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Corentin Dupont

16 Aug 2016 16 Aug '16

2:21 p.m.

Hi guys, is there some library with a Monad (+Applicative, Functor...) instance of the following type: data Todo a b = Todo [a] | Done b Thanks! Corentin

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Francesco Ariis

16 Aug 16 Aug

2:21 p.m.

New subject: Todo monad

On Tue, Aug 16, 2016 at 08:21:31PM +0200, Corentin Dupont wrote:

...

Hi guys, is there some library with a Monad (+Applicative, Functor...) instance of the following type:

data Todo a b = Todo [a] | Done b

What is the general idea behind the "todo monad"? As an unrepented procrastinator, I might learn something useful.

Mihai Maruseac

2:35 p.m.

New subject: Todo monad

You could say that yak shaving is bind, you just get more stuff on the "todo list". On Tue, Aug 16, 2016 at 2:21 PM, Francesco Ariis wrote:

...

On Tue, Aug 16, 2016 at 08:21:31PM +0200, Corentin Dupont wrote:

...
Hi guys, is there some library with a Monad (+Applicative, Functor...) instance of the following type:

data Todo a b = Todo [a] | Done b

What is the general idea behind the "todo monad"? As an unrepented procrastinator, I might learn something useful. _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

-- Mihai Maruseac (MM) "If you can't solve a problem, then there's an easier problem you can solve: find it." -- George Polya

Jules Mazur

2:41 p.m.

New subject: Todo monad

Honest question -- why use this over e.g. a callback function? The point of this structure, as I understand it, would be to establish the status of asynchronous computations being performed from `[a]`; it follows that this status would be used to execute a follow-up computation. Jules On Aug 16 2016, at 2:27 pm, Francesco Ariis wrote:

...

On Tue, Aug 16, 2016 at 08:21:31PM +0200, Corentin Dupont wrote: Hi guys, is there some library with a Monad (+Applicative, Functor...) instance of the following type:

data Todo a b = Todo [a] | Done b

...

What is the general idea behind the "todo monad"? As an unrepented

procrastinator, I might learn something useful. _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

eyeinsky .

17 Aug 17 Aug

2:01 a.m.

New subject: Todo monad

For sure you need to be able to add stuff to the todo list ;) On Aug 16, 2016 8:27 PM, "Francesco Ariis" wrote:

...

On Tue, Aug 16, 2016 at 08:21:31PM +0200, Corentin Dupont wrote:

...
Hi guys, is there some library with a Monad (+Applicative, Functor...) instance of the following type:

data Todo a b = Todo [a] | Done b

What is the general idea behind the "todo monad"? As an unrepented procrastinator, I might learn something useful. _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

David Kraeutmann

16 Aug 16 Aug

2:23 p.m.

This looks functionally identical to type Todo a b = Either [a] b, and Either has a Monad instance. On 8/16/2016 8:21 PM, Corentin Dupont wrote:

...

Hi guys, is there some library with a Monad (+Applicative, Functor...) instance of the following type:

data Todo a b = Todo [a] | Done b

Thanks! Corentin

_______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

David Kraeutmann

5:12 p.m.

I went from the assumption that he just wants something like instance Monad (Todo a) and that implies that b is the type inside of the monad. On 08/16/2016 08:23 PM, David Kraeutmann wrote:

...

This looks functionally identical to type Todo a b = Either [a] b, and Either has a Monad instance. On 8/16/2016 8:21 PM, Corentin Dupont wrote:

...
Hi guys, is there some library with a Monad (+Applicative, Functor...) instance of the following type:

data Todo a b = Todo [a] | Done b

Thanks! Corentin

_______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

_______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

David Kraeutmann

5:25 p.m.

...

I have a hunch that the desired behavior is Either b [a], tho. (Or

This was in reply to Theodore's message: possibly [Either b a]?) On 08/16/2016 11:12 PM, David Kraeutmann wrote:

...

I went from the assumption that he just wants something like

instance Monad (Todo a)

and that implies that b is the type inside of the monad.

On 08/16/2016 08:23 PM, David Kraeutmann wrote:

...
This looks functionally identical to type Todo a b = Either [a] b, and Either has a Monad instance. On 8/16/2016 8:21 PM, Corentin Dupont wrote:

...
Hi guys, is there some library with a Monad (+Applicative, Functor...) instance of the following type:

data Todo a b = Todo [a] | Done b

Thanks! Corentin

_______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

_______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

Corentin Dupont

5:56 p.m.

That, right, just to clarify, my instances are like that: instance Applicative (Todo a) where pure = Done Todo as <*> Todo bs = Todo $ as ++ bs Todo as <*> _ = Todo as Done f <*> r = fmap f r instance Monad (Todo a) where return = Done Todo as >>= _ = Todo as Done a >>= f = f a It's basically accumulating on the Todos. Either [a] b does not fit because it does not accumulate on the a's. On Tue, Aug 16, 2016 at 11:12 PM, David Kraeutmann wrote:

...

I went from the assumption that he just wants something like

instance Monad (Todo a)

and that implies that b is the type inside of the monad.

On 08/16/2016 08:23 PM, David Kraeutmann wrote:

...
This looks functionally identical to type Todo a b = Either [a] b, and Either has a Monad instance. On 8/16/2016 8:21 PM, Corentin Dupont wrote:

...
Hi guys, is there some library with a Monad (+Applicative, Functor...) instance of the following type:

data Todo a b = Todo [a] | Done b

Thanks! Corentin

_______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

_______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

_______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

Chris Wong

6:59 p.m.

Hi Corentin, That's called the "Validation applicative". I'm on my phone so I can't link, but that phrase should give you a starting point. Note that your type actually has no valid Monad instance that is consistent with the Applicative. That's because while the Applicative accumulates data, the Monad throws it away every time. Chris On Aug 17, 2016 09:56, "Corentin Dupont" wrote:

...

That, right, just to clarify, my instances are like that:

instance Applicative (Todo a) where pure = Done Todo as <*> Todo bs = Todo $ as ++ bs Todo as <*> _ = Todo as Done f <*> r = fmap f r

instance Monad (Todo a) where return = Done Todo as >>= _ = Todo as Done a >>= f = f a

It's basically accumulating on the Todos. Either [a] b does not fit because it does not accumulate on the a's.

On Tue, Aug 16, 2016 at 11:12 PM, David Kraeutmann wrote:

...
I went from the assumption that he just wants something like

instance Monad (Todo a)

and that implies that b is the type inside of the monad.

On 08/16/2016 08:23 PM, David Kraeutmann wrote:

...
This looks functionally identical to type Todo a b = Either [a] b, and Either has a Monad instance. On 8/16/2016 8:21 PM, Corentin Dupont wrote:

...
Hi guys, is there some library with a Monad (+Applicative, Functor...) instance of the following type:

data Todo a b = Todo [a] | Done b

Thanks! Corentin

_______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

_______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

_______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

_______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

David Feuer

7:04 p.m.

Your Monad instance does not correspond to your Applicative instance as required by the class laws. Your Monad instance never appends the way the Applicative one does. And there's no way to make it do so. I don't think you've defined your type the way you really want. But without many details about how you wish to use it, it's hard to say how to fix the problem. On Aug 16, 2016 5:56 PM, "Corentin Dupont" wrote:

...

That, right, just to clarify, my instances are like that:

instance Applicative (Todo a) where pure = Done Todo as <*> Todo bs = Todo $ as ++ bs Todo as <*> _ = Todo as Done f <*> r = fmap f r

instance Monad (Todo a) where return = Done Todo as >>= _ = Todo as Done a >>= f = f a

It's basically accumulating on the Todos. Either [a] b does not fit because it does not accumulate on the a's.

On Tue, Aug 16, 2016 at 11:12 PM, David Kraeutmann wrote:

...
I went from the assumption that he just wants something like

instance Monad (Todo a)

and that implies that b is the type inside of the monad.

On 08/16/2016 08:23 PM, David Kraeutmann wrote:

...
This looks functionally identical to type Todo a b = Either [a] b, and Either has a Monad instance. On 8/16/2016 8:21 PM, Corentin Dupont wrote:

...
Hi guys, is there some library with a Monad (+Applicative, Functor...) instance of the following type:

data Todo a b = Todo [a] | Done b

Thanks! Corentin

_______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

_______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

_______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

_______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

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Chris Wong
Corentin Dupont
David Feuer
David Kraeutmann
eyeinsky .
Francesco Ariis
Jules Mazur
Mihai Maruseac

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