(Writing to the committee rather than polluting the DT proposal thread.)

We have a bullet “Does not create a language fork” in the review criteria. I treat it like the other criteria, a fork-like proposal is a red flag, but not an automatic reject.

This relates back to our earlier conversation about proposal properties.  Eric suggested:

• Backward compatibility.  Does an extension *expand* the language or *change* it? In other words, does an extension strictly accept more programs than before, or can it change the meaning of existing programs, or even reject previously valid programs?

• Plausible default.   Do we expect the extension to eventually be on-by-default (in GHCxxxx) and effectively disappear, or will it continue to be opt-in?   -XStrict or -XRebindableSyntax are examples of an extension that we want, but that are not plausible defaults.

• Localised.  Is an extension *contained* within a module or is it *infectious*? Does my choice of extensions when writing a module affect which extensions downstream clients must enable? (I would say most extensions are contained, e.g. you can apply a type family without enabling TypeFamilies or match on a pattern synonym without enabling PatternSynonyms. However, you cannot call a function that takes an implicit parameter without enabling ImplicitParams.)

Reading our “fork-like” criterion, it seems to be saying “it’s fork-like if it is not a plausible default (in the above sense), and fork-like is bad”.  But as -XStrict and -XRebindableSyntax show, not being a plausible default isn’t necessarily bad.

Do we want to revise our language in the criteria?

Simon

From: Eric Seidel <notifications@github.com>
Sent: 09 March 2021 14:05
To: ghc-proposals/ghc-proposals <ghc-proposals@noreply.github.com>
Cc: Simon Peyton Jones <simonpj@microsoft.com>; Assign <assign@noreply.github.com>
Subject: Re: [ghc-proposals/ghc-proposals] Support ergonomic dependent types (#378)

Do we have a write up of what it means to be fork-like? Or what role the fork-like property plays in our deliberations?

We have a bullet “Does not create a language fork” in the review criteria. I treat it like the other criteria, a fork-like proposal is a red flag, but not an automatic reject.

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