[ghc-steering-committee] Proposal #302: `\of`

[Simon Marlow]

Cale's rationale chimes with me. A lot - I feel like I might have even made
the same point in previous threads on this. I think of the tradeoff like
this:

* The lack of \of doesn't really hurt very much. In fact, arguably by
forcing the author to type some more characters and give something a name,
we get code that's clearer for the reader. (yes this is very subjective,
but syntax is).
* The addition of \of *would* hurt new users of the language. Only a bit,
but every bit makes things worse, and things are already quite bad.

Cheers
Simon

On Thu, 3 Sep 2020 at 23:02, Richard Eisenberg <rae at richarde.dev> wrote:

> Hi all,
>
> Proposal #302 was submitted to the committee and assigned to Cale. He has
> made a recommendation on the GitHub trail, but I don't believe the
> committee has discussed this among ourselves.
>
> PR: https://github.com/ghc-proposals/ghc-proposals/pull/302
> Proposal:
> https://github.com/JakobBruenker/ghc-proposals/blob/patch-1/proposals/0000-lambda-layout.md
> Cale's recommendation:
> https://github.com/ghc-proposals/ghc-proposals/pull/302#issuecomment-666075014
>
> The idea, in brief, is to introduce a new syntax (guarded behind
> -XMultiWayLambda) \of. Here is an example, which gives you the idea:
>
> mplus :: Maybe Int -> Maybe Int -> Maybe Int
> mplus = \of
>   Nothing _ -> Nothing
>   _ Nothing -> Nothing
>   (Just x) (Just y) -> Just (x + y)
>
> The new keyword allows us to use a syntax similar to function definitions,
> but without repeating the name of the function. It is also like \case, but
> it allows multiple arguments. Guards are allowed, as usual.
>
> I really like this new syntax -- mostly because I find it very strange
> that we have to repeat the function name on every line. And then change the
> spacing when we change the function name. And I like the mnemonic "lambda
> of". And it allows me to write a where clause that is accessible in
> multiple different patterns, or an indented where clause that is usable in
> just one. If it didn't confuse readers, I would use this syntax all the
> time.
>
> Even so, I agree with Cale's recommendation to reject. We just have too
> much syntax! If someone were to come along and draft a concrete proposal of
> how we could, for example, use this syntax to replace both \case and if|,
> with a migration strategy, etc., then I might be in favor. Until then, I
> think we've spent our budget for cute, obscure bits of syntax.
>
> Richard
> _______________________________________________
> ghc-steering-committee mailing list
> ghc-steering-committee at haskell.org
> https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.haskell.org/pipermail/ghc-steering-committee/attachments/20200917/504de857/attachment.html>