I'm having a moment of fail trying to work out how to leave a comment.
Is there a reason (other than GHC not doing it yet) not to have do
notation use *> instead of >> in line with using the least restrictive
function? I have some otherwise-nice logic programming code that would
actively benefit from it and it seems like a missing step from here.
On 15/12/2018 23:46, Mario Blažević wrote:
The very first RFC created (https://github.com/haskell/rfcs/pull/1),
the Applicative/Monad Proposal, has now reached the Last Call stage.
In order to ground the discussion, I have taken some time to update
the Prelude and the text of the Haskell Report with its effects before
the call. The rendered report is available at
https://github.com/blamario/rfcs/blob/amp/report/report/haskell.pdf
for your review.
TL;DR:
The proposed changes to the report add the latest design of the
Applicative and Alternative classes, but otherwise are intentionally
minimal. Any further modifications, like the MonadFail proposal or
moving return out of the Monad class, should be relegated to new RFCs.
In some more detail, the changes are:
1. Applicative has been added as a subclass of Functor and superclass
of Monad, its methods and laws as currently defined in the base
library. The class and all its methods (pure, (<*>), (<*), (*>), and
liftA2) are exported from Prelude, but no other Applicative-related
functions (like liftA3) are.
2. The Functor class definition has been moved from module
Control.Monad to Control.Applicative in order to avoid circular
imports. Note that neither module is a part of the language
specification.
3. The Monad class has been left unmodified, apart from making
Applicative its superclass and adding return a == pure a as a law.
4. Alternative has been added to the Control.Applicative module, but
not to Prelude. This is the same treatment already meted to MonadPlus.
I'm unsure why MonadPlus even exists in the report, as it has no
relevance to the language specification, and I would gladly remove
both classes.
Please take some time within the following three weeks (including some
extra allowance for the upcoming holiday breaks) to vote for or
against the proposal, or to leave a comment with suggestions for its
improvement.
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