code you need to know what language extensions have been loaded in the file.
Simon M adds another category
7. Extensions for specialised use-cases (e.g. MagicHash, UnboxedTuples)
Simon's reasoning is that these should not be part of GHC20xx. At the very least they are not intended to. But they do extend the language, like 1, and unlike 5. Hence they deserve to be categorised separately from both.
It is worth noting that Richard classifies Strict as a 6 and Simon M classifies Strict as a 7.
Now the survey.
Keeping in mind that the goal of this categorisation is to classify the extensions that currently exist, without judgement on whether we want to have things in these categories or not:
Q1: Are all the categories 1–5 relevant? If you would like to remove some categories, which and why (free form)? Q2: Is category 6 relevant? Q2.Y: If you found category 6 to be relevant: should it be its own category, or should it be a subcategory of 1? Q2.N: If you found category 6 not to be relevant, in which category would you classify OverloadedStrings? What about PolyKinds? Q3: Is category 7 relevant? Q3.Y: If you found category 7 to be relevant: should it be its own category or should it be a subcategory of 5? Q3.N: If you found category 7 not to be relevant: in which category would you classify MagicHash? What about UnboxedTuples? Q4: In which category would you classify Strict? Q5: Is there any category that you feel is missing from the list? If so, please argue (free form).
Best, Arnaud _______________________________________________ ghc-steering-committee mailing list ghc-steering-committee@haskell.org https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee