Reify and separating renamer+TH from type-checking - ghc-devs - Haskell.org

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Reify and separating renamer+TH from type-checking

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Re: FW: Shaking up GHC

Edward Z. Yang

8 Jan 2016 8 Jan '16

2:40 p.m.

I implemented the refactoring to run the renamer and TH splices all first before doing any type-checking, but actually there's a problem: Template Haskell splices can call 'reify', which needs the type information in order to supply the information about the identifiers in question. I can't think of any good way around this problem. Edward

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David Kraeutmann

8 Jan 8 Jan

3:15 p.m.

I think I ran into this issue when we had the Safe Haskell annotation bug, which is why I just disabled annotations for SH. I can't think of a way around it unless we change the TH spec. On 1/8/2016 8:40 PM, Edward Z. Yang wrote:

I implemented the refactoring to run the renamer and TH splices all first before doing any type-checking, but actually there's a problem: Template Haskell splices can call 'reify', which needs the type information in order to supply the information about the identifiers in question. I can't think of any good way around this problem.

Edward _______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs

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Simon Peyton Jones

6:08 p.m.

Bother. That's true. And it's a vital feature. Otherwise how do we do data T = T1 | T2 $(makeLenses 'T) So we can't separate the two after all. Sorry -- I totally forgot about that. Very annoying. Simon | -----Original Message----- | From: Edward Z. Yang [mailto:ezyang@mit.edu] | Sent: 08 January 2016 19:40 | To: Simon Peyton Jones | Cc: ghc-devs | Subject: Reify and separating renamer+TH from type-checking | | I implemented the refactoring to run the renamer and TH splices all | first before doing any type-checking, but actually there's a problem: | Template Haskell splices can call 'reify', which needs the type | information in order to supply the information about the identifiers | in question. I can't think of any good way around this problem. | | Edward

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Jacques Carette

12 Jan 12 Jan

9:57 p.m.

FYI, metaocaml runs into the same problem [for different reasons]. There the design decision was to not allow using a data-type in the same file as its definition. Separate compilation then solves the problem. This is a minor pain. But in Haskell, this would lead to orphan instances when using TH to derive instances, which is likely to be thought of as a rather bigger pain. Jacques On 2016-01-08 6:08 PM, Simon Peyton Jones wrote:

Bother. That's true. And it's a vital feature. Otherwise how do we do

data T = T1 | T2 $(makeLenses 'T)

So we can't separate the two after all. Sorry -- I totally forgot about that. Very annoying.

Simon

| -----Original Message----- | From: Edward Z. Yang [mailto:ezyang@mit.edu] | Sent: 08 January 2016 19:40 | To: Simon Peyton Jones | Cc: ghc-devs | Subject: Reify and separating renamer+TH from type-checking | | I implemented the refactoring to run the renamer and TH splices all | first before doing any type-checking, but actually there's a problem: | Template Haskell splices can call 'reify', which needs the type | information in order to supply the information about the identifiers | in question. I can't think of any good way around this problem. | | Edward _______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs

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Edward Kmett

13 Jan 13 Jan

9:15 a.m.

Worse, 'reify' is in many cases the very reason why folks are using template-haskell in the first place to build instances or classes based on properties of data types above the splice in the current module. On Fri, Jan 8, 2016 at 2:40 PM, Edward Z. Yang wrote:

I implemented the refactoring to run the renamer and TH splices all first before doing any type-checking, but actually there's a problem: Template Haskell splices can call 'reify', which needs the type information in order to supply the information about the identifiers in question. I can't think of any good way around this problem.

Edward _______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs

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participants (5)

David Kraeutmann
Edward Kmett
Edward Z. Yang
Jacques Carette
Simon Peyton Jones