Thanks for the feedback and support.
Alan
On Wed, Oct 1, 2014 at 6:37 PM, Neil Mitchell <ndmitch...@gmail.com> wrote:
> I was getting a bit lost between the idea and the implementation. Let
> me try rephrasing the idea in my own words.
>
> The goal: Capture inner source spans in AST syntax nodes. At the
> moment if ... then ... else ... captures the spans [if [...] then
> [...] else [...]]. We want to capture the spans for each keyword as
> well, so: [{if} [...] {then} [...] {else} [...]].
>
> The proposal: Rather than add anything to the AST, have a separate
> mapping (SrcSpan,AstCtor) to [SrcSpan]. So you give in the SrcSpan
> from the IfThenElse node, and some token for the IfThenElse
> constructor, and get back a list of IfThenElse for the particular
> keyword.
>
> I like the proposal because it adds nothing inside the AST, and
> requires no fresh invariants of the AST. I dislike it because the
> contents of that separate mapping are highly tied up with the AST, and
> easy to get out of sync. I think it's the right choice for three
> reasons, 1) it is easier to try out and doesn't break the AST, so we
> have more scope for changing our minds later; 2) the same technique is
> able to represent things other than SrcSpan without introducing a
> polymorphic src span; 3) the people who pay the complexity are the
> people who use it, which is relatively few people.
>
> That said, as a tweak to the API, rather than a single data type for
> all annotations, you could have:
>
> data AnnIfThenElse = AnnIfThenElse {posIf, posThen, posElse :: SrcSpan}
> data AnnDo = AnnDo {posDo :: SrcSpan}
>
> Then you could just have an opaque Map (SrcSpan, TypeRep) Dynamic,
> with the invariant that the TypeRep in the key matches the Dynamic.
> Then you can have: getAnnotation :: Typeable a => Annotations ->
> SrcSpan -> Maybe a. I think it simplifies some of the TypeRep trickery
> you are engaging in with mkAnnKey.
>
> Thanks, Neil
>
> On Wed, Oct 1, 2014 at 5:06 PM, Simon Peyton Jones
> <simo...@microsoft.com> wrote:
> > Let me urge you, once more, to consult some actual heavy-duty users of
> these
> > proposed facilities. I am very keen to avoid investing design and
> > implementation effort in facilities that may not meet the need.
> >
> >
> >
> > If they end up acclaiming the node-key idea, then we should surely simply
> > make the key an abstract type, simply an instance of Hashable, Ord, etc.
> >
> >
> >
> > Simon
> >
> >
> >
> > From: Alan & Kim Zimmerman [mailto:alan.z...@gmail.com]
> > Sent: 30 September 2014 19:48
> > To: Simon Peyton Jones
> > Cc: Richard Eisenberg; Edward Z. Yang; ghc-devs@haskell.org
> >
> >
> > Subject: Re: Feedback request for #9628 AST Annotations
> >
> >
> >
> > On further reflection of the goals for the annotation, I would like to
> put
> > forward the following proposal for comment
> >
> >
> > Instead of physically placing a "node-key" in each AST Node, a virtual
> > node key can be generated from any `GenLocated SrcSpan e' comprising a
> > combination of the `SrcSpan` value and a unique identifier from the
> > constructor for `e`, perhaps using its `TypeRep`, since the entire AST
> > derives Typeable.
> >
> > To further reduce the intrusiveness, a base Annotation type can be
> > defined that captures the location of noise tokens for each AST
> > constructor. This can then be emitted from the parser, if the
> > appropriate flag is set to enable it.
> >
> > So
> >
> > data ApiAnnKey = AK SrcSpan TypeRep
> >
> > mkApiAnnKey :: (Located e) -> ApiAnnKey
> > mkApiAnnKey = ...
> >
> > data Ann =
> > ....
> > | AnnHsLet SrcSpan -- of the word "let"
> > SrcSpan -- of the word "in"
> >
> > | AnnHsDo SrcSpan -- of the word "do"
> >
> > And then in the parser
> >
> > | 'let' binds 'in' exp { mkAnnHsLet $1 $3 (LL $ HsLet (unLoc
> $2)
> > $4) }
> >
> > The helper is
> >
> > mkAnnHsLet :: Located a -> Located b -> LHsExpr RdrName -> P (LHsExpr
> > RdrName)
> > mkAnnHsLet (L l_let _) (L l_in _) e = do
> > addAnnotation (mkAnnKey e) (AnnHsLet l_let l_in)
> > return e;
> >
> > The Parse Monad would have to accumulate the annotations to be
> > returned at the end, if called with the appropriate flag.
> >
> > There will be some boilerplate in getting the annotations and helper
> > functions defined, but it will not pollute the rest.
> >
> > This technique can also potentially be backported to support older GHC
> > versions via a modification to ghc-parser.
> >
> > https://hackage.haskell.org/package/ghc-parser
> >
> > Regards
> >
> > Alan
> >
> >
> >
> > On Tue, Sep 30, 2014 at 2:04 PM, Alan & Kim Zimmerman <
> alan.z...@gmail.com>
> > wrote:
> >
> > I tend to agree that this change is much too intrusive for what it
> attempts
> > to do.
> >
> > I think the concept of a node key could be workable, and ties in to the
> > approach I am taking in ghc-exactprint [1], which uses a SrcSpan together
> > with node type as the annotation key.
> >
> > [1] https://github.com/alanz/ghc-exactprint
> >
> >
> >
> > On Tue, Sep 30, 2014 at 11:19 AM, Simon Peyton Jones <
> simo...@microsoft.com>
> > wrote:
> >
> > I'm anxious about it being too big a change too.
> >
> > I'd be up for it if we had several "customers" all saying "yes, this is
> > precisely what we need to make our usage of the GHC API far far easier".
> > With enough detail so we can understand their use-case.
> >
> > Otherwise I worry that we might go to a lot of effort to solve the wrong
> > problem; or to build a solution that does not, in the end, work for the
> > actual use-case.
> >
> > Another way to tackle this would be to ensure that syntax tree nodes
> have a
> > "node-key" (a bit like their source location) that clients could use in a
> > finite map, to map node-key to values of their choice.
> >
> > I have not reviewed your patch in detail, but it's uncomfortable that the
> > 'l' parameter gets into IfGblEnv and DsM. That doesn't smell right.
> >
> > Ditto DynFlags/HscEnv, though I think here that you are right that the
> > "hooks" interface is very crucial. After all, the WHOLE POINT is too
> make
> > the client interface more flexible. I would consult Luite and Edsko, who
> > were instrumental in designing the new hooks interface
> > https://ghc.haskell.org/trac/ghc/wiki/Ghc/Hooks
> > (I'm not sure if that page is up to date, but I hope so)
> >
> > A good way to proceed might be to identify some of the big users of the
> GHC
> > API (I'm sure I don't know them all), discuss with them what would help
> > them, and share the results on a wiki page.
> >
> > Simon
> >
> >
> > | -----Original Message-----
> > | From: ghc-devs [mailto:ghc-devs-boun...@haskell.org] On Behalf Of
> > | Richard Eisenberg
> > | Sent: 30 September 2014 03:04
> > | To: Edward Z. Yang
> > | Cc: ghc-devs@haskell.org
> > | Subject: Re: Feedback request for #9628 AST Annotations
> > |
> > | I'm only speaking up because Alan is specifically requesting feedback:
> > | I'm really ambivalent about this. I agree with Edward that this is a
> > | big change and adds permanent noise in a lot of places. But, I also
> > | really respect the goal here -- better tool support. Is it worthwhile
> > | to do this using a dynamically typed bit (using Typeable and such),
> > | which would avoid the noise? Maybe.
> > |
> > | What do other languages do? Do we know what, say, Agda does to get
> > | such tight coupling with an editor? Does, say, Eclipse have such a
> > | chummy relationship with a Java compiler to do its refactoring, or is
> > | that separately implemented? Haskell/GHC is not the first project to
> > | have this problem, and there's plenty of solutions out there. And,
> > | unlike most other times, I don't think Haskell is exceptional in this
> > | regard (there's nothing very special about Haskell's AST, maybe beyond
> > | indentation-awareness), so we can probably adopt other solutions
> > | nicely.
> > |
> > | Richard
> > |
> > | On Sep 29, 2014, at 8:58 PM, "Edward Z. Yang" <ezy...@mit.edu> wrote:
> > |
> > | > Excerpts from Alan & Kim Zimmerman's message of 2014-09-29 13:38:45
> > | -0700:
> > | >> 1. Is this change too big, should I scale it back to just update
> > | the
> > | >> HsSyn structures and then lock it down to Located SrcSpan for all
> > | >> the rest?
> > | >
> > | > I don't claim to speak for the rest of the GHC developers, but I
> > | think
> > | > this change is too big. I am almost tempted to say that we
> > | shouldn't
> > | > add the type parameter at all, and do something else (maybe Backpack
> > | > can let us extend SrcSpan in a modular way, or even use a
> > | dynamically
> > | > typed map for annotations.)
> > | >
> > | > Edward
> > | > _______________________________________________
> > | > ghc-devs mailing list
> > | > ghc-devs@haskell.org
> > | > http://www.haskell.org/mailman/listinfo/ghc-devs
> > |
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> >
> >
> >
> >
> >
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