Re: [ghc-steering-committee] Amend or patterns (#522) to use p1 ; p2 (#609)

In favor On Fri, Sep 8, 2023 at 6:36 PM Simon Peyton Jones < simon.peytonjones@gmail.com> wrote:

I don't have a strong opinion here. The authors have done a pretty diligent job of exploring syntactic alternatives, and seeking feedback from the community. I'm quite content to accept this proposal. (We have already accepted the base or-pattern proposal, so that's not our subject for debate.)

Simon

On Fri, 8 Sept 2023 at 03:57, Chris Dornan wrote:

...

Proposal: Amend or patterns (#522) to use p1 ; p2 (#609) Author: Sebastian Graf, David Knothe Rendered proposal: https://github.com/ghc-proposals/ghc-proposals/blob/eb4b67c29282520b2c5c6a49... Discussion: https://github.com/ghc-proposals/ghc-proposals/pull/609 Recommendation: Acceptance

## Summary

This proposal refines the syntax of an already accpted proposal (#522) for writing or patterns.

The syntax of the old proposal,

```haskell stringOfT :: T -> Maybe String stringOfT (T1 s) = Just s stringOfT (one of T2{}, T3{}) = Nothing ```

is replaced with

```haskell stringOfT :: T -> Maybe String stringOfT (T1 s) = Just s stringOfT (T2{}; T3{}) = Nothing ```

or indeed

```haskell stringOfT :: T -> Maybe String stringOfT x = case x of T1 s -> Just s T2{} T3{} -> Nothing ```

(Beacuse the '(' ... ')' are optional here, we can remove them and naturally exploit layout.)

The authors have conducted polls to see what folks preferred, landing on this proposal. The adjustments to the Haskell grammar are really quite minimal requiring one extra production.

## Recommendation

The proposal is nondiruptive and as a whole addresses an important practical topic. I recommend that we accept it

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