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RE: Hoopl and Arrows
by Simon Peyton Jones 02 Mar '15

02 Mar '15

Thomas Hoopl works on control flow graphs, whereas Core is lambda calculus. I really don’t think Hoopl is going to be any good for optimising Core. Ask the ghc-devs mailing list too. Someone there has been writing about arrows recently (take a look at the archive). Simon From: Thomas Bereknyei [mailto:tomberek@gmail.com] Sent: 02 March 2015 17:07 To: nr(a)cs.tufts.edu; Simon Peyton Jones Subject: Hoopl and Arrows I've been interested in Arrows and their optimization recently. I've run into problems during basic tooling so I built a quasiquoter for proc notation (still working on rec and let statements, but the rest of it works) that converts from haskell-src-exts into a desugarred TH format. My original goal was to implement "Casual Commutative Arrows" [1] but to make it more user friendly and to include arrows with effects. I came across Hoopl and at first glance I would think it can help with Arrow optimization, especially with the tuple shuffling from desuggared proc-do notation. In spite of the slogan of "Hoopl: Dataflow Optimization made Simple" and the git repo's testing folder, I'm not 100% clear on Hoopl usage. I would be interested in anything that can get me started or even a thought or two whether it would be worth looking into for Arrows. Simon, regarding [2], my quasiquoter can be rewritten to take `bind`, `bind_`, `fixA`, and `ifThenElseA` from scope rather than being built in. Would that help with #7828? I am not very familiar with GHC internals at the moment, and I am confused about the complexity of dsArrows.hs in contrast with my own parser. It seems I have a good start on it in the Parser module at [3], WARNING: untested and rough draft code, though suggestions and pointers are welcome. I was thinking of sending some of my code to haskell-src-meta because they can't yet translate their version of Exp into TH's ExpQ. -Tom [1] (https://hackage.haskell.org/package/CCA) [2] (https://ghc.haskell.org/trac/ghc/ticket/7828#comment:54) [3] (https://www.fpcomplete.com/user/tomberek/rulestesting)

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Fwd: EvTerms and how they are used
by Jan Bracker 02 Mar '15

02 Mar '15

Hi Adam, thank you for your quick and detailed answer! I think I understand how to construct evidence for typeclass constraints now. But trying to apply this, I still have some problems. I have something along the following lines: class Polymonad m n p where -- Functions instance Polymonad Identity Identity Identity where -- Implementation -- Further instances and some small chunk of code involving them: The code implies the following constraint: Polymonad Identity n_abpq Identity As the ambiguity error I get says, when trying to compile this: There is only one matching instance (the one above, lets call it $fPolymonadIdentityIdentityIdentity). So my plugin tries to tell GHC to use that instance. As far as I understand it, since the parameters of $fPolymonadIdentityIdentityIdentity are no type variables and there is no superclass it should be as easy as saying: EvDFunApp $fPolymonadIdentityIdentityIdentity [] [] But when I run this with -dcore-lint I get the following error message: *** Core Lint errors : in result of Desugar (after optimization) *** <no location info>: Warning: In the expression: >> @ Identity @ Any @ Identity $fPolymonadIdentityIdentityIdentity @ () @ () (idOp @ Bool True) (>>= @ Identity @ Identity @ Any $fPolymonadIdentityIdentityIdentity @ Char @ () (return @ Char @ Identity $fPolymonadIdentityIdentityIdentity (C# 'a')) (\ _ [Occ=Dead] -> return @ () @ Identity $fPolymonadIdentityIdentityIdentity ())) Argument value doesn't match argument type: Fun type: Polymonad Identity Any Identity => forall a_abdV[sk] b_abdW[sk]. Identity a_abdV[sk] -> Any b_abdW[sk] -> Identity b_abdW[sk] Arg type: Polymonad Identity Identity Identity Arg: $fPolymonadIdentityIdentityIdentity What am I missing? Why doesn't the argument type "Polymonad Identity Identity Identity" match the first argument of the function type "Polymonad Identity Any Identity => forall a_abdV[sk] b_abdW[sk]. Identity a_abdV[sk] -> Any b_abdW[sk] -> Identity b_abdW[sk]". Why is the type variable translated to "Any"? Best, Jan 2015-02-25 13:35 GMT+00:00 Adam Gundry <adam(a)well-typed.com>: > Hi Jan, > > Yes, unfortunately the meaning of EvTerm is a weak point of the current > typechecker plugins story; it rather requires one to understand how > GHC's constraint solver produces evidence. There are lots of papers on > evidence for equality constraints in System FC, but typeclass > constraints are generally ignored as they are just datatypes at the FC > level. > > Let me try to give you some idea of what EvDFunApp means, then hopefully > those with more knowledge of the GHC internals can correct me... > > If you write a class instance, e.g. > > instance (Show a, Show b) => Show (T a b) where ... > > then GHC generates a dfun (short for "dictionary function", I guess) > > $fShowT :: forall a b . (Show a, Show b) => Show (T a b) > > where Show is treated as a record data type containing a dictionary of > methods for the class. At the core level, this is a normal term-level > function (albeit with a strange name). > > Now when the typechecker has a constraint to solve, say > > Show (T Int Bool), > > it produces evidence for this by applying $fShowT to the appropriate > types and to evidence for the superclass constraints, in this case > something like > > $fShowT @Int @Bool $fShowInt $fShowBool > > where I'm using @ for type application. This is represented in EvTerm as > > EvDFunApp $fShowT [Int, Bool] [ EvDFunApp $fShowInt [] [] > , EvDFunApp $fShowBool [] [] ] > > Thus the [Type] is the list of kinds/types at which to instantiate the > dfun, and the [EvTerm] is the list of evidence terms to which it must be > applied. Obviously this application should be well-typed, and > -dcore-lint will complain if it is not. > > For typechecker plugins, it would be nice if we could write arbitrary > core expressions as evidence, but this hasn't yet been implemented > (partially because most of the examples so far solve equality > constraints, rather than typeclass constraints). > > Hope this helps, > > Adam > > > On 25/02/15 10:55, Jan Bracker wrote: > > Hello, > > > > I am trying to use the new type checker plugins [1] that are implemented > > in head. > > > > When successful a plugin has to return a [(EvTerm, Ct)] for the solved > > constraints. The documentation on EvTerms is scarce [2,3,4] and I could > > not find papers that explain them (many talk about 'evidence', but they > > never get concrete). > > > > So far I have figured out that "EvDFunApp DFunId [Type] [EvTerm]" > > selects a certain instance to be used for a constraint, though I don't > > know what the list of EvTerms in the end is for. I am also a bit unclear > > on how the "[Type]" is used.If I turn on '-dcore-lint' I get errors. So > > I still seem to be using it wrong. > > > > I have also asked in IRC, but did not get a response to my question. > > > > I am sorry if this is the wrong mailing list to ask. If there is a more > > apropriate place just point it out. > > > > Best, > > Jan > > > > [1]: https://ghc.haskell.org/trac/ghc/wiki/Plugins/TypeChecker > > [2]: > http://haskell.inf.elte.hu/docs/7.11.20150225.noWin32/html/libraries/ghc-7.… > > [3]: > http://haskell.inf.elte.hu/docs/7.11.20150225.noWin32/html/libraries/ghc-7.… > > [4]: > http://haskell.inf.elte.hu/docs/7.11.20150225.noWin32/html/users_guide/comp… > > > -- > Adam Gundry, Haskell Consultant > Well-Typed LLP, http://www.well-typed.com/ >

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Allowing rules to depend upon SimplCont
by Ben Gamari 02 Mar '15

02 Mar '15

In Bug #9661, Comment #12 Simon Peyton-Jones wrote [1], > Annoyingly, the `CoreSyn.RuleFun` API for built-in rules does not give > access to the context of an application (the `SimplCont`), but it > would not be hard to make it do so. > > So if that is the right rewrite, then it'd be another useful project > for someone. I started taking a look at this over the weekend, hoping for a weekend-ish project. Unfortunately it's not as easy as it initially looked. The current state of my work can be found here [2]. The core of the change (as I understand it) is to add a `SimplCont` argument to `RuleFun` [3] although things are in actuality a bit more complicated While it was easy to pipe through the `SimplCont` in the simplifier itself (as it was already keeping track of the `SimplCont` context), `ruleCheck` in `Rules.hs` does not know anything about the simplifier or `SimplCont`. Currently `ruleCheck` is quite simple: It traverses the program examining function applications, looking for rules which apply to the applied function and match a user-specified predicate. It then produces a human-readable message in the event that the rule would not fire. Unfortunately, to evaluate whether the rule will fire we actually need to try calling the `RuleFun`, which now requires having a `SimplCont`. As far as I can tell there are three ways to address this, 1. Pass a dummy `SimplCont` (probably a `Stop`) to the `RuleFun`. This is by far the easiest option but will result in discrepancies between the rule check and the rules actually fired by simplifier. 2. Replicate the simplifier's logic to produce a `SimplCont` in the rule check. This seems like it will result in a great deal of unnecessary (and non-trivial) code duplication. 3. Fold the rule check into the simplifier. It seems like this folds what is currently quite simple code into the already rather complex simplifier. I'm not entirely sure which of these is the least-evil option. Thoughts? Cheers, - Ben P.S. There is also the matter of cyclic module imports. To address these I've split up `SimplUtils.hs` into `SimplCont.hs` and `SimplInline.hs`. Given these two have no cross-dependencies this seems like a reasonable split even independent of the `RuleFun` rework. `Rules.hs` can then import `SimplCont.hs` (although it needs an hs-boot file to satisfy references in `LoadIface.hs`, `HscTypes.hs`, `MkId.hs`). I'll probably reevaluate the need for hs-boot files later. If anyone sees a better restructuring let me know. [1] https://ghc.haskell.org/trac/ghc/ticket/9661#comment:12 [2] https://github.com/ghc/ghc/compare/ghc-7.10...bgamari:wip/rule-context [3] https://github.com/ghc/ghc/commit/a978a4766ebf692820c3b491522b2dd6c642005f [4] https://github.com/bgamari/ghc/blob/c71fb84b8c9ec9c1e279df8c75ceb8a537801aa…

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GHC with cabal-install
by Kazu Yamamoto 27 Feb '15

27 Feb '15

Hello, To my experience, it is easy to install GHC to Linux such as CentOS. But it is hard to install cabal-install after that. Are there any reasons to not include cabal-install in GHC binary packages? GHC provides Cabal library. Why not cabal-install? --Kazu

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RE: The suggested redundant import solution doesn't work for explicit import lists
by Simon Peyton Jones 26 Feb '15

26 Feb '15

OK. I've created a ticket https://ghc.haskell.org/trac/ghc/ticket/10117 In fact there is a pretty good specification here https://ghc.haskell.org/trac/ghc/wiki/Commentary/Compiler/UnusedImports So back to you: based on the existing, can you think of a variant that would work better? Simon | -----Original Message----- | From: Herbert Valerio Riedel [mailto:hvriedel@gmail.com] | Sent: 24 February 2015 12:00 | To: Simon Peyton Jones | Cc: Herbert Valerio Riedel; Johan Tibell; Edward Kmett; Austin Seipp | Subject: Re: The suggested redundant import solution doesn't work for | explicit import lists | | Simon, | | The problem: | | trying to avoid redundant-import warnings due symbols having moved to | 'Prelude' due to AMP/FTP w/o CPP usage | | e.g. | | import Control.Applicative (Applicative) | | foo :: Applicative f => ... | foo = ... | | now warns that 'Applicative' is redundant, as it's exported from | 'Prelude' now. 'Monoid' is another such example that's now re-exported | from 'Prelude' (but wasn't before GHC 7.10). | | | One thing that happens to work is the trick shown at | https://ghc.haskell.org/trac/ghc/wiki/Migration/7.10#GHCsaysTheimporto | f...isredundant | i.e. | | module Foo (Int, Word, Monoid(..)) where | | import Data.Monoid | import Data.Word | import Prelude | | as in that case, 'Prelude' is explicitly imported last, and so GHC | doesn't warn about Data.{Word,Monoid} being redundant (due to the way | the redundancy-check is implemented in GHC) | | However, if the example above is rewritten as | | module Foo (Int, Word, Monoid(..)) where | | import Data.Monoid (Monoid(..)) | import Data.Word (Word) | import Prelude | | GHC would warn, as it handles import-listed symbols differently than | wildcard imports... | | and the question is, whether we can easily get the latter example to | become warning free as well w/o risking breakages elsewhere... | | ...is it clearer now what I'm suggesting? | | Cheers, | hvr | | On 2015-02-24 at 12:50:35 +0100, Simon Peyton Jones wrote: | > I'm sorry, but can someone re-articulate the question? I'm deep | underwater, so reluctant to reverse-engineer the question from the | thread. | > I think you are asking for some feature. But I'm not sure what the | spec is. | > | > Simon | > | > | -----Original Message----- | > | From: Herbert Valerio Riedel [mailto:hvriedel@gmail.com] | > | Sent: 24 February 2015 11:29 | > | To: Johan Tibell | > | Cc: Edward Kmett; Simon Peyton Jones; Austin Seipp | > | Subject: Re: The suggested redundant import solution doesn't work | > | for explicit import lists | > | | > | Johan, | > | | > | You're right, I'm afraid the Prelude-trick doesn't work well with | > | import-lists... not sure though if it's worth the risk to tweak | GHC | > | 7.10.1's redundant-warning detection to make it work here too... | > | | > | @SPJ, any comments? | > | | > | for more context: | > | | > | - | > | | https://ghc.haskell.org/trac/ghc/wiki/Migration/7.10#GHCsaysTheimporto | f.. | > | .isredundant | > | - | > | | http://www.reddit.com/r/haskell/comments/2wx64g/ghc_710_will_use_pla | > | n_ftp | > | /covdas0 | > | | > | Cheers, | > | hvr | > | | > | On 2015-02-24 at 11:47:30 +0100, Johan Tibell wrote: | > | > The suggested fix for unused imports resulting from the move of | e.g. | > | > Data.Monoid doesn't work when using explicit import lists: | > | > | > | > $ cat Test.hs | > | > module Test where | > | > | > | > import Data.Monoid (Monoid) | > | > import Prelude | > | > | > | > f :: Monoid a => a | > | > f = undefined | > | > $ ghc-7.10.0.20150123 -Wall /tmp/Test.hs | > | > [1 of 1] Compiling Test ( /tmp/Test.hs, /tmp/Test.o | ) | > | > | > | > /tmp/Test.hs:3:1: Warning: | > | > The import of ‘Data.Monoid’ is redundant | > | > except perhaps to import instances from ‘Data.Monoid’ | > | > To import instances alone, use: import Data.Monoid() | > | > | > | > It does work if you don't have an import list (bad idea) or use | > | qualified | > | > imports (good idea). | > | > | > | > -- Johan | > | | > | -- | > | "Elegance is not optional" -- Richard O'Keefe | | -- | "Elegance is not optional" -- Richard O'Keefe

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Broken `cabal haddock --hoogle` with GHC 7.10
by Michael Snoyman 26 Feb '15

26 Feb '15

I'm not really able to follow the details of this, but I wanted to raise to everyone's attention a serious bug with the current GHC 7.10 RC, Cabal 1.22, and/or Haddock. Currently, running `cabal haddock --hoogle` does not work. There seem to be two different issues open about it: https://github.com/haskell/haddock/issues/361 https://github.com/haskell/cabal/issues/2297 I really don't understand the issues here, but I'd claim that the severity of this should probably be a blocker for a GHC 7.10 release.

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Out of action
by Simon Peyton Jones 25 Feb '15

25 Feb '15

Folks Just to say that I'm very silent right now because of the ICFP deadline on Friday. Probably no cycles for GHC until Monday at earliest. Simon

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Re: [Haskell-cafe] PowerPC variants (GHC 7.8.3)
by Carter Schonwald 25 Feb '15

25 Feb '15

Hey Jon, I do know that some of the GHC dev team is probably best equipped to answer your question, i'm cc'ing the ghc dev and users lists so they can jump in and help! -Carter On Wed, Feb 25, 2015 at 7:11 AM, Jon Schneider <haskell(a)jschneider.net> wrote: > Good morning, > > We have a product with an MPC8544E we might want to target. Also known as > PowerQUICC and e500v2. The ABI is gnuspe rather than gnueabi. > > I have built a powerpc---ghc cross compiler but the thing stopping "hello > world" is a SIGILL happening in StgCRun.c where the stfd and lfd > instructions are used to stash registers. The e500 has different > instructions but that cannot be dropped in trivially because of offset > encoding Commenting these out fixes "hello world" though this surely only > scratches the surface of what would need doing. > > I notice that whereas ARMv5, v6 and v7 appear to be catered for along with > various knobs and whistles there appears to be no such thing for PowerPC. > > Is anybody else out there working on this area ? > > Jon > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe >

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EvTerms and how they are used
by Jan Bracker 25 Feb '15

25 Feb '15

Hello, I am trying to use the new type checker plugins [1] that are implemented in head. When successful a plugin has to return a [(EvTerm, Ct)] for the solved constraints. The documentation on EvTerms is scarce [2,3,4] and I could not find papers that explain them (many talk about 'evidence', but they never get concrete). So far I have figured out that "EvDFunApp DFunId [Type] [EvTerm]" selects a certain instance to be used for a constraint, though I don't know what the list of EvTerms in the end is for. I am also a bit unclear on how the "[Type]" is used.If I turn on '-dcore-lint' I get errors. So I still seem to be using it wrong. I have also asked in IRC, but did not get a response to my question. I am sorry if this is the wrong mailing list to ask. If there is a more apropriate place just point it out. Best, Jan [1]: https://ghc.haskell.org/trac/ghc/wiki/Plugins/TypeChecker [2]: http://haskell.inf.elte.hu/docs/7.11.20150225.noWin32/html/libraries/ghc-7.… [3]: http://haskell.inf.elte.hu/docs/7.11.20150225.noWin32/html/libraries/ghc-7.… [4]: http://haskell.inf.elte.hu/docs/7.11.20150225.noWin32/html/users_guide/comp…

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Arrow Development
by Thomas Bereknyei 24 Feb '15

24 Feb '15

I am looking at the proc notation de-sugar and I see results like this when using a Free Arrow (mostly copied from [1]): line2 = proc n -> do Effect getURLSum *** Effect getURLSum -< n Seq [Pure ] (Seq [Pure ] (Seq [Pure ] (Seq [Pure ](Par <Effect > {Effect } ) ) ) ) while this is so much simpler: line2 = Effect getURLSum *** Effect getURLSum Par <Effect > {Effect } Those `Seq [Pure ]` sequences come from application of (.) and I have noticed many similar inefficiencies in the Arrow preprocessor. Eventually the goal would be to optimize when possible, for example I started looking into this in order to use `concurrently` for (***) when in IO. There was a rewrite mentioned here [2]. The deSugar/DsArrows.hs [3] looks convoluted. Any progress or work needed? Or are Arrows not used much and not worth the effort? [1] http://stackoverflow.com/questions/12001350/useful-operations-on-free-arrows [2]https://mail.haskell.org/pipermail/haskell-cafe/2013-August/109795.html [3]https://github.com/ghc/ghc/blob/master/compiler/deSugar/DsArrows.hs -Tom

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