Moving ArgumentsDo forward

Edward Kmett ekmett at
Wed Jun 1 16:32:46 UTC 2016

Just as a note: I noticed this was being discussed a couple of weeks ago as
a possible topic for haskell-prime, when they were discussing what was in
scope for the committee, so I'm not entirely sure its a dead topic.


On Wed, Jun 1, 2016 at 11:09 AM, Bardur Arantsson <spam at>

> On 06/01/2016 01:48 PM, Akio Takano wrote:
> > Hi,
> >
> > Ticket #10843 [0] proposes an extension, ArgumentsDo, which I would
> > love to see in GHC. It's a small syntactic extension that allows do,
> > case, if and lambda blocks as function arguments, without parentheses.
> > However, its differential revision [1] has been abandoned, citing a
> > mixed response from the community. A message [2] on the ticket
> > summarizes a thread in haskell-cafe on this topic.
> >
> > I, for one, think adding this extension is worthwhile, because a
> > significant number of people support it. Also, given how some people
> > seem to feel ambivalent about this change, I believe actually allowing
> > people to try it makes it clearer whether it is a good idea.
> >
> > Thus I'm wondering: is there any chance that this gets merged? If so,
> > I'm willing to work on whatever is remaining to get the change merged.
> >
> What's changed since it was last discussed? I don't think the objections
> were centered in the implementation, so I don't see what "whatever is
> remaining to get the change merged" would be.
> AFAICT at best it's a *very* small improvement[1] and fractures Haskell
> syntax even more around extensions -- tooling etc. will need to
> understand even *more* syntax extensions[2].
> Regards,
> [1] If you grant that it is indeed an improvment, which I, personally,
> don't think it is.
> [2] I think most people agree that this is something that should perhaps
> be handled by something like
> so that it would only need
> to be implemented once, but there's not even an alpha release yet, so
> that particular objection stands, AFAICT.
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