ArgumentDo proposal updated

[C Maeder]

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-
> |  bounces at haskell.org] On Behalf Of Akio Takano
> |  Sent: 11 July 2016 03:24
> |  To: glasgow-haskell-users at 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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