typeclass woes...how to constain a typeclass to be "closed" under an operation....

newer
Significant compilation slowdown...

older
Haskeline and asynchronous messages

Nicholls, Mark

6 Jan 2015 6 Jan '15

12:43 p.m.

This is reposted from the beginnners….I’ve not done Haskell for a while and was struggling to get anything to work, I’ve hopefully refound my feet. Its quite common in maths to have operations in a theory that are (set) closed, i just want to translate that notion to a typeclass I have a suggestion that does work class Foo m where op :: m a -> m (S a) That is closed, but now were working on types of kind • -> • (S can be a type family or a data type…lets say it’s a type family….probably an associated type (if I know what that means)) Is this the idiom/pattern i should follow? Or can the closure contraint be expressed directly in a typeclass any other way? From: Haskell-Cafe [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of Brandon Allbery Sent: 06 January 2015 1:59 PM To: Rob Leslie Cc: Haskell Cafe Subject: Re: [Haskell-cafe] Haskeline and asynchronous messages On Tue, Jan 6, 2015 at 3:27 AM, Rob Leslie mailto:rob@mars.org> wrote: Does anyone have a suggestion on using Haskeline in an environment where another thread may be writing messages to the terminal -- is it possible to somehow print incoming messages above the input line without disturbing the input line? Terminals don't really work that way; you need to be looking at something like curses or vty. -- brandon s allbery kf8nh sine nomine associates allbery.b@gmail.commailto:allbery.b@gmail.com ballbery@sinenomine.netmailto:ballbery@sinenomine.net unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net CONFIDENTIALITY NOTICE This e-mail (and any attached files) is confidential and protected by copyright (and other intellectual property rights). If you are not the intended recipient please e-mail the sender and then delete the email and any attached files immediately. Any further use or dissemination is prohibited. While MTV Networks Europe has taken steps to ensure that this email and any attachments are virus free, it is your responsibility to ensure that this message and any attachments are virus free and do not affect your systems / data. Communicating by email is not 100% secure and carries risks such as delay, data corruption, non-delivery, wrongful interception and unauthorised amendment. If you communicate with us by e-mail, you acknowledge and assume these risks, and you agree to take appropriate measures to minimise these risks when e-mailing us. MTV Networks International, MTV Networks UK & Ireland, Greenhouse, Nickelodeon Viacom Consumer Products, VBSi, Viacom Brand Solutions International, Be Viacom, Viacom International Media Networks and VIMN and Comedy Central are all trading names of MTV Networks Europe. MTV Networks Europe is a partnership between MTV Networks Europe Inc. and Viacom Networks Europe Inc. Address for service in Great Britain is 17-29 Hawley Crescent, London, NW1 8TT.

Attachments:

attachment.html (text/html — 7.7 KB)

Show replies by date

Alexey Shmalko

6 Jan 6 Jan

12:55 p.m.

I'm not sure, but can't closure constraint be expressed as: class Closed m where op :: m -> m Then class Closed is closed under operation op. Seems I'm missing something. Regards, Alexey 2015-01-06 19:43 GMT+02:00 Nicholls, Mark :

...

This is reposted from the beginnners….I’ve not done Haskell for a while and was struggling to get anything to work, I’ve hopefully refound my feet.

Its quite common in maths to have operations in a theory that are (set) closed, i just want to translate that notion to a typeclass

I have a suggestion that does work

class Foo m where

op :: m a -> m (S a)

That is closed, but now were working on types of kind • -> •

(S can be a type family or a data type…lets say it’s a type family….probably an associated type (if I know what that means))

Is this the idiom/pattern i should follow? Or can the closure contraint be expressed directly in a typeclass any other way?

From: Haskell-Cafe [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of Brandon Allbery Sent: 06 January 2015 1:59 PM To: Rob Leslie Cc: Haskell Cafe Subject: Re: [Haskell-cafe] Haskeline and asynchronous messages

On Tue, Jan 6, 2015 at 3:27 AM, Rob Leslie wrote:

Does anyone have a suggestion on using Haskeline in an environment where another thread may be writing messages to the terminal -- is it possible to somehow print incoming messages above the input line without disturbing the input line?

Terminals don't really work that way; you need to be looking at something like curses or vty.

--

brandon s allbery kf8nh sine nomine associates

allbery.b@gmail.com ballbery@sinenomine.net

unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net

CONFIDENTIALITY NOTICE

This e-mail (and any attached files) is confidential and protected by copyright (and other intellectual property rights). If you are not the intended recipient please e-mail the sender and then delete the email and any attached files immediately. Any further use or dissemination is prohibited.

While MTV Networks Europe has taken steps to ensure that this email and any attachments are virus free, it is your responsibility to ensure that this message and any attachments are virus free and do not affect your systems / data.

Communicating by email is not 100% secure and carries risks such as delay, data corruption, non-delivery, wrongful interception and unauthorised amendment. If you communicate with us by e-mail, you acknowledge and assume these risks, and you agree to take appropriate measures to minimise these risks when e-mailing us.

MTV Networks International, MTV Networks UK & Ireland, Greenhouse, Nickelodeon Viacom Consumer Products, VBSi, Viacom Brand Solutions International, Be Viacom, Viacom International Media Networks and VIMN and Comedy Central are all trading names of MTV Networks Europe. MTV Networks Europe is a partnership between MTV Networks Europe Inc. and Viacom Networks Europe Inc. Address for service in Great Britain is 17-29 Hawley Crescent, London, NW1 8TT.

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

Tom Ellis

1:09 p.m.

On Tue, Jan 06, 2015 at 05:43:47PM +0000, Nicholls, Mark wrote:

...

Its quite common in maths to have operations in a theory that are (set) closed, i just want to translate that notion to a typeclass

Do you really need a typeclass (or indeed any way) of doing this? I suspect it will not work. If you consider the multiplication for the monoid of concatenation of lists (++) :: [a] -> [a] -> [a] you see that its type already implies that it is "closed". Tom

Nicholls, Mark

1:53 p.m.

I will post the question again properly tomorrow but your example indeed is almost a good example, but is trivially closed If the operation on monoid was [a]->[b]->[c] That is also closed; ie [c] is also a monoid.... And the typeclass declaration follows the idiom ive suggested This only works for types of kind *->* If i wanted to do this over a type of kind * (ignoring the trivial a->a) Can i express this in a typeclass? Please ignore until i resubmit this question Ps i hate phones Excuse the spelling, sent from a phone with itty bitty keys, it like trying to sow a button on a shirt with a sausage.

...

...
On 6 Jan 2015, at 18:10, Tom Ellis wrote:

On Tue, Jan 06, 2015 at 05:43:47PM +0000, Nicholls, Mark wrote: Its quite common in maths to have operations in a theory that are (set) closed, i just want to translate that notion to a typeclass

Do you really need a typeclass (or indeed any way) of doing this? I suspect it will not work. If you consider the multiplication for the monoid of concatenation of lists

(++) :: [a] -> [a] -> [a]

you see that its type already implies that it is "closed".

Tom _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe CONFIDENTIALITY NOTICE

This e-mail (and any attached files) is confidential and protected by copyright (and other intellectual property rights). If you are not the intended recipient please e-mail the sender and then delete the email and any attached files immediately. Any further use or dissemination is prohibited. While MTV Networks Europe has taken steps to ensure that this email and any attachments are virus free, it is your responsibility to ensure that this message and any attachments are virus free and do not affect your systems / data. Communicating by email is not 100% secure and carries risks such as delay, data corruption, non-delivery, wrongful interception and unauthorised amendment. If you communicate with us by e-mail, you acknowledge and assume these risks, and you agree to take appropriate measures to minimise these risks when e-mailing us. MTV Networks International, MTV Networks UK & Ireland, Greenhouse, Nickelodeon Viacom Consumer Products, VBSi, Viacom Brand Solutions International, Be Viacom, Viacom International Media Networks and VIMN and Comedy Central are all trading names of MTV Networks Europe. MTV Networks Europe is a partnership between MTV Networks Europe Inc. and Viacom Networks Europe Inc. Address for service in Great Britain is 17-29 Hawley Crescent, London, NW1 8TT.

Nicholls, Mark

2:03 p.m.

Bind on monad is a better example, its specified to be closed by the typeclass, but agajn operares on types of kind *->* if i have a function that orbits through multiple types (via type family) of kind * then i have to aggregate them under some wrapper type of kind *->* to define the set closed operation on the wrapper Hmmmmm As you can see i dont do much haskell, and im trying to get my head around how to map simple mathematical concepts into it Excuse the spelling, sent from a phone with itty bitty keys, it like trying to sow a button on a shirt with a sausage.

...

On 6 Jan 2015, at 18:53, Nicholls, Mark wrote:

I will post the question again properly tomorrow but your example indeed is almost a good example, but is trivially closed

If the operation on monoid was

[a]->[b]->[c]

That is also closed; ie [c] is also a monoid.... And the typeclass declaration follows the idiom ive suggested

This only works for types of kind *->*

If i wanted to do this over a type of kind * (ignoring the trivial a->a)

Can i express this in a typeclass?

Please ignore until i resubmit this question

Ps i hate phones

Excuse the spelling, sent from a phone with itty bitty keys, it like trying to sow a button on a shirt with a sausage.

...
...
On 6 Jan 2015, at 18:10, Tom Ellis wrote:

On Tue, Jan 06, 2015 at 05:43:47PM +0000, Nicholls, Mark wrote: Its quite common in maths to have operations in a theory that are (set) closed, i just want to translate that notion to a typeclass

Do you really need a typeclass (or indeed any way) of doing this? I suspect it will not work. If you consider the multiplication for the monoid of concatenation of lists

(++) :: [a] -> [a] -> [a]

you see that its type already implies that it is "closed".

Tom _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe CONFIDENTIALITY NOTICE

adam vogt

2:06 p.m.

Hi, You can constrain the result type to be in the same class by writing something like: {-# LANGUAGE UndecidableInstances, FlexibleInstances #-} {-# LANGUAGE TypeFamilies, FlexibleContexts #-} class Foo_ a -- just to prevent a cycle in superclass constraints instance Foo a => Foo_ a class Foo_ (S a) => Foo a where type S a op :: a -> (S a) -- and an example where you get a compile error if "op x" has an instance, -- but "op (op x)" does not have an instance. instance Foo Int where type S Int = Char op = toEnum instance Foo Char where type S Char = (Char,Char) op x = (x,x) instance Foo (Char,Char) where type S (Char,Char) = Int op (x,y) = fromEnum x On Tue, Jan 6, 2015 at 1:53 PM, Nicholls, Mark wrote:

...

I will post the question again properly tomorrow but your example indeed is almost a good example, but is trivially closed

If the operation on monoid was

[a]->[b]->[c]

That is also closed; ie [c] is also a monoid.... And the typeclass declaration follows the idiom ive suggested

This only works for types of kind *->*

If i wanted to do this over a type of kind * (ignoring the trivial a->a)

Can i express this in a typeclass?

Please ignore until i resubmit this question

Ps i hate phones

Excuse the spelling, sent from a phone with itty bitty keys, it like trying to sow a button on a shirt with a sausage.

...
...
On 6 Jan 2015, at 18:10, Tom Ellis wrote:

On Tue, Jan 06, 2015 at 05:43:47PM +0000, Nicholls, Mark wrote: Its quite common in maths to have operations in a theory that are (set) closed, i just want to translate that notion to a typeclass

Do you really need a typeclass (or indeed any way) of doing this? I suspect it will not work. If you consider the multiplication for the monoid of concatenation of lists

(++) :: [a] -> [a] -> [a]

you see that its type already implies that it is "closed".

Tom _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe CONFIDENTIALITY NOTICE

This e-mail (and any attached files) is confidential and protected by copyright (and other intellectual property rights). If you are not the intended recipient please e-mail the sender and then delete the email and any attached files immediately. Any further use or dissemination is prohibited.

While MTV Networks Europe has taken steps to ensure that this email and any attachments are virus free, it is your responsibility to ensure that this message and any attachments are virus free and do not affect your systems / data.

Communicating by email is not 100% secure and carries risks such as delay, data corruption, non-delivery, wrongful interception and unauthorised amendment. If you communicate with us by e-mail, you acknowledge and assume these risks, and you agree to take appropriate measures to minimise these risks when e-mailing us.

MTV Networks International, MTV Networks UK & Ireland, Greenhouse, Nickelodeon Viacom Consumer Products, VBSi, Viacom Brand Solutions International, Be Viacom, Viacom International Media Networks and VIMN and Comedy Central are all trading names of MTV Networks Europe. MTV Networks Europe is a partnership between MTV Networks Europe Inc. and Viacom Networks Europe Inc. Address for service in Great Britain is 17-29 Hawley Crescent, London, NW1 8TT.

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

Nicholls, Mark

2:14 p.m.

Oooo I'll have a go with this tomorrow Thanks Excuse the spelling, sent from a phone with itty bitty keys, it like trying to sow a button on a shirt with a sausage.

...

On 6 Jan 2015, at 19:06, adam vogt wrote:

Hi,

You can constrain the result type to be in the same class by writing something like:

{-# LANGUAGE UndecidableInstances, FlexibleInstances #-} {-# LANGUAGE TypeFamilies, FlexibleContexts #-}

class Foo_ a -- just to prevent a cycle in superclass constraints instance Foo a => Foo_ a

class Foo_ (S a) => Foo a where type S a op :: a -> (S a)

-- and an example where you get a compile error if "op x" has an instance, -- but "op (op x)" does not have an instance. instance Foo Int where type S Int = Char op = toEnum

instance Foo Char where type S Char = (Char,Char) op x = (x,x)

instance Foo (Char,Char) where type S (Char,Char) = Int op (x,y) = fromEnum x

...
On Tue, Jan 6, 2015 at 1:53 PM, Nicholls, Mark wrote: I will post the question again properly tomorrow but your example indeed is almost a good example, but is trivially closed

If the operation on monoid was

[a]->[b]->[c]

That is also closed; ie [c] is also a monoid.... And the typeclass declaration follows the idiom ive suggested

This only works for types of kind *->*

If i wanted to do this over a type of kind * (ignoring the trivial a->a)

Can i express this in a typeclass?

Please ignore until i resubmit this question

Ps i hate phones

Excuse the spelling, sent from a phone with itty bitty keys, it like trying to sow a button on a shirt with a sausage.

...
...
On 6 Jan 2015, at 18:10, Tom Ellis wrote:

On Tue, Jan 06, 2015 at 05:43:47PM +0000, Nicholls, Mark wrote: Its quite common in maths to have operations in a theory that are (set) closed, i just want to translate that notion to a typeclass

Do you really need a typeclass (or indeed any way) of doing this? I suspect it will not work. If you consider the multiplication for the monoid of concatenation of lists

(++) :: [a] -> [a] -> [a]

you see that its type already implies that it is "closed".

Tom _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe CONFIDENTIALITY NOTICE

This e-mail (and any attached files) is confidential and protected by copyright (and other intellectual property rights). If you are not the intended recipient please e-mail the sender and then delete the email and any attached files immediately. Any further use or dissemination is prohibited.

While MTV Networks Europe has taken steps to ensure that this email and any attachments are virus free, it is your responsibility to ensure that this message and any attachments are virus free and do not affect your systems / data.

Communicating by email is not 100% secure and carries risks such as delay, data corruption, non-delivery, wrongful interception and unauthorised amendment. If you communicate with us by e-mail, you acknowledge and assume these risks, and you agree to take appropriate measures to minimise these risks when e-mailing us.

MTV Networks International, MTV Networks UK & Ireland, Greenhouse, Nickelodeon Viacom Consumer Products, VBSi, Viacom Brand Solutions International, Be Viacom, Viacom International Media Networks and VIMN and Comedy Central are all trading names of MTV Networks Europe. MTV Networks Europe is a partnership between MTV Networks Europe Inc. and Viacom Networks Europe Inc. Address for service in Great Britain is 17-29 Hawley Crescent, London, NW1 8TT.

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe CONFIDENTIALITY NOTICE

Nicholls, Mark

2:18 p.m.

In fact i had tried somethjng very much like this but without the Foo_ and haskell wasnt happy with the cyclic definition So maybe this is the answer! I'll let you know Excuse the spelling, sent from a phone with itty bitty keys, it like trying to sow a button on a shirt with a sausage.

...

On 6 Jan 2015, at 19:14, Nicholls, Mark wrote:

Oooo

I'll have a go with this tomorrow

Thanks

Excuse the spelling, sent from a phone with itty bitty keys, it like trying to sow a button on a shirt with a sausage.

...
On 6 Jan 2015, at 19:06, adam vogt wrote:

Hi,

You can constrain the result type to be in the same class by writing something like:

{-# LANGUAGE UndecidableInstances, FlexibleInstances #-} {-# LANGUAGE TypeFamilies, FlexibleContexts #-}

class Foo_ a -- just to prevent a cycle in superclass constraints instance Foo a => Foo_ a

class Foo_ (S a) => Foo a where type S a op :: a -> (S a)

-- and an example where you get a compile error if "op x" has an instance, -- but "op (op x)" does not have an instance. instance Foo Int where type S Int = Char op = toEnum

instance Foo Char where type S Char = (Char,Char) op x = (x,x)

instance Foo (Char,Char) where type S (Char,Char) = Int op (x,y) = fromEnum x

...
On Tue, Jan 6, 2015 at 1:53 PM, Nicholls, Mark wrote: I will post the question again properly tomorrow but your example indeed is almost a good example, but is trivially closed

If the operation on monoid was

[a]->[b]->[c]

That is also closed; ie [c] is also a monoid.... And the typeclass declaration follows the idiom ive suggested

This only works for types of kind *->*

If i wanted to do this over a type of kind * (ignoring the trivial a->a)

Can i express this in a typeclass?

Please ignore until i resubmit this question

Ps i hate phones

Excuse the spelling, sent from a phone with itty bitty keys, it like trying to sow a button on a shirt with a sausage.

...
...
On 6 Jan 2015, at 18:10, Tom Ellis wrote:

On Tue, Jan 06, 2015 at 05:43:47PM +0000, Nicholls, Mark wrote: Its quite common in maths to have operations in a theory that are (set) closed, i just want to translate that notion to a typeclass

Do you really need a typeclass (or indeed any way) of doing this? I suspect it will not work. If you consider the multiplication for the monoid of concatenation of lists

(++) :: [a] -> [a] -> [a]

you see that its type already implies that it is "closed".

Tom _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe CONFIDENTIALITY NOTICE

This e-mail (and any attached files) is confidential and protected by copyright (and other intellectual property rights). If you are not the intended recipient please e-mail the sender and then delete the email and any attached files immediately. Any further use or dissemination is prohibited.

While MTV Networks Europe has taken steps to ensure that this email and any attachments are virus free, it is your responsibility to ensure that this message and any attachments are virus free and do not affect your systems / data.

Communicating by email is not 100% secure and carries risks such as delay, data corruption, non-delivery, wrongful interception and unauthorised amendment. If you communicate with us by e-mail, you acknowledge and assume these risks, and you agree to take appropriate measures to minimise these risks when e-mailing us.

MTV Networks International, MTV Networks UK & Ireland, Greenhouse, Nickelodeon Viacom Consumer Products, VBSi, Viacom Brand Solutions International, Be Viacom, Viacom International Media Networks and VIMN and Comedy Central are all trading names of MTV Networks Europe. MTV Networks Europe is a partnership between MTV Networks Europe Inc. and Viacom Networks Europe Inc. Address for service in Great Britain is 17-29 Hawley Crescent, London, NW1 8TT.

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe CONFIDENTIALITY NOTICE

3788

Age (days ago)

3788

Last active (days ago)

List overview

Download

7 comments

4 participants

participants (4)

adam vogt
Alexey Shmalko
Nicholls, Mark
Tom Ellis