Re: [ghc-steering-committee] Wrapping up Constructor Synonyms and Pattern Synonym Signatures

Your suggestions were most helpful anyone. Joachim, the wording you chose especially helped, thank you! Here are my proposed replies to #41 and #42: #41: This proposal is rejected as it abandons the syntactic distinction between constructors and the benefits described don't justify the loss. #42: This proposal is being accepted with some provisions. - The modifications should not change the behavior of existing pattern synonyms that have not specified a type signature. - The proposal doesn't address the relationship between signatures of the constructor and the signature of the pattern. The options discussed in order of most conservative to least were: * May not differ in anything but the constraints. * Must have the same return type. * Must have the same outer type constructor in their return type. * No relation. The committee chose the first, most restricted, variant to follow the principle of least surprise. If there's a strong belief that the looser relationships may be useful, those can be described in a new proposal. If there are no objections I will comment upon and close #41, comment on #42, and then merge #42. Thank you again everyone, Chris On Thu, Apr 13, 2017 at 3:06 AM, Simon Marlow wrote:

Agree, I'm in favour of the conservative version of #42 and against #41.

But #42 also has a proposal for inference of the constructor type in the absence of a type signature, and gives several options there. I presume we want to be conservative and say that we're not making any changes to the behaviour in the absence of a type signature, right?

Cheers Simon

On 9 April 2017 at 21:16, Christopher Allen wrote:

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Thank you to those of you that replied. I'd like to preserve the syntactic distinction that construction synonyms eliminates. Your statements have shifted me to a reject on https://github.com/ghc-proposals/ghc-proposals/pull/41

If no one has objections, I'd like to move to a reject as I think enough time has elapsed that it's unlikely to get any defenders. Speak up if you feel something was missed.

Regarding https://github.com/ghc-proposals/ghc-proposals/pull/42

Summarizing peoples' replies so far:

Joachim: In favor, as long as :i does the right thing. Seems under-specified, suggested the following possible relationships between signature of the pattern and the constructor:

* May not differ in anything but the constraints. * Must have the same return type. * Must have the same outer type constructor in their return type. * No relation.

Roman: In favor of this proposal under the "May not differ in anything but the constraints" policy and against it under any of the other three.

Simon PJ: In favor of #42 alone, but no holes. Agrees with Roman that that type of the constructor should be the same as that of the pattern.

Simon Marlow: I believe the statement was in favor of #42 contra #41, but I didn't get a sense of how strongly or how Simon felt about the particulars.

I agree with and want to highlight Roman's point regarding,

...

A looser relationship between the constructor function and the pattern makes code significantly harder to read and the proposal doesn't include any justification for such a looser relationship so I would go with the strongest requirement possible.

It seems to me like the respondents so far are in favor of #42, but want the strongest variant. I'd like to move to accept #42 with the "May not differ in anything but the constraints" variant. Any objections?

Thank you Joachim for the status update last week.

Thanks you for your time everyone, Chris Allen _______________________________________________ ghc-steering-committee mailing list ghc-steering-committee@haskell.org https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee

-- Chris Allen Currently working on http://haskellbook.com