RE: Broken Data.Data instances
Alan, In that case, let's have a short feedback-loop between the two of us. It seems many of these files (Name.lhs, for example) are really stable through the repo-history. It would be nice to have one bigger refactoring all in one go (some of the code could use a polish, a lot of code seems removable). Regards, Philip Van: Alan Kim Zimmerman [alan.z...@gmail.com] Verzonden: vrijdag 25 juli 2014 13:44 Aan: Simon Peyton Jones CC: Holzenspies, P.K.F. (EWI); ghc-devs@haskell.org Onderwerp: Re: Broken Data.Data instances By the way, I would be happy to attempt this task, if the concept is viable. On Thu, Jul 24, 2014 at 11:23 PM, Alan Kim Zimmerman alan.z...@gmail.commailto:alan.z...@gmail.com wrote: While we are talking about fixing traversals, how about getting rid of the phase specific panic initialisers for placeHolderType, placeHolderKind and friends? In order to safely traverse with SYB, the following needs to be inserted into all the SYB schemes (see https://github.com/alanz/HaRe/blob/master/src/Language/Haskell/Refact/Utils/GhcUtils.hs) -- Check the Typeable items checkItemStage1 :: (Typeable a) = SYB.Stage - a - Bool checkItemStage1 stage x = (const False `SYB.extQ` postTcType `SYB.extQ` fixity `SYB.extQ` nameSet) x where nameSet = const (stage `elem` [SYB.Parser,SYB.TypeChecker]) :: GHC.NameSet - Bool postTcType = const (stage SYB.TypeChecker ) :: GHC.PostTcType- Bool fixity = const (stage SYB.Renamer ) :: GHC.Fixity- Bool And in addition HsCmdTop and ParStmtBlock are initialised with explicit 'undefined values. Perhaps use an initialiser that can have its panic turned off when called via the GHC API? Regards Alan On Thu, Jul 24, 2014 at 11:06 PM, Simon Peyton Jones simo...@microsoft.commailto:simo...@microsoft.com wrote: So... does anyone object to me changing these broken instances with the ones given by DeriveDataTypeable? That’s fine with me provided (a) the default behaviour is not immediate divergence (which it might well be), and (b) the pitfalls are documented. Simon From: Philip K.F. Hölzenspies [mailto:p.k.f.holzensp...@utwente.nlmailto:p.k.f.holzensp...@utwente.nl] Sent: 24 July 2014 18:42 To: Simon Peyton Jones Cc: ghc-devs@haskell.orgmailto:ghc-devs@haskell.org Subject: Re: Broken Data.Data instances Dear Simon, et al, These are very good points to make for people writing such traversals and queries. I would be more than happy to write a page on the pitfalls etc. on the wiki, but in my experience so far, exploring the innards of GHC is tremendously helped by trying small things out and showing (bits of) the intermediate structures. For me, personally, this has always been hindered by the absence of good instances of Data and/or Show (not having to bring DynFlags and not just visualising with the pretty printer are very helpful). So... does anyone object to me changing these broken instances with the ones given by DeriveDataTypeable? Also, many of these internal data structures could be provided with useful lenses to improve such traversals further. Anyone ever go at that? Would be people be interested? Regards, Philip [cid:image001.jpg@01CFA78B.7D356DE0] Simon Peyton Jonesmailto:simo...@microsoft.com 24 Jul 2014 18:22 GHC’s data structures are often mutually recursive. e.g. •The TyCon for Maybe contains the DataCon for Just •The DataCon For just contains Just’s type •Just’s type contains the TyCon for Maybe So any attempt to recursively walk over all these structures, as you would a tree, will fail. Also there’s a lot of sharing. For example, every occurrence of ‘map’ is a Var, and inside that Var is map’s type, its strictness, its rewrite RULE, etc etc. In walking over a term you may not want to walk over all that stuff at every occurrence of map. Maybe that’s it; I’m not certain since I did not write the Data instances for any of GHC’s types Simon From: ghc-devs [mailto:ghc-devs-boun...@haskell.org] On Behalf Of p.k.f.holzensp...@utwente.nlmailto:p.k.f.holzensp...@utwente.nl Sent: 24 July 2014 16:42 To: ghc-devs@haskell.orgmailto:ghc-devs@haskell.org Subject: Broken Data.Data instances Dear GHC-ers, Is there a reason for explicitly broken Data.Data instances? Case in point: instance Data Var where -- don't traverse? toConstr _ = abstractConstr Var gunfold _ _ = error gunfold dataTypeOf _ = mkNoRepType Var I understand (vaguely) arguments about abstract data types, but this also excludes convenient queries that can, e.g. extract all types from a CoreExpr. I had hoped to do stuff like this: collect :: (Typeable b, Data a, MonadPlus m) = a - m b collect = everything mplus $ mkQ mzero return allTypes :: CoreExpr - [Type] allTypes = collect Especially when still exploring (parts of) the GHC API, being able to extract things in this fashion is very
Re: Broken Data.Data instances
My intention would be to simply change the placeholders into something that would not blow up during a normal traversal, preferably something that still gives the required behaviour when invoked normally by GHC, to indicate a bug that needs fixing, but that can somehow be turned off at other tiimes. I am open to suggestions as to a mechanism that can achieve this, I thought of some kind of setting via Dynamic Flags. Alan On Sun, Jul 27, 2014 at 4:17 PM, p.k.f.holzensp...@utwente.nl wrote: Alan, In that case, let's have a short feedback-loop between the two of us. It seems many of these files (Name.lhs, for example) are really stable through the repo-history. It would be nice to have one bigger refactoring all in one go (some of the code could use a polish, a lot of code seems removable). Regards, Philip -- *Van:* Alan Kim Zimmerman [alan.z...@gmail.com] *Verzonden:* vrijdag 25 juli 2014 13:44 *Aan:* Simon Peyton Jones *CC:* Holzenspies, P.K.F. (EWI); ghc-devs@haskell.org *Onderwerp:* Re: Broken Data.Data instances By the way, I would be happy to attempt this task, if the concept is viable. On Thu, Jul 24, 2014 at 11:23 PM, Alan Kim Zimmerman alan.z...@gmail.com wrote: While we are talking about fixing traversals, how about getting rid of the phase specific panic initialisers for placeHolderType, placeHolderKind and friends? In order to safely traverse with SYB, the following needs to be inserted into all the SYB schemes (see https://github.com/alanz/HaRe/blob/master/src/Language/Haskell/Refact/Utils/GhcUtils.hs ) -- Check the Typeable items checkItemStage1 :: (Typeable a) = SYB.Stage - a - Bool checkItemStage1 stage x = (const False `SYB.extQ` postTcType `SYB.extQ` fixity `SYB.extQ` nameSet) x where nameSet = const (stage `elem` [SYB.Parser,SYB.TypeChecker]) :: GHC.NameSet - Bool postTcType = const (stage SYB.TypeChecker ) :: GHC.PostTcType- Bool fixity = const (stage SYB.Renamer ) :: GHC.Fixity- Bool And in addition HsCmdTop and ParStmtBlock are initialised with explicit 'undefined values. Perhaps use an initialiser that can have its panic turned off when called via the GHC API? Regards Alan On Thu, Jul 24, 2014 at 11:06 PM, Simon Peyton Jones simo...@microsoft.com wrote: So... does anyone object to me changing these broken instances with the ones given by DeriveDataTypeable? That’s fine with me provided (a) the default behaviour is not immediate divergence (which it might well be), and (b) the pitfalls are documented. Simon *From:* Philip K.F. Hölzenspies [mailto:p.k.f.holzensp...@utwente.nl] *Sent:* 24 July 2014 18:42 *To:* Simon Peyton Jones *Cc:* ghc-devs@haskell.org *Subject:* Re: Broken Data.Data instances Dear Simon, et al, These are very good points to make for people writing such traversals and queries. I would be more than happy to write a page on the pitfalls etc. on the wiki, but in my experience so far, exploring the innards of GHC is tremendously helped by trying small things out and showing (bits of) the intermediate structures. For me, personally, this has always been hindered by the absence of good instances of Data and/or Show (not having to bring DynFlags and not just visualising with the pretty printer are very helpful). So... does anyone object to me changing these broken instances with the ones given by DeriveDataTypeable? Also, many of these internal data structures could be provided with useful lenses to improve such traversals further. Anyone ever go at that? Would be people be interested? Regards, Philip *Simon Peyton Jones* simo...@microsoft.com 24 Jul 2014 18:22 GHC’s data structures are often mutually recursive. e.g. ·The TyCon for Maybe contains the DataCon for Just ·The DataCon For just contains Just’s type ·Just’s type contains the TyCon for Maybe So any attempt to recursively walk over all these structures, as you would a tree, will fail. Also there’s a lot of sharing. For example, every occurrence of ‘map’ is a Var, and inside that Var is map’s type, its strictness, its rewrite RULE, etc etc. In walking over a term you may not want to walk over all that stuff at every occurrence of map. Maybe that’s it; I’m not certain since I did not write the Data instances for any of GHC’s types Simon *From:* ghc-devs [mailto:ghc-devs-boun...@haskell.org ghc-devs-boun...@haskell.org] *On Behalf Of * p.k.f.holzensp...@utwente.nl *Sent:* 24 July 2014 16:42 *To:* ghc-devs@haskell.org *Subject:* Broken Data.Data instances Dear GHC-ers, Is there a reason for explicitly broken Data.Data instances? Case in point: instance Data Var where -- don't traverse? toConstr _ = abstractConstr Var gunfold _ _ = error gunfold dataTypeOf _ = mkNoRepType Var
Re: phabricator issue with git submodules.
Hello Edward, I've done that, see https://phabricator.haskell.org/D96 -- but now I'm curious but since this is done in this way, basically speaking library/unix + libraries/primitive now points to commits done in my forks of those libs on github.com waiting for approval since I already pushed appropriate pull requests. Now this also means that D96 is probably not includable in GHC HEAD since it points to currently non-existing patches (in public libraries/unix + primitive). Am I right that this works in this way? Thanks, Karel On 07/26/14 09:39 PM, Edward Z. Yang wrote: Hello Karel, When your submodules get updated, you need to add them to your commit (since the parent repository maintains pointers to the submodules). Then they will no longer show up as dirty and you can submit the Phabricator patch. Edward Excerpts from Karel Gardas's message of 2014-07-25 22:48:21 +0100: Hi, just fixing few warning issues on Solaris/x86. The changes spread over main ghc tree and libraries/primitive and libraries/unix. I already commited changes and pushed to my github.com's forks of libraries/primitive and libraries/unix. The git status looks then: $ git status On branch master Your branch is ahead of 'origin/master' by 2 commits. (use git push to publish your local commits) Changes not staged for commit: (use git addfile... to update what will be committed) (use git checkout --file... to discard changes in working directory) modified: libraries/primitive (new commits) modified: libraries/unix (new commits) no changes added to commit (use git add and/or git commit -a) and yet phabricator still complains about it: $ arc diff You have unstaged changes in this working copy. Working copy: /export/home/karel/vcs/ghc-src/validate-fixes/ Unstaged changes in working copy: libraries/primitive libraries/unix Do you want to amend these files to the commit? [y/N] Usage Exception: Stage and commit (or revert) them before proceeding. I pressed enter in question above. Is that a known issue or am I doing something wrong here? Thanks! Karel ___ ghc-devs mailing list ghc-devs@haskell.org http://www.haskell.org/mailman/listinfo/ghc-devs
Re: phabricator issue with git submodules.
That's right. I am actually not even sure how Harbormaster even manages to find your commits for the build... Edward Excerpts from Karel Gardas's message of 2014-07-27 18:02:24 +0100: Hello Edward, I've done that, see https://phabricator.haskell.org/D96 -- but now I'm curious but since this is done in this way, basically speaking library/unix + libraries/primitive now points to commits done in my forks of those libs on github.com waiting for approval since I already pushed appropriate pull requests. Now this also means that D96 is probably not includable in GHC HEAD since it points to currently non-existing patches (in public libraries/unix + primitive). Am I right that this works in this way? Thanks, Karel On 07/26/14 09:39 PM, Edward Z. Yang wrote: Hello Karel, When your submodules get updated, you need to add them to your commit (since the parent repository maintains pointers to the submodules). Then they will no longer show up as dirty and you can submit the Phabricator patch. Edward Excerpts from Karel Gardas's message of 2014-07-25 22:48:21 +0100: Hi, just fixing few warning issues on Solaris/x86. The changes spread over main ghc tree and libraries/primitive and libraries/unix. I already commited changes and pushed to my github.com's forks of libraries/primitive and libraries/unix. The git status looks then: $ git status On branch master Your branch is ahead of 'origin/master' by 2 commits. (use git push to publish your local commits) Changes not staged for commit: (use git addfile... to update what will be committed) (use git checkout --file... to discard changes in working directory) modified: libraries/primitive (new commits) modified: libraries/unix (new commits) no changes added to commit (use git add and/or git commit -a) and yet phabricator still complains about it: $ arc diff You have unstaged changes in this working copy. Working copy: /export/home/karel/vcs/ghc-src/validate-fixes/ Unstaged changes in working copy: libraries/primitive libraries/unix Do you want to amend these files to the commit? [y/N] Usage Exception: Stage and commit (or revert) them before proceeding. I pressed enter in question above. Is that a known issue or am I doing something wrong here? Thanks! Karel ___ ghc-devs mailing list ghc-devs@haskell.org http://www.haskell.org/mailman/listinfo/ghc-devs
Re: Broken Data.Data instances
To my knowledge there is no trac ticket to make the AST safe. Is this correct? Can I make one? Alan On Sun, Jul 27, 2014 at 4:28 PM, Alan Kim Zimmerman alan.z...@gmail.com wrote: My intention would be to simply change the placeholders into something that would not blow up during a normal traversal, preferably something that still gives the required behaviour when invoked normally by GHC, to indicate a bug that needs fixing, but that can somehow be turned off at other tiimes. I am open to suggestions as to a mechanism that can achieve this, I thought of some kind of setting via Dynamic Flags. Alan On Sun, Jul 27, 2014 at 4:17 PM, p.k.f.holzensp...@utwente.nl wrote: Alan, In that case, let's have a short feedback-loop between the two of us. It seems many of these files (Name.lhs, for example) are really stable through the repo-history. It would be nice to have one bigger refactoring all in one go (some of the code could use a polish, a lot of code seems removable). Regards, Philip -- *Van:* Alan Kim Zimmerman [alan.z...@gmail.com] *Verzonden:* vrijdag 25 juli 2014 13:44 *Aan:* Simon Peyton Jones *CC:* Holzenspies, P.K.F. (EWI); ghc-devs@haskell.org *Onderwerp:* Re: Broken Data.Data instances By the way, I would be happy to attempt this task, if the concept is viable. On Thu, Jul 24, 2014 at 11:23 PM, Alan Kim Zimmerman alan.z...@gmail.com wrote: While we are talking about fixing traversals, how about getting rid of the phase specific panic initialisers for placeHolderType, placeHolderKind and friends? In order to safely traverse with SYB, the following needs to be inserted into all the SYB schemes (see https://github.com/alanz/HaRe/blob/master/src/Language/Haskell/Refact/Utils/GhcUtils.hs ) -- Check the Typeable items checkItemStage1 :: (Typeable a) = SYB.Stage - a - Bool checkItemStage1 stage x = (const False `SYB.extQ` postTcType `SYB.extQ` fixity `SYB.extQ` nameSet) x where nameSet = const (stage `elem` [SYB.Parser,SYB.TypeChecker]) :: GHC.NameSet - Bool postTcType = const (stage SYB.TypeChecker ) :: GHC.PostTcType- Bool fixity = const (stage SYB.Renamer ) :: GHC.Fixity- Bool And in addition HsCmdTop and ParStmtBlock are initialised with explicit 'undefined values. Perhaps use an initialiser that can have its panic turned off when called via the GHC API? Regards Alan On Thu, Jul 24, 2014 at 11:06 PM, Simon Peyton Jones simo...@microsoft.com wrote: So... does anyone object to me changing these broken instances with the ones given by DeriveDataTypeable? That’s fine with me provided (a) the default behaviour is not immediate divergence (which it might well be), and (b) the pitfalls are documented. Simon *From:* Philip K.F. Hölzenspies [mailto:p.k.f.holzensp...@utwente.nl] *Sent:* 24 July 2014 18:42 *To:* Simon Peyton Jones *Cc:* ghc-devs@haskell.org *Subject:* Re: Broken Data.Data instances Dear Simon, et al, These are very good points to make for people writing such traversals and queries. I would be more than happy to write a page on the pitfalls etc. on the wiki, but in my experience so far, exploring the innards of GHC is tremendously helped by trying small things out and showing (bits of) the intermediate structures. For me, personally, this has always been hindered by the absence of good instances of Data and/or Show (not having to bring DynFlags and not just visualising with the pretty printer are very helpful). So... does anyone object to me changing these broken instances with the ones given by DeriveDataTypeable? Also, many of these internal data structures could be provided with useful lenses to improve such traversals further. Anyone ever go at that? Would be people be interested? Regards, Philip *Simon Peyton Jones* simo...@microsoft.com 24 Jul 2014 18:22 GHC’s data structures are often mutually recursive. e.g. ·The TyCon for Maybe contains the DataCon for Just ·The DataCon For just contains Just’s type ·Just’s type contains the TyCon for Maybe So any attempt to recursively walk over all these structures, as you would a tree, will fail. Also there’s a lot of sharing. For example, every occurrence of ‘map’ is a Var, and inside that Var is map’s type, its strictness, its rewrite RULE, etc etc. In walking over a term you may not want to walk over all that stuff at every occurrence of map. Maybe that’s it; I’m not certain since I did not write the Data instances for any of GHC’s types Simon *From:* ghc-devs [mailto:ghc-devs-boun...@haskell.org ghc-devs-boun...@haskell.org] *On Behalf Of * p.k.f.holzensp...@utwente.nl *Sent:* 24 July 2014 16:42 *To:* ghc-devs@haskell.org *Subject:* Broken Data.Data instances Dear GHC-ers, Is there a reason for explicitly broken
Re: Broken Data.Data instances
Philip, Alan, If you need a hand, I'm happy to pitch in guidance. I've had to mangle a bunch of hand-written Data instances and push out patches to a dozen packages that used to be built this way before I convinced the authors to switch to safer versions of Data. Using virtual smart constructors like we do now in containers and Text where needed can be used to preserve internal invariants, etc. This works far better for users of the API than just randomly throwing them a live hand grenade. As I recall, these little grenades in generic programming over the GHC API have been a constant source of pain for libraries like haddock. Simon, It seems to me that regarding circular data structures, nothing prevents you from walking a circular data structure with Data.Data. You can generate a new one productively that looks just like the old with the contents swapped out, it is indistinguishable to an observer if the fixed point is lost, and a clever observer can use observable sharing to get it back, supposing that they are allowed to try. Alternately, we could use the 'virtual constructor' trick there to break the cycle and reintroduce it, but I'm less enthusiastic about that idea, even if it is simpler in many ways. -Edward On Sun, Jul 27, 2014 at 10:17 AM, p.k.f.holzensp...@utwente.nl wrote: Alan, In that case, let's have a short feedback-loop between the two of us. It seems many of these files (Name.lhs, for example) are really stable through the repo-history. It would be nice to have one bigger refactoring all in one go (some of the code could use a polish, a lot of code seems removable). Regards, Philip -- *Van:* Alan Kim Zimmerman [alan.z...@gmail.com] *Verzonden:* vrijdag 25 juli 2014 13:44 *Aan:* Simon Peyton Jones *CC:* Holzenspies, P.K.F. (EWI); ghc-devs@haskell.org *Onderwerp:* Re: Broken Data.Data instances By the way, I would be happy to attempt this task, if the concept is viable. On Thu, Jul 24, 2014 at 11:23 PM, Alan Kim Zimmerman alan.z...@gmail.com wrote: While we are talking about fixing traversals, how about getting rid of the phase specific panic initialisers for placeHolderType, placeHolderKind and friends? In order to safely traverse with SYB, the following needs to be inserted into all the SYB schemes (see https://github.com/alanz/HaRe/blob/master/src/Language/Haskell/Refact/Utils/GhcUtils.hs ) -- Check the Typeable items checkItemStage1 :: (Typeable a) = SYB.Stage - a - Bool checkItemStage1 stage x = (const False `SYB.extQ` postTcType `SYB.extQ` fixity `SYB.extQ` nameSet) x where nameSet = const (stage `elem` [SYB.Parser,SYB.TypeChecker]) :: GHC.NameSet - Bool postTcType = const (stage SYB.TypeChecker ) :: GHC.PostTcType- Bool fixity = const (stage SYB.Renamer ) :: GHC.Fixity- Bool And in addition HsCmdTop and ParStmtBlock are initialised with explicit 'undefined values. Perhaps use an initialiser that can have its panic turned off when called via the GHC API? Regards Alan On Thu, Jul 24, 2014 at 11:06 PM, Simon Peyton Jones simo...@microsoft.com wrote: So... does anyone object to me changing these broken instances with the ones given by DeriveDataTypeable? That’s fine with me provided (a) the default behaviour is not immediate divergence (which it might well be), and (b) the pitfalls are documented. Simon *From:* Philip K.F. Hölzenspies [mailto:p.k.f.holzensp...@utwente.nl] *Sent:* 24 July 2014 18:42 *To:* Simon Peyton Jones *Cc:* ghc-devs@haskell.org *Subject:* Re: Broken Data.Data instances Dear Simon, et al, These are very good points to make for people writing such traversals and queries. I would be more than happy to write a page on the pitfalls etc. on the wiki, but in my experience so far, exploring the innards of GHC is tremendously helped by trying small things out and showing (bits of) the intermediate structures. For me, personally, this has always been hindered by the absence of good instances of Data and/or Show (not having to bring DynFlags and not just visualising with the pretty printer are very helpful). So... does anyone object to me changing these broken instances with the ones given by DeriveDataTypeable? Also, many of these internal data structures could be provided with useful lenses to improve such traversals further. Anyone ever go at that? Would be people be interested? Regards, Philip *Simon Peyton Jones* simo...@microsoft.com 24 Jul 2014 18:22 GHC’s data structures are often mutually recursive. e.g. ·The TyCon for Maybe contains the DataCon for Just ·The DataCon For just contains Just’s type ·Just’s type contains the TyCon for Maybe So any attempt to recursively walk over all these structures, as you would a tree, will fail. Also there’s a lot of sharing. For example,
Re: Broken Data.Data instances
Philip How would you like to take this forward? From my side I would appreciate all guidance/help to get it resolved, it is a huge hindrance for HaRe. Alan On Sun, Jul 27, 2014 at 7:27 PM, Edward Kmett ekm...@gmail.com wrote: Philip, Alan, If you need a hand, I'm happy to pitch in guidance. I've had to mangle a bunch of hand-written Data instances and push out patches to a dozen packages that used to be built this way before I convinced the authors to switch to safer versions of Data. Using virtual smart constructors like we do now in containers and Text where needed can be used to preserve internal invariants, etc. This works far better for users of the API than just randomly throwing them a live hand grenade. As I recall, these little grenades in generic programming over the GHC API have been a constant source of pain for libraries like haddock. Simon, It seems to me that regarding circular data structures, nothing prevents you from walking a circular data structure with Data.Data. You can generate a new one productively that looks just like the old with the contents swapped out, it is indistinguishable to an observer if the fixed point is lost, and a clever observer can use observable sharing to get it back, supposing that they are allowed to try. Alternately, we could use the 'virtual constructor' trick there to break the cycle and reintroduce it, but I'm less enthusiastic about that idea, even if it is simpler in many ways. -Edward On Sun, Jul 27, 2014 at 10:17 AM, p.k.f.holzensp...@utwente.nl wrote: Alan, In that case, let's have a short feedback-loop between the two of us. It seems many of these files (Name.lhs, for example) are really stable through the repo-history. It would be nice to have one bigger refactoring all in one go (some of the code could use a polish, a lot of code seems removable). Regards, Philip -- *Van:* Alan Kim Zimmerman [alan.z...@gmail.com] *Verzonden:* vrijdag 25 juli 2014 13:44 *Aan:* Simon Peyton Jones *CC:* Holzenspies, P.K.F. (EWI); ghc-devs@haskell.org *Onderwerp:* Re: Broken Data.Data instances By the way, I would be happy to attempt this task, if the concept is viable. On Thu, Jul 24, 2014 at 11:23 PM, Alan Kim Zimmerman alan.z...@gmail.com wrote: While we are talking about fixing traversals, how about getting rid of the phase specific panic initialisers for placeHolderType, placeHolderKind and friends? In order to safely traverse with SYB, the following needs to be inserted into all the SYB schemes (see https://github.com/alanz/HaRe/blob/master/src/Language/Haskell/Refact/Utils/GhcUtils.hs ) -- Check the Typeable items checkItemStage1 :: (Typeable a) = SYB.Stage - a - Bool checkItemStage1 stage x = (const False `SYB.extQ` postTcType `SYB.extQ` fixity `SYB.extQ` nameSet) x where nameSet = const (stage `elem` [SYB.Parser,SYB.TypeChecker]) :: GHC.NameSet - Bool postTcType = const (stage SYB.TypeChecker ) :: GHC.PostTcType- Bool fixity = const (stage SYB.Renamer ) :: GHC.Fixity- Bool And in addition HsCmdTop and ParStmtBlock are initialised with explicit 'undefined values. Perhaps use an initialiser that can have its panic turned off when called via the GHC API? Regards Alan On Thu, Jul 24, 2014 at 11:06 PM, Simon Peyton Jones simo...@microsoft.com wrote: So... does anyone object to me changing these broken instances with the ones given by DeriveDataTypeable? That’s fine with me provided (a) the default behaviour is not immediate divergence (which it might well be), and (b) the pitfalls are documented. Simon *From:* Philip K.F. Hölzenspies [mailto:p.k.f.holzensp...@utwente.nl] *Sent:* 24 July 2014 18:42 *To:* Simon Peyton Jones *Cc:* ghc-devs@haskell.org *Subject:* Re: Broken Data.Data instances Dear Simon, et al, These are very good points to make for people writing such traversals and queries. I would be more than happy to write a page on the pitfalls etc. on the wiki, but in my experience so far, exploring the innards of GHC is tremendously helped by trying small things out and showing (bits of) the intermediate structures. For me, personally, this has always been hindered by the absence of good instances of Data and/or Show (not having to bring DynFlags and not just visualising with the pretty printer are very helpful). So... does anyone object to me changing these broken instances with the ones given by DeriveDataTypeable? Also, many of these internal data structures could be provided with useful lenses to improve such traversals further. Anyone ever go at that? Would be people be interested? Regards, Philip *Simon Peyton Jones* simo...@microsoft.com 24 Jul 2014 18:22 GHC’s data structures are often mutually recursive. e.g. ·The TyCon for Maybe contains the DataCon for
Re: Broken Data.Data instances
What if there is a good reason for a missing/broken Data.Data instance? I'm specifically thinking of GADTs. There are few currently, but I, for one, have toyed with the idea of adding more. My recollection is that Data.Data doesn't work with GADTs. As a concrete, existent example, see CoAxiom.BranchList, which allows for type-level reification of singleton lists as distinct from other, not-necessarily-singleton lists. I would very much like to support API usage that would benefit from working Data.Data instances, but I also want to be sure we're not eliminating other possible futures without due discussion. Richard On Jul 27, 2014, at 2:04 PM, Alan Kim Zimmerman alan.z...@gmail.com wrote: Philip How would you like to take this forward? From my side I would appreciate all guidance/help to get it resolved, it is a huge hindrance for HaRe. Alan On Sun, Jul 27, 2014 at 7:27 PM, Edward Kmett ekm...@gmail.com wrote: Philip, Alan, If you need a hand, I'm happy to pitch in guidance. I've had to mangle a bunch of hand-written Data instances and push out patches to a dozen packages that used to be built this way before I convinced the authors to switch to safer versions of Data. Using virtual smart constructors like we do now in containers and Text where needed can be used to preserve internal invariants, etc. This works far better for users of the API than just randomly throwing them a live hand grenade. As I recall, these little grenades in generic programming over the GHC API have been a constant source of pain for libraries like haddock. Simon, It seems to me that regarding circular data structures, nothing prevents you from walking a circular data structure with Data.Data. You can generate a new one productively that looks just like the old with the contents swapped out, it is indistinguishable to an observer if the fixed point is lost, and a clever observer can use observable sharing to get it back, supposing that they are allowed to try. Alternately, we could use the 'virtual constructor' trick there to break the cycle and reintroduce it, but I'm less enthusiastic about that idea, even if it is simpler in many ways. -Edward On Sun, Jul 27, 2014 at 10:17 AM, p.k.f.holzensp...@utwente.nl wrote: Alan, In that case, let's have a short feedback-loop between the two of us. It seems many of these files (Name.lhs, for example) are really stable through the repo-history. It would be nice to have one bigger refactoring all in one go (some of the code could use a polish, a lot of code seems removable). Regards, Philip Van: Alan Kim Zimmerman [alan.z...@gmail.com] Verzonden: vrijdag 25 juli 2014 13:44 Aan: Simon Peyton Jones CC: Holzenspies, P.K.F. (EWI); ghc-devs@haskell.org Onderwerp: Re: Broken Data.Data instances By the way, I would be happy to attempt this task, if the concept is viable. On Thu, Jul 24, 2014 at 11:23 PM, Alan Kim Zimmerman alan.z...@gmail.com wrote: While we are talking about fixing traversals, how about getting rid of the phase specific panic initialisers for placeHolderType, placeHolderKind and friends? In order to safely traverse with SYB, the following needs to be inserted into all the SYB schemes (see https://github.com/alanz/HaRe/blob/master/src/Language/Haskell/Refact/Utils/GhcUtils.hs) -- Check the Typeable items checkItemStage1 :: (Typeable a) = SYB.Stage - a - Bool checkItemStage1 stage x = (const False `SYB.extQ` postTcType `SYB.extQ` fixity `SYB.extQ` nameSet) x where nameSet = const (stage `elem` [SYB.Parser,SYB.TypeChecker]) :: GHC.NameSet - Bool postTcType = const (stage SYB.TypeChecker ) :: GHC.PostTcType- Bool fixity = const (stage SYB.Renamer ) :: GHC.Fixity- Bool And in addition HsCmdTop and ParStmtBlock are initialised with explicit 'undefined values. Perhaps use an initialiser that can have its panic turned off when called via the GHC API? Regards Alan On Thu, Jul 24, 2014 at 11:06 PM, Simon Peyton Jones simo...@microsoft.com wrote: So... does anyone object to me changing these broken instances with the ones given by DeriveDataTypeable? That’s fine with me provided (a) the default behaviour is not immediate divergence (which it might well be), and (b) the pitfalls are documented. Simon From: Philip K.F. Hölzenspies [mailto:p.k.f.holzensp...@utwente.nl] Sent: 24 July 2014 18:42 To: Simon Peyton Jones Cc: ghc-devs@haskell.org Subject: Re: Broken Data.Data instances Dear Simon, et al, These are very good points to make for people writing such traversals and queries. I would be more than happy to write a page on the pitfalls etc. on the wiki, but in my experience so far, exploring the innards of GHC is tremendously helped by trying small things out and showing (bits of) the
Re: Broken Data.Data instances
Im mostly looking at the Data.Data stuff as nice to have at this point. Well, it really is need to have for some users, but they can typically get by by writing a few hundred lines of boilerplate when its not there. If you need to break something internally and it costs us a Data instance for something? Have at it. If we can still hack around the changes with Data then great. Otherwise the Data machinery has always been for expert users who already deal with a great deal of breakage anyways, so thrashing on that API seems fine to me. Not desirable, but not unexpected. -Edward On Sun, Jul 27, 2014 at 9:49 PM, Richard Eisenberg e...@cis.upenn.edu wrote: What if there is a good reason for a missing/broken Data.Data instance? I'm specifically thinking of GADTs. There are few currently, but I, for one, have toyed with the idea of adding more. My recollection is that Data.Data doesn't work with GADTs. As a concrete, existent example, see CoAxiom.BranchList, which allows for type-level reification of singleton lists as distinct from other, not-necessarily-singleton lists. I would very much like to support API usage that would benefit from working Data.Data instances, but I also want to be sure we're not eliminating other possible futures without due discussion. Richard On Jul 27, 2014, at 2:04 PM, Alan Kim Zimmerman alan.z...@gmail.com wrote: Philip How would you like to take this forward? From my side I would appreciate all guidance/help to get it resolved, it is a huge hindrance for HaRe. Alan On Sun, Jul 27, 2014 at 7:27 PM, Edward Kmett ekm...@gmail.com wrote: Philip, Alan, If you need a hand, I'm happy to pitch in guidance. I've had to mangle a bunch of hand-written Data instances and push out patches to a dozen packages that used to be built this way before I convinced the authors to switch to safer versions of Data. Using virtual smart constructors like we do now in containers and Text where needed can be used to preserve internal invariants, etc. This works far better for users of the API than just randomly throwing them a live hand grenade. As I recall, these little grenades in generic programming over the GHC API have been a constant source of pain for libraries like haddock. Simon, It seems to me that regarding circular data structures, nothing prevents you from walking a circular data structure with Data.Data. You can generate a new one productively that looks just like the old with the contents swapped out, it is indistinguishable to an observer if the fixed point is lost, and a clever observer can use observable sharing to get it back, supposing that they are allowed to try. Alternately, we could use the 'virtual constructor' trick there to break the cycle and reintroduce it, but I'm less enthusiastic about that idea, even if it is simpler in many ways. -Edward On Sun, Jul 27, 2014 at 10:17 AM, p.k.f.holzensp...@utwente.nl wrote: Alan, In that case, let's have a short feedback-loop between the two of us. It seems many of these files (Name.lhs, for example) are really stable through the repo-history. It would be nice to have one bigger refactoring all in one go (some of the code could use a polish, a lot of code seems removable). Regards, Philip -- *Van:* Alan Kim Zimmerman [alan.z...@gmail.com] *Verzonden:* vrijdag 25 juli 2014 13:44 *Aan:* Simon Peyton Jones *CC:* Holzenspies, P.K.F. (EWI); ghc-devs@haskell.org *Onderwerp:* Re: Broken Data.Data instances By the way, I would be happy to attempt this task, if the concept is viable. On Thu, Jul 24, 2014 at 11:23 PM, Alan Kim Zimmerman alan.z...@gmail.com wrote: While we are talking about fixing traversals, how about getting rid of the phase specific panic initialisers for placeHolderType, placeHolderKind and friends? In order to safely traverse with SYB, the following needs to be inserted into all the SYB schemes (see https://github.com/alanz/HaRe/blob/master/src/Language/Haskell/Refact/Utils/GhcUtils.hs ) -- Check the Typeable items checkItemStage1 :: (Typeable a) = SYB.Stage - a - Bool checkItemStage1 stage x = (const False `SYB.extQ` postTcType `SYB.extQ` fixity `SYB.extQ` nameSet) x where nameSet = const (stage `elem` [SYB.Parser,SYB.TypeChecker]) :: GHC.NameSet - Bool postTcType = const (stage SYB.TypeChecker ) :: GHC.PostTcType- Bool fixity = const (stage SYB.Renamer ) :: GHC.Fixity- Bool And in addition HsCmdTop and ParStmtBlock are initialised with explicit 'undefined values. Perhaps use an initialiser that can have its panic turned off when called via the GHC API? Regards Alan On Thu, Jul 24, 2014 at 11:06 PM, Simon Peyton Jones simo...@microsoft.com wrote: So... does anyone object to me changing these broken instances with the ones given by DeriveDataTypeable? That’s fine with me
