seeing
aexp -> qvar (variable)
| gcon (general constructor)
...
| qcon { fbind1 … fbindn } (labeled construction)
| aexp { fbind1 … fbindn } (labelled update)
and
https://www.haskell.org/onlinereport/haskell2010/haskellch3.html#x8-220003
I realise that the update requires at least one field binding whereas
for a construction "C {}" (n = 0) could be used. ("C {}" makes sense
for patterns!)
And due to the meta-rule a labelled update is not possible for a lambda
abstraction, let expression, or conditional (as aexp), but it is for
case (and do if the record type happens to be a monad). So a further
less obvious example is:
case e of
p -> r
{ f = v }
that will be parsed as: (case e of p -> r) { f = v }
(I'm sure the grammar could be fully disambiguated, but this would not
improve readability. Preferring shift over reduce is common and fine for
such cases.)
Cheers Christian
Am 12.07.2016 um 10:36 schrieb Simon Peyton Jones via Glasgow-haskell-users:
> I've added record construction and update to the syntax, which makes it
> clearer how the other constructs are analogous to them.
>
> Simon
>
> | -----Original Message-----
> | From: Glasgow-haskell-users [mailto:glasgow-haskell-users-
> | boun...@haskell.org] On Behalf Of Akio Takano
> | Sent: 11 July 2016 03:24
> | To: glasgow-haskell-users@haskell.org
> | Subject: ArgumentDo proposal updated
> |
> | Hi glasgow-haskell-users,
> |
> | Thank you for all the feedback to the ArgumentDo proposal. Following
> | the discussion, I made changes to the proposal and updated the wiki
> | page [0].
> |
> | Now the proposed grammar is greatly simplified: it doesn't add a new
> | non-terminal anymore, indeed it removes one instead. The proposed set
> | of accepted programs remains unchanged.
> |
> | I hope the this update addresses one major concern that was raised in
> | the previous discussion.
> |
> | Any feedback is appreciated.
> |
> | Regards,
> | Takano Akio
> |
> | [0]: https://ghc.haskell.org/trac/ghc/wiki/ArgumentDo
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