[ghc-steering-committee] Proposal #302: Multiway lambda: time to vote

[Eric Seidel]

On Mon, Jul 19, 2021, at 05:53, Simon Peyton Jones via ghc-steering-committee wrote:
> 2. (2) and (4) seem to lose \case{}, which is useful in practice. Am I 
> correct in saying that we'll lose \case{}?
>  
> Yes that too is true, and is a strike against (2) and (4).

I'm confused, the proposal explicitly says

> If no clauses are given, i.e. the expression in question if \case {}, how many arguments this expression should take is ambiguous. However, currently, with -XEmptyCase, this expression is already valid and takes a single argument. Thus, to maintain backwards compatibility and for lack of a better option, this proposal does not alter the behavior of this expression.

https://github.com/JakobBruenker/ghc-proposals/blob/patch-1/proposals/0000-lambda-layout.md#alternative-2-comma-separated-case

What's the problem with this solution? \case {} can still be instantiated at any arity, but it will explode after applying a single argument.