Discussion:
Proposal: Add a wrapped applicative type to Data.Monoid
Daniel Cartwright
2018-03-27 14:22:40 UTC
Permalink
I see this as being generally (as in, to the users of Haskell as a whole)
useful:

newtype Ap f a = Ap { getAp :: f a }
deriving (Applicative, Eq, Foldable, Functor, Generic, Generic1
,Monad, Ord, Read, Show, Traversable)

Some hand-written instances:
instance (Applicative f, Semigroup a) => Semigroup (Ap f a) where
(Ap x) <> (Ap y) = Ap $ liftA2 (<>) x y

instance (Applicative f, Monoid a) => Monoid (Ap f a) where
mempty = Ap $ pure mempty
Andrew Martin
2018-03-27 14:28:02 UTC
Permalink
+1 from me. I've written this type at least a dozen times in various
projects.
Post by Daniel Cartwright
I see this as being generally (as in, to the users of Haskell as a whole)
newtype Ap f a = Ap { getAp :: f a }
deriving (Applicative, Eq, Foldable, Functor, Generic, Generic1
,Monad, Ord, Read, Show, Traversable)
instance (Applicative f, Semigroup a) => Semigroup (Ap f a) where
(Ap x) <> (Ap y) = Ap $ liftA2 (<>) x y
instance (Applicative f, Monoid a) => Monoid (Ap f a) where
mempty = Ap $ pure mempty
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--
-Andrew Thaddeus Martin
David Feuer
2018-03-27 14:28:02 UTC
Permalink
I proposed same thing some time ago. The main point of contention was the
name. I hope you have better luck!
Post by Daniel Cartwright
I see this as being generally (as in, to the users of Haskell as a whole)
newtype Ap f a = Ap { getAp :: f a }
deriving (Applicative, Eq, Foldable, Functor, Generic, Generic1
,Monad, Ord, Read, Show, Traversable)
instance (Applicative f, Semigroup a) => Semigroup (Ap f a) where
(Ap x) <> (Ap y) = Ap $ liftA2 (<>) x y
instance (Applicative f, Monoid a) => Monoid (Ap f a) where
mempty = Ap $ pure mempty
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http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
Daniel Cartwright
2018-03-27 14:59:01 UTC
Permalink
I can definitely see "App" as being overloaded (Application).
Good names that I see are "Ap" and "Apply".

I think "Ap" is fine.
Post by David Feuer
I proposed same thing some time ago. The main point of contention was the
name. I hope you have better luck!
Post by Daniel Cartwright
I see this as being generally (as in, to the users of Haskell as a whole)
newtype Ap f a = Ap { getAp :: f a }
deriving (Applicative, Eq, Foldable, Functor, Generic, Generic1
,Monad, Ord, Read, Show, Traversable)
instance (Applicative f, Semigroup a) => Semigroup (Ap f a) where
(Ap x) <> (Ap y) = Ap $ liftA2 (<>) x y
instance (Applicative f, Monoid a) => Monoid (Ap f a) where
mempty = Ap $ pure mempty
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http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
Daniel Cartwright
2018-03-27 15:06:11 UTC
Permalink
One thing that I would like to respectfully point out - is that the
members' of this library mailing list end up derailing otherwise useful
conversations over the choice of a name, which is frankly a silly
bottleneck. I would much rather roll a die or flip a coin to choose a name,
and just get on to implementing the proposed thing, provided it is the case
that it is seen as generally useful.
Post by Daniel Cartwright
I can definitely see "App" as being overloaded (Application).
Good names that I see are "Ap" and "Apply".
I think "Ap" is fine.
Post by David Feuer
I proposed same thing some time ago. The main point of contention was the
name. I hope you have better luck!
Post by Daniel Cartwright
I see this as being generally (as in, to the users of Haskell as a
newtype Ap f a = Ap { getAp :: f a }
deriving (Applicative, Eq, Foldable, Functor, Generic, Generic1
,Monad, Ord, Read, Show, Traversable)
instance (Applicative f, Semigroup a) => Semigroup (Ap f a) where
(Ap x) <> (Ap y) = Ap $ liftA2 (<>) x y
instance (Applicative f, Monoid a) => Monoid (Ap f a) where
mempty = Ap $ pure mempty
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Libraries mailing list
http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
Edward Kmett
2018-03-28 09:50:09 UTC
Permalink
+1 to add it.

I don't care one way or the other about the name. =)

-Edward
Post by Daniel Cartwright
One thing that I would like to respectfully point out - is that the
members' of this library mailing list end up derailing otherwise useful
conversations over the choice of a name, which is frankly a silly
bottleneck. I would much rather roll a die or flip a coin to choose a name,
and just get on to implementing the proposed thing, provided it is the case
that it is seen as generally useful.
Post by Daniel Cartwright
I can definitely see "App" as being overloaded (Application).
Good names that I see are "Ap" and "Apply".
I think "Ap" is fine.
Post by David Feuer
I proposed same thing some time ago. The main point of contention was
the name. I hope you have better luck!
Post by Daniel Cartwright
I see this as being generally (as in, to the users of Haskell as a
newtype Ap f a = Ap { getAp :: f a }
deriving (Applicative, Eq, Foldable, Functor, Generic, Generic1
,Monad, Ord, Read, Show, Traversable)
instance (Applicative f, Semigroup a) => Semigroup (Ap f a) where
(Ap x) <> (Ap y) = Ap $ liftA2 (<>) x y
instance (Applicative f, Monoid a) => Monoid (Ap f a) where
mempty = Ap $ pure mempty
_______________________________________________
Libraries mailing list
http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
_______________________________________________
Libraries mailing list
http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
Theodore Lief Gannon
2018-03-28 11:32:04 UTC
Permalink
So it's settled, we have an `Ed` type.
Post by Edward Kmett
+1 to add it.
I don't care one way or the other about the name. =)
-Edward
Post by Daniel Cartwright
One thing that I would like to respectfully point out - is that the
members' of this library mailing list end up derailing otherwise useful
conversations over the choice of a name, which is frankly a silly
bottleneck. I would much rather roll a die or flip a coin to choose a name,
and just get on to implementing the proposed thing, provided it is the case
that it is seen as generally useful.
On Tue, Mar 27, 2018 at 10:59 AM, Daniel Cartwright <
Post by Daniel Cartwright
I can definitely see "App" as being overloaded (Application).
Good names that I see are "Ap" and "Apply".
I think "Ap" is fine.
Post by David Feuer
I proposed same thing some time ago. The main point of contention was
the name. I hope you have better luck!
Post by Daniel Cartwright
I see this as being generally (as in, to the users of Haskell as a
newtype Ap f a = Ap { getAp :: f a }
deriving (Applicative, Eq, Foldable, Functor, Generic, Generic1
,Monad, Ord, Read, Show, Traversable)
instance (Applicative f, Semigroup a) => Semigroup (Ap f a) where
(Ap x) <> (Ap y) = Ap $ liftA2 (<>) x y
instance (Applicative f, Monoid a) => Monoid (Ap f a) where
mempty = Ap $ pure mempty
_______________________________________________
Libraries mailing list
http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
_______________________________________________
Libraries mailing list
http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
_______________________________________________
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