- ghc-devs - Haskell.org

setsockopt IPV2_TCLASS 8
by Simon Peyton Jones 03 Jun '19

03 Jun '19

I'm getting a lot of these messages from ssh when using git setsockopt IPV6_TCLASS 8: Operation not permitted: (Same thing when directly invoking ssh git(a)gitlab.haskell.org<mailto:git@gitlab.haskell.org>) Should I worry? Simon

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Pushing to gitlab.haskell.org
by Simon Peyton Jones 03 Jun '19

03 Jun '19

Devs Suddenly I can't push to (a non-master branch on) gitlab.haskell.org. In .git/config I have [remote "origin"] url = https://gitlab.haskell.org/ghc/ghc fetch = +refs/heads/*:refs/remotes/origin/* [branch "master"] remote = origin merge = refs/heads/master An attempt to push leads to a request for a username. If I enter one, a request for a password. simonpj@MSRC-3645512:~/code/HEAD$ git push origin wip/T16735 Username for 'https://gitlab.haskell.org': C-c C-c I thought I had SSH keys uploaded. But in fact I found that my id_rsa.pub was a bit different to the one in gitlab. Not sure _how_ that happened, or why it hasn't bitten before. So I uploaded a new id_rsa.pub key. Same behaviour. So I tried ssh -v gitlab.haskell.org, and got the output below. It seems to skip id_dsa, but doesn't even try id_rsa. Can anyone help? This is tiresome. Thanks Simon simonpj@MSRC-3645512:~/code/HEAD$ ssh -v gitlab.haskell.org OpenSSH_7.6p1 Ubuntu-4, OpenSSL 1.0.2n 7 Dec 2017 debug1: Reading configuration data /home/simonpj/.ssh/config debug1: Reading configuration data /etc/ssh/ssh_config debug1: /etc/ssh/ssh_config line 19: Applying options for * debug1: Connecting to gitlab.haskell.org [2604:1380:0:8900::3] port 22. debug1: Connection established. debug1: identity file /home/simonpj/.ssh/id_rsa type 0 debug1: key_load_public: No such file or directory debug1: identity file /home/simonpj/.ssh/id_rsa-cert type -1 debug1: identity file /home/simonpj/.ssh/id_dsa type 1 debug1: key_load_public: No such file or directory debug1: identity file /home/simonpj/.ssh/id_dsa-cert type -1 debug1: key_load_public: No such file or directory debug1: identity file /home/simonpj/.ssh/id_ecdsa type -1 debug1: key_load_public: No such file or directory debug1: identity file /home/simonpj/.ssh/id_ecdsa-cert type -1 debug1: key_load_public: No such file or directory debug1: identity file /home/simonpj/.ssh/id_ed25519 type -1 debug1: key_load_public: No such file or directory debug1: identity file /home/simonpj/.ssh/id_ed25519-cert type -1 debug1: Local version string SSH-2.0-OpenSSH_7.6p1 Ubuntu-4 debug1: Remote protocol version 2.0, remote software version OpenSSH_7.9 debug1: match: OpenSSH_7.9 pat OpenSSH* compat 0x04000000 debug1: Authenticating to gitlab.haskell.org:22 as 'simonpj' debug1: SSH2_MSG_KEXINIT sent debug1: SSH2_MSG_KEXINIT received debug1: kex: algorithm: curve25519-sha256(a)libssh.org debug1: kex: host key algorithm: ssh-ed25519 debug1: kex: server->client cipher: chacha20-poly1305(a)openssh.com MAC: <implicit> compression: none debug1: kex: client->server cipher: chacha20-poly1305(a)openssh.com MAC: <implicit> compression: none debug1: expecting SSH2_MSG_KEX_ECDH_REPLY debug1: Server host key: ssh-ed25519 SHA256:wtE9yoEHLsotzqKfbDs1JIqR+c8ZZyW+FAJAmteBfcI debug1: Host 'gitlab.haskell.org' is known and matches the ED25519 host key. debug1: Found key in /home/simonpj/.ssh/known_hosts:7 debug1: rekey after 134217728 blocks debug1: SSH2_MSG_NEWKEYS sent debug1: expecting SSH2_MSG_NEWKEYS debug1: SSH2_MSG_NEWKEYS received debug1: rekey after 134217728 blocks debug1: Skipping ssh-dss key /home/simonpj/.ssh/id_dsa - not in PubkeyAcceptedKeyTypes debug1: SSH2_MSG_EXT_INFO received debug1: kex_input_ext_info: server-sig-algs=<ssh-ed25519,ssh-rsa,rsa-sha2-256,rsa-sha2-512,ssh-dss,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521> debug1: SSH2_MSG_SERVICE_ACCEPT received debug1: Authentications that can continue: publickey,password,keyboard-interactive debug1: Next authentication method: publickey debug1: Offering public key: RSA SHA256:H1l824hIxHozwRuEqdaYJjW10mRRlQVUhxREvuseqtU /home/simonpj/.ssh/id_rsa debug1: Authentications that can continue: publickey,password,keyboard-interactive debug1: Trying private key: /home/simonpj/.ssh/id_ecdsa debug1: Trying private key: /home/simonpj/.ssh/id_ed25519 debug1: Next authentication method: keyboard-interactive Password: C-c C-c simonpj@MSRC-3645512:~/code/HEAD$

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Cmm syntax page on wiki
by Takenobu Tani 01 Jun '19

01 Jun '19

Hi devs, I wrote a wiki page for Cmm syntax [1] to improve readability for ghc developers. Could you tell me if there are any problems or errors? I'll update them or remove the page. [1]: https://gitlab.haskell.org/ghc/ghc/wikis/commentary/compiler/cmm-syntax Regards, Takenobu

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search on GItlab
by Simon Peyton Jones 31 May '19

31 May '19

If I search in GitLab for "checkExpectedKind" I don't fine #16635, which clearly mentions that. Why not? Thanks Simon

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RE: Container type classes
by Andrey Mokhov 31 May '19

31 May '19

Thanks again Iavor, Despite the type inference issue, and the fact that this requires a separate type class, this is the best solution I've seen so far. Cheers, Andrey -----Original Message----- From: Iavor Diatchki [mailto:iavor.diatchki@gmail.com] Sent: 30 May 2019 23:16 To: Andrey Mokhov <andrey.mokhov(a)newcastle.ac.uk> Cc: Brandon Allbery <allbery.b(a)gmail.com>; Andreas Klebinger <klebinger.andreas(a)gmx.at>; ghc-devs(a)haskell.org Subject: Re: Container type classes Yeah, there is really no relation between the two parameters of `Fun`, so you'd have to specify the intermediate type manually. For example: add3 :: forall s. (Fun s s, Elem s ~ Int) => s -> s add3 = colMap @s (+1) . colMap (+2) I wouldn't say that it's a particularly convenient interface to work with, unless you are working in a setting where most of the containers have known types. On Thu, May 30, 2019 at 2:58 PM Andrey Mokhov <andrey.mokhov(a)newcastle.ac.uk> wrote: > > Many thanks Iavor, > > This looks very promising! I played with your encoding a little, but quickly came across type inference issues. The following doesn't compile: > > add3 :: (Fun s s, Elem s ~ Int) => s -> s > add3 = colMap (+1) . colMap (+2) > > I'm getting: > > * Could not deduce: Elem a0 ~ Int > from the context: (Fun s s, Elem s ~ Int) > bound by the type signature for: > add3 :: forall s. (Fun s s, Elem s ~ Int) => s -> s > Expected type: Elem a0 -> Elem s > Actual type: Int -> Int > The type variable `a0' is ambiguous > > Fun s s is supposed to say that the intermediate type is `s` too, but I guess this is not how type class resolution works. > > Cheers, > Andrey > > -----Original Message----- > From: Iavor Diatchki [mailto:iavor.diatchki@gmail.com] > Sent: 30 May 2019 22:38 > To: Brandon Allbery <allbery.b(a)gmail.com> > Cc: Andrey Mokhov <andrey.mokhov(a)newcastle.ac.uk>; Andreas Klebinger <klebinger.andreas(a)gmx.at>; ghc-devs(a)haskell.org > Subject: Re: Container type classes > > This is how you could define `map`. This is just for fun, and to > discuss Haskell idioms---I am not suggesting we should do it. Of > course, it might be a bit more general than what you'd like---for > example it allows defining instances like `Fun IntSet (Set Int)` that, > perhaps?, you'd like to disallow: > > {-# LANGUAGE MultiParamTypeClasses, TypeFamilies #-} > > import Data.Set (Set) > import qualified Data.Set as Set > import Data.IntSet (IntSet) > import qualified Data.IntSet as ISet > > class Col t where > type Elem t > -- ... As in Andreas's example > > class (Col a, Col b) => Fun a b where > colMap :: (Elem a -> Elem b) -> a -> b > > instance Col (Set a) where > type Elem (Set a) = a > > instance Col IntSet where > type Elem IntSet = Int > > instance Fun IntSet IntSet where > colMap = ISet.map > > instance Ord b => Fun (Set a) (Set b) where > colMap = Set.map > > On Thu, May 30, 2019 at 2:32 PM Brandon Allbery <allbery.b(a)gmail.com> wrote: > > > > They can, with more work. You want indexed monads, so you can describe types that have e.g. an ordering constraint as well as the Monad constraint. > > > > On Thu, May 30, 2019 at 5:26 PM Andrey Mokhov <andrey.mokhov(a)newcastle.ac.uk> wrote: > >> > >> Hi Artem, > >> > >> > >> > >> Thanks for the pointer, but this doesn’t seem to be a solution to my challenge: they simply give up on overloading `map` for both Set and IntSet. As a result, we can’t write polymorphic functions over Set and IntSet if they involve any mapping. > >> > >> > >> > >> I looked at the prototype by Andreas Klebinger, and it doesn’t include the method `setMap` either. > >> > >> > >> > >> Perhaps, Haskell’s type classes just can’t cope with this problem. > >> > >> > >> > >> *ducks for cover* > >> > >> > >> > >> Cheers, > >> > >> Andrey > >> > >> > >> > >> From: Artem Pelenitsyn [mailto:a.pelenitsyn@gmail.com] > >> Sent: 30 May 2019 20:56 > >> To: Andrey Mokhov <andrey.mokhov(a)newcastle.ac.uk> > >> Cc: ghc-devs(a)haskell.org; Andreas Klebinger <klebinger.andreas(a)gmx.at> > >> Subject: Re: Container type classes > >> > >> > >> > >> Hi Andrey, > >> > >> > >> > >> FWIW, mono-traversable (http://hackage.haskell.org/package/mono-traversable) suggests decoupling IsSet and Funtor-like. > >> > >> > >> > >> In a nutshell, they define the IsSet class (in Data.Containers) with typical set operations like member and singleton, union and intersection. And then they tackle a (seemingly) independent problem of mapping monomorphic containers (like IntSet, ByteString, etc.) with a separate class MonoFunctor (in Data.MonoTraversable): > >> > >> > >> > >> class MonoFunctor mono where > >> omap :: (Element mono -> Element mono) -> mono -> mono > >> > >> > >> > >> And gazillion of instances for both polymorphic containers with a fixed type parameter and monomorphic ones. > >> > >> > >> > >> -- > >> > >> Best wishes, > >> > >> Artem > >> > >> > >> > >> On Thu, 30 May 2019 at 20:11, Andrey Mokhov <andrey.mokhov(a)newcastle.ac.uk> wrote: > >> > >> Hi all, > >> > >> I tried to use type classes for unifying APIs of several similar data structures and it didn't work well. (In my case I was working with graphs, instead of sets or maps.) > >> > >> First, you rarely want to be polymorphic over the set representation, because you care about performance. You really want to use that Very.Special.Set.insert because it has the right performance characteristics for your task at hand. I found only *one* use-case for writing polymorphic functions operating on something like IsSet: the testsuite. Of course, it is very nice to write a single property test like > >> > >> memberInsertProperty x set = (member x (insert x set) == True) > >> > >> and then use it for testing all set data structures that implement `member` and `insert`. Here you don't care about performance, only about correctness! > >> > >> However, this approach leads to problems with type inference, confusing error messages, and complexity. I found that it is much nicer to use explicit dictionary passing and write something like this instead: > >> > >> memberInsertProperty SetAPI{..} x set = (member x (insert x set) == True) > >> > >> where `member` and `insert` come from the SetAPI record via RecordWildCards. > >> > >> Finally, I'm not even sure how to create a type class covering Set and IntSet with the following two methods: > >> > >> singleton :: a -> Set a > >> map :: Ord b => (a -> b) -> Set a -> Set b > >> > >> singleton :: Int -> IntSet > >> map :: (Int -> Int) -> IntSet -> IntSet > >> > >> Could anyone please enlighten me about the right way to abstract over this using type classes? > >> > >> I tried a few approaches, for example: > >> > >> class IsSet s where > >> type Elem s > >> singleton :: Elem s -> s > >> map :: Ord (Elem t) => (Elem s -> Elem t) -> s -> t > >> > >> Looks nice, but I can't define the IntSet instance: > >> > >> instance IsSet IntSet where > >> type Elem IntSet = Int > >> singleton = IntSet.singleton > >> map = IntSet.map > >> > >> This fails with: Couldn't match type `t' with `IntSet' -- and indeed, how do I tell the compiler that in the IntSet case s ~ t in the map signature? Shall I add more associated types, or "associated constraints" using ConstraintKinds? I tried and failed, at various stages, repeatedly. > >> > >> ...And then you discover that there is Set.cartesianProduct :: Set a -> Set b -> Set (a, b), but no equivalent in IntSet and things get even more grim. > >> > >> Cheers, > >> Andrey > >> > >> _______________________________________________ > >> ghc-devs mailing list > >> ghc-devs(a)haskell.org > >> http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs > >> > >> _______________________________________________ > >> ghc-devs mailing list > >> ghc-devs(a)haskell.org > >> http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs > > > > > > > > -- > > brandon s allbery kf8nh > > allbery.b(a)gmail.com > > _______________________________________________ > > ghc-devs mailing list > > ghc-devs(a)haskell.org > > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs

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RE: Container type classes
by Andrey Mokhov 30 May '19

30 May '19

Many thanks Iavor, This looks very promising! I played with your encoding a little, but quickly came across type inference issues. The following doesn't compile: add3 :: (Fun s s, Elem s ~ Int) => s -> s add3 = colMap (+1) . colMap (+2) I'm getting: * Could not deduce: Elem a0 ~ Int from the context: (Fun s s, Elem s ~ Int) bound by the type signature for: add3 :: forall s. (Fun s s, Elem s ~ Int) => s -> s Expected type: Elem a0 -> Elem s Actual type: Int -> Int The type variable `a0' is ambiguous Fun s s is supposed to say that the intermediate type is `s` too, but I guess this is not how type class resolution works. Cheers, Andrey -----Original Message----- From: Iavor Diatchki [mailto:iavor.diatchki@gmail.com] Sent: 30 May 2019 22:38 To: Brandon Allbery <allbery.b(a)gmail.com> Cc: Andrey Mokhov <andrey.mokhov(a)newcastle.ac.uk>; Andreas Klebinger <klebinger.andreas(a)gmx.at>; ghc-devs(a)haskell.org Subject: Re: Container type classes This is how you could define `map`. This is just for fun, and to discuss Haskell idioms---I am not suggesting we should do it. Of course, it might be a bit more general than what you'd like---for example it allows defining instances like `Fun IntSet (Set Int)` that, perhaps?, you'd like to disallow: {-# LANGUAGE MultiParamTypeClasses, TypeFamilies #-} import Data.Set (Set) import qualified Data.Set as Set import Data.IntSet (IntSet) import qualified Data.IntSet as ISet class Col t where type Elem t -- ... As in Andreas's example class (Col a, Col b) => Fun a b where colMap :: (Elem a -> Elem b) -> a -> b instance Col (Set a) where type Elem (Set a) = a instance Col IntSet where type Elem IntSet = Int instance Fun IntSet IntSet where colMap = ISet.map instance Ord b => Fun (Set a) (Set b) where colMap = Set.map On Thu, May 30, 2019 at 2:32 PM Brandon Allbery <allbery.b(a)gmail.com> wrote: > > They can, with more work. You want indexed monads, so you can describe types that have e.g. an ordering constraint as well as the Monad constraint. > > On Thu, May 30, 2019 at 5:26 PM Andrey Mokhov <andrey.mokhov(a)newcastle.ac.uk> wrote: >> >> Hi Artem, >> >> >> >> Thanks for the pointer, but this doesn’t seem to be a solution to my challenge: they simply give up on overloading `map` for both Set and IntSet. As a result, we can’t write polymorphic functions over Set and IntSet if they involve any mapping. >> >> >> >> I looked at the prototype by Andreas Klebinger, and it doesn’t include the method `setMap` either. >> >> >> >> Perhaps, Haskell’s type classes just can’t cope with this problem. >> >> >> >> *ducks for cover* >> >> >> >> Cheers, >> >> Andrey >> >> >> >> From: Artem Pelenitsyn [mailto:a.pelenitsyn@gmail.com] >> Sent: 30 May 2019 20:56 >> To: Andrey Mokhov <andrey.mokhov(a)newcastle.ac.uk> >> Cc: ghc-devs(a)haskell.org; Andreas Klebinger <klebinger.andreas(a)gmx.at> >> Subject: Re: Container type classes >> >> >> >> Hi Andrey, >> >> >> >> FWIW, mono-traversable (http://hackage.haskell.org/package/mono-traversable) suggests decoupling IsSet and Funtor-like. >> >> >> >> In a nutshell, they define the IsSet class (in Data.Containers) with typical set operations like member and singleton, union and intersection. And then they tackle a (seemingly) independent problem of mapping monomorphic containers (like IntSet, ByteString, etc.) with a separate class MonoFunctor (in Data.MonoTraversable): >> >> >> >> class MonoFunctor mono where >> omap :: (Element mono -> Element mono) -> mono -> mono >> >> >> >> And gazillion of instances for both polymorphic containers with a fixed type parameter and monomorphic ones. >> >> >> >> -- >> >> Best wishes, >> >> Artem >> >> >> >> On Thu, 30 May 2019 at 20:11, Andrey Mokhov <andrey.mokhov(a)newcastle.ac.uk> wrote: >> >> Hi all, >> >> I tried to use type classes for unifying APIs of several similar data structures and it didn't work well. (In my case I was working with graphs, instead of sets or maps.) >> >> First, you rarely want to be polymorphic over the set representation, because you care about performance. You really want to use that Very.Special.Set.insert because it has the right performance characteristics for your task at hand. I found only *one* use-case for writing polymorphic functions operating on something like IsSet: the testsuite. Of course, it is very nice to write a single property test like >> >> memberInsertProperty x set = (member x (insert x set) == True) >> >> and then use it for testing all set data structures that implement `member` and `insert`. Here you don't care about performance, only about correctness! >> >> However, this approach leads to problems with type inference, confusing error messages, and complexity. I found that it is much nicer to use explicit dictionary passing and write something like this instead: >> >> memberInsertProperty SetAPI{..} x set = (member x (insert x set) == True) >> >> where `member` and `insert` come from the SetAPI record via RecordWildCards. >> >> Finally, I'm not even sure how to create a type class covering Set and IntSet with the following two methods: >> >> singleton :: a -> Set a >> map :: Ord b => (a -> b) -> Set a -> Set b >> >> singleton :: Int -> IntSet >> map :: (Int -> Int) -> IntSet -> IntSet >> >> Could anyone please enlighten me about the right way to abstract over this using type classes? >> >> I tried a few approaches, for example: >> >> class IsSet s where >> type Elem s >> singleton :: Elem s -> s >> map :: Ord (Elem t) => (Elem s -> Elem t) -> s -> t >> >> Looks nice, but I can't define the IntSet instance: >> >> instance IsSet IntSet where >> type Elem IntSet = Int >> singleton = IntSet.singleton >> map = IntSet.map >> >> This fails with: Couldn't match type `t' with `IntSet' -- and indeed, how do I tell the compiler that in the IntSet case s ~ t in the map signature? Shall I add more associated types, or "associated constraints" using ConstraintKinds? I tried and failed, at various stages, repeatedly. >> >> ...And then you discover that there is Set.cartesianProduct :: Set a -> Set b -> Set (a, b), but no equivalent in IntSet and things get even more grim. >> >> Cheers, >> Andrey >> >> _______________________________________________ >> ghc-devs mailing list >> ghc-devs(a)haskell.org >> http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs >> >> _______________________________________________ >> ghc-devs mailing list >> ghc-devs(a)haskell.org >> http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs > > > > -- > brandon s allbery kf8nh > allbery.b(a)gmail.com > _______________________________________________ > ghc-devs mailing list > ghc-devs(a)haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs

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RE: Container type classes
by Andrey Mokhov 30 May '19

30 May '19

Hi Brandon, Could you show the code? I have no idea how indexed monads could possibly be related here. All I want is to have a type class that unifies these two methods: singleton :: a -> Set a map :: Ord b => (a -> b) -> Set a -> Set b singleton :: Int -> IntSet map :: (Int -> Int) -> IntSet -> IntSet Cheers, Andrey From: Brandon Allbery [mailto:allbery.b@gmail.com] Sent: 30 May 2019 22:32 To: Andrey Mokhov <andrey.mokhov(a)newcastle.ac.uk> Cc: Artem Pelenitsyn <a.pelenitsyn(a)gmail.com>; Andreas Klebinger <klebinger.andreas(a)gmx.at>; ghc-devs(a)haskell.org Subject: Re: Container type classes They can, with more work. You want indexed monads, so you can describe types that have e.g. an ordering constraint as well as the Monad constraint. On Thu, May 30, 2019 at 5:26 PM Andrey Mokhov <andrey.mokhov(a)newcastle.ac.uk<mailto:andrey.mokhov@newcastle.ac.uk>> wrote: Hi Artem, Thanks for the pointer, but this doesn’t seem to be a solution to my challenge: they simply give up on overloading `map` for both Set and IntSet. As a result, we can’t write polymorphic functions over Set and IntSet if they involve any mapping. I looked at the prototype by Andreas Klebinger, and it doesn’t include the method `setMap` either. Perhaps, Haskell’s type classes just can’t cope with this problem. *ducks for cover* Cheers, Andrey From: Artem Pelenitsyn [mailto:a.pelenitsyn@gmail.com<mailto:a.pelenitsyn@gmail.com>] Sent: 30 May 2019 20:56 To: Andrey Mokhov <andrey.mokhov(a)newcastle.ac.uk<mailto:andrey.mokhov@newcastle.ac.uk>> Cc: ghc-devs(a)haskell.org<mailto:ghc-devs@haskell.org>; Andreas Klebinger <klebinger.andreas(a)gmx.at<mailto:klebinger.andreas@gmx.at>> Subject: Re: Container type classes Hi Andrey, FWIW, mono-traversable (http://hackage.haskell.org/package/mono-traversable) suggests decoupling IsSet and Funtor-like. In a nutshell, they define the IsSet class (in Data.Containers) with typical set operations like member and singleton, union and intersection. And then they tackle a (seemingly) independent problem of mapping monomorphic containers (like IntSet, ByteString, etc.) with a separate class MonoFunctor (in Data.MonoTraversable): class MonoFunctor mono where omap :: (Element mono -> Element mono) -> mono -> mono And gazillion of instances for both polymorphic containers with a fixed type parameter and monomorphic ones. -- Best wishes, Artem On Thu, 30 May 2019 at 20:11, Andrey Mokhov <andrey.mokhov(a)newcastle.ac.uk<mailto:andrey.mokhov@newcastle.ac.uk>> wrote: Hi all, I tried to use type classes for unifying APIs of several similar data structures and it didn't work well. (In my case I was working with graphs, instead of sets or maps.) First, you rarely want to be polymorphic over the set representation, because you care about performance. You really want to use that Very.Special.Set.insert because it has the right performance characteristics for your task at hand. I found only *one* use-case for writing polymorphic functions operating on something like IsSet: the testsuite. Of course, it is very nice to write a single property test like memberInsertProperty x set = (member x (insert x set) == True) and then use it for testing all set data structures that implement `member` and `insert`. Here you don't care about performance, only about correctness! However, this approach leads to problems with type inference, confusing error messages, and complexity. I found that it is much nicer to use explicit dictionary passing and write something like this instead: memberInsertProperty SetAPI{..} x set = (member x (insert x set) == True) where `member` and `insert` come from the SetAPI record via RecordWildCards. Finally, I'm not even sure how to create a type class covering Set and IntSet with the following two methods: singleton :: a -> Set a map :: Ord b => (a -> b) -> Set a -> Set b singleton :: Int -> IntSet map :: (Int -> Int) -> IntSet -> IntSet Could anyone please enlighten me about the right way to abstract over this using type classes? I tried a few approaches, for example: class IsSet s where type Elem s singleton :: Elem s -> s map :: Ord (Elem t) => (Elem s -> Elem t) -> s -> t Looks nice, but I can't define the IntSet instance: instance IsSet IntSet where type Elem IntSet = Int singleton = IntSet.singleton map = IntSet.map This fails with: Couldn't match type `t' with `IntSet' -- and indeed, how do I tell the compiler that in the IntSet case s ~ t in the map signature? Shall I add more associated types, or "associated constraints" using ConstraintKinds? I tried and failed, at various stages, repeatedly. ...And then you discover that there is Set.cartesianProduct :: Set a -> Set b -> Set (a, b), but no equivalent in IntSet and things get even more grim. Cheers, Andrey _______________________________________________ ghc-devs mailing list ghc-devs(a)haskell.org<mailto:ghc-devs@haskell.org> http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs _______________________________________________ ghc-devs mailing list ghc-devs(a)haskell.org<mailto:ghc-devs@haskell.org> http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs -- brandon s allbery kf8nh allbery.b(a)gmail.com<mailto:allbery.b@gmail.com>

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RE: Container type classes
by Andrey Mokhov 30 May '19

30 May '19

Hi Artem, Thanks for the pointer, but this doesn’t seem to be a solution to my challenge: they simply give up on overloading `map` for both Set and IntSet. As a result, we can’t write polymorphic functions over Set and IntSet if they involve any mapping. I looked at the prototype by Andreas Klebinger, and it doesn’t include the method `setMap` either. Perhaps, Haskell’s type classes just can’t cope with this problem. *ducks for cover* Cheers, Andrey From: Artem Pelenitsyn [mailto:a.pelenitsyn@gmail.com] Sent: 30 May 2019 20:56 To: Andrey Mokhov <andrey.mokhov(a)newcastle.ac.uk> Cc: ghc-devs(a)haskell.org; Andreas Klebinger <klebinger.andreas(a)gmx.at> Subject: Re: Container type classes Hi Andrey, FWIW, mono-traversable (http://hackage.haskell.org/package/mono-traversable) suggests decoupling IsSet and Funtor-like. In a nutshell, they define the IsSet class (in Data.Containers) with typical set operations like member and singleton, union and intersection. And then they tackle a (seemingly) independent problem of mapping monomorphic containers (like IntSet, ByteString, etc.) with a separate class MonoFunctor (in Data.MonoTraversable): class MonoFunctor mono where omap :: (Element mono -> Element mono) -> mono -> mono And gazillion of instances for both polymorphic containers with a fixed type parameter and monomorphic ones. -- Best wishes, Artem On Thu, 30 May 2019 at 20:11, Andrey Mokhov <andrey.mokhov(a)newcastle.ac.uk<mailto:andrey.mokhov@newcastle.ac.uk>> wrote: Hi all, I tried to use type classes for unifying APIs of several similar data structures and it didn't work well. (In my case I was working with graphs, instead of sets or maps.) First, you rarely want to be polymorphic over the set representation, because you care about performance. You really want to use that Very.Special.Set.insert because it has the right performance characteristics for your task at hand. I found only *one* use-case for writing polymorphic functions operating on something like IsSet: the testsuite. Of course, it is very nice to write a single property test like memberInsertProperty x set = (member x (insert x set) == True) and then use it for testing all set data structures that implement `member` and `insert`. Here you don't care about performance, only about correctness! However, this approach leads to problems with type inference, confusing error messages, and complexity. I found that it is much nicer to use explicit dictionary passing and write something like this instead: memberInsertProperty SetAPI{..} x set = (member x (insert x set) == True) where `member` and `insert` come from the SetAPI record via RecordWildCards. Finally, I'm not even sure how to create a type class covering Set and IntSet with the following two methods: singleton :: a -> Set a map :: Ord b => (a -> b) -> Set a -> Set b singleton :: Int -> IntSet map :: (Int -> Int) -> IntSet -> IntSet Could anyone please enlighten me about the right way to abstract over this using type classes? I tried a few approaches, for example: class IsSet s where type Elem s singleton :: Elem s -> s map :: Ord (Elem t) => (Elem s -> Elem t) -> s -> t Looks nice, but I can't define the IntSet instance: instance IsSet IntSet where type Elem IntSet = Int singleton = IntSet.singleton map = IntSet.map This fails with: Couldn't match type `t' with `IntSet' -- and indeed, how do I tell the compiler that in the IntSet case s ~ t in the map signature? Shall I add more associated types, or "associated constraints" using ConstraintKinds? I tried and failed, at various stages, repeatedly. ...And then you discover that there is Set.cartesianProduct :: Set a -> Set b -> Set (a, b), but no equivalent in IntSet and things get even more grim. Cheers, Andrey _______________________________________________ ghc-devs mailing list ghc-devs(a)haskell.org<mailto:ghc-devs@haskell.org> http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs

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RE: Container type classes
by Andrey Mokhov 30 May '19

30 May '19

Hi all, I tried to use type classes for unifying APIs of several similar data structures and it didn't work well. (In my case I was working with graphs, instead of sets or maps.) First, you rarely want to be polymorphic over the set representation, because you care about performance. You really want to use that Very.Special.Set.insert because it has the right performance characteristics for your task at hand. I found only *one* use-case for writing polymorphic functions operating on something like IsSet: the testsuite. Of course, it is very nice to write a single property test like memberInsertProperty x set = (member x (insert x set) == True) and then use it for testing all set data structures that implement `member` and `insert`. Here you don't care about performance, only about correctness! However, this approach leads to problems with type inference, confusing error messages, and complexity. I found that it is much nicer to use explicit dictionary passing and write something like this instead: memberInsertProperty SetAPI{..} x set = (member x (insert x set) == True) where `member` and `insert` come from the SetAPI record via RecordWildCards. Finally, I'm not even sure how to create a type class covering Set and IntSet with the following two methods: singleton :: a -> Set a map :: Ord b => (a -> b) -> Set a -> Set b singleton :: Int -> IntSet map :: (Int -> Int) -> IntSet -> IntSet Could anyone please enlighten me about the right way to abstract over this using type classes? I tried a few approaches, for example: class IsSet s where type Elem s singleton :: Elem s -> s map :: Ord (Elem t) => (Elem s -> Elem t) -> s -> t Looks nice, but I can't define the IntSet instance: instance IsSet IntSet where type Elem IntSet = Int singleton = IntSet.singleton map = IntSet.map This fails with: Couldn't match type `t' with `IntSet' -- and indeed, how do I tell the compiler that in the IntSet case s ~ t in the map signature? Shall I add more associated types, or "associated constraints" using ConstraintKinds? I tried and failed, at various stages, repeatedly. ...And then you discover that there is Set.cartesianProduct :: Set a -> Set b -> Set (a, b), but no equivalent in IntSet and things get even more grim. Cheers, Andrey

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RE: Container type classes
by Andrey Mokhov 30 May '19

30 May '19

> If you care about performance then explicit dictionary passing is > going to be worse than using type classes. Of course! But explicit dictionary passing works great for tests: the code size is reduced from O(#modules * #tests) when using the module system to O(#modules + #tests) when using dictionaries. For example, in the algebraic-graphs library, I have 500+ generic tests and around 10 modules. I don't want to write 5000 tests! Here is an example generic test which uses explicit dictionary passing: https://github.com/snowleopard/alga/blob/master/test/Algebra/Graph/Test/Gen…. I don't think it would be possible to reuse this test for different graph data types by using the module system instead of dictionaries. (Perhaps, Backpack could help? I don't know it very well.) Cheers, Andrey -----Original Message----- From: Matthew Pickering [mailto:matthewtpickering@gmail.com] Sent: 30 May 2019 18:26 To: Andrey Mokhov <andrey.mokhov(a)newcastle.ac.uk> Cc: ghc-devs(a)haskell.org; Andreas Klebinger <klebinger.andreas(a)gmx.at> Subject: Re: Container type classes If you care about performance then explicit dictionary passing is going to be worse than using type classes. At that point though, what do you gain from using the module system as you are just going to pass the same dictionaries into every function and never change them. So, for me, keep using modules but make the APIs of each module more consistent if you think it's worthwhile. On Thu, May 30, 2019 at 6:11 PM Andrey Mokhov <andrey.mokhov(a)newcastle.ac.uk> wrote: > > Hi all, > > I tried to use type classes for unifying APIs of several similar data structures and it didn't work well. (In my case I was working with graphs, instead of sets or maps.) > > First, you rarely want to be polymorphic over the set representation, because you care about performance. You really want to use that Very.Special.Set.insert because it has the right performance characteristics for your task at hand. I found only *one* use-case for writing polymorphic functions operating on something like IsSet: the testsuite. Of course, it is very nice to write a single property test like > > memberInsertProperty x set = (member x (insert x set) == True) > > and then use it for testing all set data structures that implement `member` and `insert`. Here you don't care about performance, only about correctness! > > However, this approach leads to problems with type inference, confusing error messages, and complexity. I found that it is much nicer to use explicit dictionary passing and write something like this instead: > > memberInsertProperty SetAPI{..} x set = (member x (insert x set) == True) > > where `member` and `insert` come from the SetAPI record via RecordWildCards. > > Finally, I'm not even sure how to create a type class covering Set and IntSet with the following two methods: > > singleton :: a -> Set a > map :: Ord b => (a -> b) -> Set a -> Set b > > singleton :: Int -> IntSet > map :: (Int -> Int) -> IntSet -> IntSet > > Could anyone please enlighten me about the right way to abstract over this using type classes? > > I tried a few approaches, for example: > > class IsSet s where > type Elem s > singleton :: Elem s -> s > map :: Ord (Elem t) => (Elem s -> Elem t) -> s -> t > > Looks nice, but I can't define the IntSet instance: > > instance IsSet IntSet where > type Elem IntSet = Int > singleton = IntSet.singleton > map = IntSet.map > > This fails with: Couldn't match type `t' with `IntSet' -- and indeed, how do I tell the compiler that in the IntSet case s ~ t in the map signature? Shall I add more associated types, or "associated constraints" using ConstraintKinds? I tried and failed, at various stages, repeatedly. > > ...And then you discover that there is Set.cartesianProduct :: Set a -> Set b -> Set (a, b), but no equivalent in IntSet and things get even more grim. > > Cheers, > Andrey > > _______________________________________________ > ghc-devs mailing list > ghc-devs(a)haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs

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