- template-haskell - Haskell.org

RE: [Template-haskell] Dyamic scoping question
by Simon Peyton-Jones 02 Nov '04

02 Nov '04

Here's your program boiled down a bit foo = 3 baz = $(varE ("fo" ++ "o")) Like any Haskell compiler, GHC does dependency analysis, and type-checks in that order. There no way for it to see that 'baz' depends on 'foo', so it may well typecheck the definition of baz before that of foo. I haven't actually run your example, but I bet that's what's happening. "-ddump-rn" would tell you, because it shows the code after dependency analysis. I wonder if others have tripped over this. There is a tension between dynamic scope and dependency analysis (which is required for type checking) that's hard to resolve. For example, you probably want the example to work even if the definition of 'foo' is after that of 'baz'; at least that's the standard Haskell story. I suppose a workaround is to put 'foo' in another module, but it's not nice. Simon | -----Original Message----- | From: template-haskell-bounces(a)haskell.org [mailto:template-haskell-bounces@haskell.org] On | Behalf Of Bryn Keller | Sent: 25 October 2004 19:48 | To: template-haskell(a)haskell.org | Subject: [Template-haskell] Dyamic scoping question | | Hi folks, | | I'm trying to use TH to generate parsers and writers for arbitrary | datatypes. In the end I'd like every part of the declaration and | generation of these functions to be automatic, but at this early stage | I'm just trying to get one aspect of all that to work. So at the moment, | all I want is to generate a function that exercises a parsing | computation I've already defined earlier in the module: | | import Text.ParserCombinators.Parsec | | import Splices | | data SomeType = S Int | | sometype_p = do {string "S"; num <- many1 digit; return $ S (read num)} | | readSomeType = $(reifyDecl SomeType >>= mkLineReader) | | | and in Splices.hs: | | module Splices where | | import Language.Haskell.THSyntax | import Text.ParserCombinators.Parsec (parse) | import Data.Char (toLower) | | modifyName f name = concat [modules, ":", f origName] | where | (modules, (_:origName)) = break (==':') name | | lower = map toLower | | mkLineReader :: Dec -> Q Exp | mkLineReader (DataD _ name _ fields _) = do | let parserName = varE $ modifyName ((++"_p").lower) name | [| | \line -> case parse $(parserName) line line of | Left err -> error (show err) | Right val -> val | |] | | Now, when I try to compile this I get a message like so: | | tcLookup: `sometype_p' is not in scope | In the first argument of `parse', namely `sometype_p' | In the scrutinee of a case expression: | parse sometype_p line'0 line'0 | In the case expression: | case parse sometype_p line'0 line'0 of | Left err'1 -> error (show err'1) | Right val'2 -> val'2 | | When I add -ddump-splices, it prints this in addition: | | \ line'0 | -> case | Text.ParserCombinators.Parsec.Prim.parse Main.sometype_p | line'0 | line'0 | of | Data.Either.Left err'1 -> GHC.Err.error (GHC.Show.show err'1) | Data.Either.Right val'2 -> val'2 | | which tells me that the name sometype_p is getting built correctly, but | it's just not finding the sometype_p that I've already defined. I | thought that varE was the way to capture existing variables of this sort | in Template Haskell, was I mistaken? What is the approved way? Or have I | just missed something crucial? | | Thanks, | | Bryn | _______________________________________________ | template-haskell mailing list | template-haskell(a)haskell.org | http://www.haskell.org/mailman/listinfo/template-haskell

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RE: [Template-haskell] Existentials
by Simon Peyton-Jones 27 Oct '04

27 Oct '04

It's not hard, no. Ian Lynagh is usually kind enough to do the honours! Simon | -----Original Message----- | From: template-haskell-bounces(a)haskell.org [mailto:template-haskell-bounces@haskell.org] On | Behalf Of Keean Schupke | Sent: 26 October 2004 11:19 | To: template-haskell(a)haskell.org | Subject: [Template-haskell] Existentials | | Hi, any chance of support for existential datatypes in | template-haskell... It currently supports local universal | quantification: | | data A = A (forall a . a) | | but not existental: | | data A = forall a . A a | | Is this hard to add? It would be really useful to me if TH | did support existentials... | | Regards, | Keean. | _______________________________________________ | template-haskell mailing list | template-haskell(a)haskell.org | http://www.haskell.org/mailman/listinfo/template-haskell

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RE: [Template-haskell] Pattern reification in Template Haskell
by Simon Peyton-Jones 27 Oct '04

27 Oct '04

Yes, I'm afraid that pattern quotations and splices are very much not implemented. There's a whole raft of design questions which we sort-of answer in that design note, but not terribly satisfactorily. I do have a bunch of things on my TH to-do list. Pattern splices aren't at the top of it, in fact, but name-splicing -- the ability to splice a name in a binding position -- would be very useful. But there was so little reaction to my last few messages to this list that TH has slipped down my priority list. (Currently I'm busy with GADTs.) I'm not sure whether the quietness of the TH list is because (a) TH works so well that there's no need to say anything or (b) no one is using it. Simon | -----Original Message----- | From: template-haskell-bounces(a)haskell.org [mailto:template-haskell-bounces@haskell.org] On | Behalf Of Sean Seefried | Sent: 20 October 2004 02:02 | To: Template Haskell Mailing List | Subject: [Template-haskell] Pattern reification in Template Haskell | | Hi all, | | Just a quick question about pattern reification. | | In Tim Sheard and Simon Peyton Jones' notes on Template Haskell paper | we are told that the following declaration would be valid: | | p1 = [p| (x,y) |] | | And that this is literally equivalent to: | | return (Ptuple [Pvar (mkBndr "x"), Pvar (mkBndr "y")]) | | But when I try it I get told that x and y are not in scope. But isn't | that precisely the point? I'm introducing new scope. | I realise there is still some development to be done on Template | Haskell and I was wondering whether this was just one of the things | still on the todo list or whether I was doing something wrong. | | Cheers, | | Sean | | _______________________________________________ | template-haskell mailing list | template-haskell(a)haskell.org | http://www.haskell.org/mailman/listinfo/template-haskell

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Existentials
by Keean Schupke 26 Oct '04

26 Oct '04

Hi, any chance of support for existential datatypes in template-haskell... It currently supports local universal quantification: data A = A (forall a . a) but not existental: data A = forall a . A a Is this hard to add? It would be really useful to me if TH did support existentials... Regards, Keean.

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Dyamic scoping question
by Bryn Keller 26 Oct '04

26 Oct '04

Hi folks, I'm trying to use TH to generate parsers and writers for arbitrary datatypes. In the end I'd like every part of the declaration and generation of these functions to be automatic, but at this early stage I'm just trying to get one aspect of all that to work. So at the moment, all I want is to generate a function that exercises a parsing computation I've already defined earlier in the module: import Text.ParserCombinators.Parsec import Splices data SomeType = S Int sometype_p = do {string "S"; num <- many1 digit; return $ S (read num)} readSomeType = $(reifyDecl SomeType >>= mkLineReader) and in Splices.hs: module Splices where import Language.Haskell.THSyntax import Text.ParserCombinators.Parsec (parse) import Data.Char (toLower) modifyName f name = concat [modules, ":", f origName] where (modules, (_:origName)) = break (==':') name lower = map toLower mkLineReader :: Dec -> Q Exp mkLineReader (DataD _ name _ fields _) = do let parserName = varE $ modifyName ((++"_p").lower) name [| \line -> case parse $(parserName) line line of Left err -> error (show err) Right val -> val |] Now, when I try to compile this I get a message like so: tcLookup: `sometype_p' is not in scope In the first argument of `parse', namely `sometype_p' In the scrutinee of a case expression: parse sometype_p line'0 line'0 In the case expression: case parse sometype_p line'0 line'0 of Left err'1 -> error (show err'1) Right val'2 -> val'2 When I add -ddump-splices, it prints this in addition: \ line'0 -> case Text.ParserCombinators.Parsec.Prim.parse Main.sometype_p line'0 line'0 of Data.Either.Left err'1 -> GHC.Err.error (GHC.Show.show err'1) Data.Either.Right val'2 -> val'2 which tells me that the name sometype_p is getting built correctly, but it's just not finding the sometype_p that I've already defined. I thought that varE was the way to capture existing variables of this sort in Template Haskell, was I mistaken? What is the approved way? Or have I just missed something crucial? Thanks, Bryn

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Pattern reification in Template Haskell
by Sean Seefried 20 Oct '04

20 Oct '04

Hi all, Just a quick question about pattern reification. In Tim Sheard and Simon Peyton Jones' notes on Template Haskell paper we are told that the following declaration would be valid: p1 = [p| (x,y) |] And that this is literally equivalent to: return (Ptuple [Pvar (mkBndr "x"), Pvar (mkBndr "y")]) But when I try it I get told that x and y are not in scope. But isn't that precisely the point? I'm introducing new scope. I realise there is still some development to be done on Template Haskell and I was wondering whether this was just one of the things still on the todo list or whether I was doing something wrong. Cheers, Sean

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Call for participation: GPCE'04 -- Generative Programming and Component Engineering
by Eelco Visser 26 Aug '04

26 Aug '04

CALL FOR PARTICIPATION ---------------------------------------------------------------------- Third International Conference on Generative Programming and Component Engineering (GPCE'04) Vancouver, October 24-28, 2004 co-located with OOPSLA 2004 and ISMM 2004 http://gpce04.gpce.org ---------------------------------------------------------------------- Online Registration http://www.regmaster.com/oopsla2004.html early registration with reduced rates closes September 16 ---------------------------------------------------------------------- Generative and component approaches have the potential to revolutionize software development in a similar way as automation and components revolutionized manufacturing. Generative Programming (developing programs that synthesize other programs), Component Engineering (raising the level of modularization and analysis in application design), and Domain-Specific Languages (elevating program specifications to compact domain-specific notations that are easier to write and maintain) are key technologies for automating program development. GPCE arose as a joint conference, merging the prior conference on Generative and Component-Based Software Engineering (GCSE) and the Workshop on Semantics, Applications, and Implementation of Program Generation (SAIG). The goal of GPCE is to provide a meeting place for researchers and practitioners interested in cutting edge approaches to software development. We aim to foster further cross-fertilization between the software engineering research community on the one hand, and the programming languages community on the other, in addition to supporting the original research goals of both the GCSE and the SAIG communities. We seek papers both in software engineering and in programming languages, and especially those that bridge the gap and are accessible to both communities at the same time. * Invited speakers * Keynote: Jack Greenfield on Software Factories * Peter Mosses on Modular Language Descriptions * Technical program * 25 papers * Aspect-orientation * Staged programming * Meta-programming * Model-driven approaches * Product lines * Domain-specific languages * Tutorials * Adaptive Object-Model Architecture: Dynamically Adapting to Changing Requirements * Multi-stage Programming in Meta-OCaml * Generative Software Development * Program Transformation Systems: Theory and Practice for Software Generation, Maintenance and Reengineering * Workshops * Software Transformation Systems Workshop * First MetaOCaml Workshop * Young Researchers Workshop * Workshop on Best Practices Model-Driven Software Development * Workshop on Managing Variabilities Consistently in Design and Code * Demonstrations * Implementation of DSLs using staged interpreters in MetaOCaml * MetaEdit+: Domain-Specific Modeling for Full Code Generation Demonstrated * Towards Domain-Driven Development: the SmartTools Software Factory * Xirc: Cross-Artifact Information Retrieval * C-SAW and GenAWeave: A Two-Level Aspect Weaving Toolsuite * The Concern Manipulation Environment * Program Transformations for Re-Engineering C++ Components

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FW: [Template-haskell] FW: [ ghc-Bugs-992200 ] Template crash onconstructing existential datatype
by Simon Peyton-Jones 21 Aug '04

21 Aug '04

...and the third one... -----Original Message----- From: template-haskell-bounces(a)haskell.org [mailto:template-haskell-bounces@haskell.org] On Behalf Of Simon Peyton-Jones Sent: 19 July 2004 17:35 To: template-haskell(a)haskell.org Subject: [Template-haskell] FW: [ ghc-Bugs-992200 ] Template crash onconstructing existential datatype Dear Template Haskell folk This SourceForge bug is another example of the bad things that happen when: - a TH program constructs a syntactically invalid program - and then splices it in The trouble is that Convert.convertToHsExpr :: TH.Exp -> LHsExpr RdrName is a pure function, and fails "hard" with a panic, whereas it should really be in the TcM monad, and fail in the way any other type error fails. It's a user error, and should not show up as a panic. Would anyone like to fix hsSyn/Convert.lhs so that it lives in the Tc monad? The call (in TcSplice) is easily changed. It'd probably make sense to move it from hsSyn/ to typecheck/ I'm thinking about putting types in the syntax tree, so if others can help out with tidying up like this, it'd be great. Simon -----Original Message----- From: glasgow-haskell-bugs-bounces(a)haskell.org [mailto:glasgow-haskell-bugs-bounces@haskell.org] On Behalf Of SourceForge.net Sent: 16 July 2004 10:11 To: noreply(a)sourceforge.net Subject: [ ghc-Bugs-992200 ] Template crash on constructing existential datatype Bugs item #992200, was opened at 2004-07-16 09:11 Message generated for change (Tracker Item Submitted) made by Item Submitter You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=108032&aid=992200&grou p_id=8032 Category: Compiler Group: 6.2.1 Status: Open Resolution: None Priority: 5 Submitted By: Mike Aizatsky (mm_aa) Assigned to: Nobody/Anonymous (nobody) Summary: Template crash on constructing existential data type Initial Comment: Windows XP D:\Tools\ghc>ghc-6.2.1\bin\ghc.exe -fglasgow-exts --make foo.hs Chasing modules from: foo.hs Compiling Any ( ./Any.hs, ./Any.o ) Compiling Foo ( foo.hs, foo.o ) Loading package base ... linking ... done. Loading package haskell98 ... linking ... done. Loading package haskell-src ... linking ... done. ghc.exe: panic! (the `impossible' happened, GHC version 6.2.1): Malformed predicate module Any where import Language.Haskell.THSyntax genAny :: DecQ -> Q [Dec] genAny decl = do{ d <- decl ; case d of ClassD _ name _ decls -> sequenceQ [genAnyClass (name) decls] _ -> error "genAny can be applied to classes only" } genAnyClass :: String -> [Dec] -> DecQ genAnyClass name decls = do{ returnQ (DataD [forall] anyName [] [constructor] []) } where anyName = "Any" ++ name ++ "1111" constructor = NormalC anyName [(NotStrict, VarT "a")] forall = ForallT [] [] (VarT "a") module Foo where import Any class MyInterface a where foo :: a -> Int foo1 :: Int -> a -> Int $(genAny (reifyDecl MyInterface)) ---------------------------------------------------------------------- You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=108032&aid=992200&grou p_id=8032 _______________________________________________ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs(a)haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs _______________________________________________ template-haskell mailing list template-haskell(a)haskell.org http://www.haskell.org/mailman/listinfo/template-haskell

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FW: [Template-haskell] FW: [ ghc-Bugs-992199 ] Template crash onexistential types
by Simon Peyton-Jones 21 Aug '04

21 Aug '04

Second message referred to in my last post... -----Original Message----- From: template-haskell-bounces(a)haskell.org [mailto:template-haskell-bounces@haskell.org] On Behalf Of Simon Peyton-Jones Sent: 19 July 2004 17:51 To: template-haskell(a)haskell.org Subject: [Template-haskell] FW: [ ghc-Bugs-992199 ] Template crash onexistential types My previous message was about robust-ifying the conversion from: TH.Syntax -> HsSyn but the other direction has very similar problems. The functions in DsMeta convert: HsSyn -> TH.Syntax Unfortunately, of course TH does not implement all of GHC's extensions, so the desugaring can fall over badly. The right thing to do is presumably to make the desugarer monad support failure and errors, like the type checker monad does, and fail more gracefully. Again, is there anyone who'd be prepared to take this on? Simon -----Original Message----- From: glasgow-haskell-bugs-bounces(a)haskell.org [mailto:glasgow-haskell-bugs-bounces@haskell.org] On Behalf Of SourceForge.net Sent: 16 July 2004 10:10 To: noreply(a)sourceforge.net Subject: [ ghc-Bugs-992199 ] Template crash on existential types Bugs item #992199, was opened at 2004-07-16 09:08 Message generated for change (Settings changed) made by mm_aa You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=108032&aid=992199&grou p_id=8032 Category: Compiler Group: 6.2.1 Status: Open Resolution: None Priority: 5 Submitted By: Mike Aizatsky (mm_aa) Assigned to: Nobody/Anonymous (nobody) >Summary: Template crash on existential types Initial Comment: Windows XP D:\Tools\ghc>ghc-6.2.1\bin\ghc.exe -fglasgow-exts foo.hs ghc.exe: panic! (the `impossible' happened, GHC version 6.2.1): deSugar/DsMeta.hs:286: Non-exhaustive patterns in function repC module Foo where import Language.Haskell.THSyntax class MyInterface a where foo :: a -> Int data AnyMyInterface = forall a. (MyInterface a) => AnyMyInterface a test = do{ d <- unQ(reifyDecl AnyMyInterface) ; print d } ---------------------------------------------------------------------- You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=108032&aid=992199&grou p_id=8032 _______________________________________________ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs(a)haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs _______________________________________________ template-haskell mailing list template-haskell(a)haskell.org http://www.haskell.org/mailman/listinfo/template-haskell

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RE: [Template-haskell] instance of Lift for Exp
by Simon Peyton-Jones 21 Jul '04

21 Jul '04

| While on the topic of TH, let me float "yet another idea"TM | Include {-# #-} pragmas in the TH abstract syntax. | | Why? Because it would allow domain/library-specific hints and | annotations. | | data Pragma = PragmaGhcRule ... | PragmaGhcSpecialise ... | PragmaOther String --free form | | My application of this might be to let the user indicate binding times | when doing partial evaluation, eg: | | {-# BT foo :: Static -> Dynamic -> Dynamic #-} | foo :: Int -> Int -> int | foo x y = ... Reasonable idea. I'll put it in the list, but if anyone wants to have a go at implementing it, go right ahead. Simon

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