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RE: Type checking expressions
by Simon Peyton Jones 05 Mar '18

05 Mar '18

Always cc ghc-devs! Bottle-necking on me may well yield a slow response! Or even Haskell-café. What is the type of (\x -> [x,y])? Where y is in scope with type y::a. Presumably something like a -> [a]? Or is it forall a. a -> [a]? And would your answer change if you had just (\x -> [x,x])? Generalisation is tricky, and for terms with non-closed types it is hard to know what you need in your use-case. A type like ‘a’ might be a very fine answer! A lot depends on precisely what you are trying to do. Simon From: Peter Podlovics [mailto:peter.d.podlovics@gmail.com] Sent: 05 March 2018 14:54 To: Simon Peyton Jones <simonpj(a)microsoft.com> Subject: Re: Type checking expressions My main concern with that approach is that it might not give the correct type. For example the hsPatType function only gives unconstrained types, so it is incorrect for any numeric literal, since it gives "a" instead of "Num a => a". So the question is whether it is possible to retrieve the context of the type variables as well. Also this problem may arise in the case of expressions as well, that is why I scrapped that approach and tried to type check the AST with the TcM monad directly, but without any success. Could you give me any leads on how to solve this problem? Thanks in advance, Peter On Mon, Mar 5, 2018 at 9:44 AM, Simon Peyton Jones <simonpj(a)microsoft.com<mailto:simonpj@microsoft.com>> wrote: Peter My goal is to determine the type of every expression, pattern etc. in the syntax tree After type checking is complete, the syntax tree is liberally annotated with types. We do not yet have a function hsExprType :: HsExpr Id -> Type but we do have TcHsTyn.hsPatType :: Pat GhcTc -> Type and you or someone could readily make an equivalent for HsExpr. Most type errors are reported by adding an error constraint, but still returning an annotated tree. Some, I’m afraid, are still done in the old way, by throwing an exception – so you don’t get back an annotated tree in that case. But they are relatively rare. Others must have wanted something like this… Simon From: ghc-devs [mailto:ghc-devs-bounces@haskell.org<mailto:ghc-devs-bounces@haskell.org>] On Behalf Of Peter Podlovics Sent: 02 March 2018 12:05 To: ghc-devs(a)haskell.org<mailto:ghc-devs@haskell.org> Subject: Fwd: Type checking expressions Hello everyone, I would like to ask for some advice regarding the type checker part of GHC. My goal is to determine the type of every expression, pattern etc. in the syntax tree. Currently the compiler doesn't store this information, so I have to type check manually. One important aspect is that the program may be ill-typed, but I still want to extract as much information as possible. I tried using local type checking functions (eg.: tcInferSigma), but whenever I used it on an expression that had some "out-of-scope" names in it, it failed. > f xs = length xs The reason was that xs was not in the local environment. My question is: how could I provide the necessary local environment for these type checking functions? Also in the general case, is it possible to somehow annotate each expression with its type during the type checking? The motivation for this is that I want to implement a tool that automatically corrects ill-typed programs based heuristics. For that I need to know the types of certain AST nodes. Peter Podlovics

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Perf for T5837
by Simon Peyton Jones 05 Mar '18

05 Mar '18

Ben Why did you revert this? commit 2756117bd26c2cb70d3f51954a88b7d7bdf3d3f2 Author: Ben Gamari <ben(a)smart-cactus.org> Date: Thu Mar 1 14:06:04 2018 -0500 Revert "Better stats for T5837" This reverts commit d675a354e8db67d87d1f257c3d1d2bf2d58c2b3f. - (wordsize(64), 55813608, 7)]) + (wordsize(64), 51294232, 7)]) It's consistently 8% better for me, but I guess not for you. Does anyone else find this? Simon

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ghcpkg05
by Simon Peyton Jones 05 Mar '18

05 Mar '18

ghcpkg05 is failing on my Linux box. Any ideas? This is a clean build. Simon =====> ghcpkg05(normal) 1 of 1 [0, 0, 0] cd "./ghcpkg05.run" && $MAKE -s --no-print-directory ghcpkg05 Actual stderr output differs from expected: diff -uw "./ghcpkg05.run/ghcpkg05.stderr.normalised" "./ghcpkg05.run/ghcpkg05.run.stderr.normalised" --- ./ghcpkg05.run/ghcpkg05.stderr.normalised 2018-03-05 12:02:14.828489599 +0000 +++ ./ghcpkg05.run/ghcpkg05.run.stderr.normalised 2018-03-05 12:02:14.828489599 +0000 @@ -10,6 +10,13 @@ cannot find any of ["C/D.hi","C/D.p_hi","C/D.dyn_hi"] cannot find any of ["C/E.hi","C/E.p_hi","C/E.dyn_hi"] cannot find any of ["libtestpkg-2.0-XXX.a","libtestpkg-2.0-XXX.p_a","libtestpkg-2.0-XXX-ghc<VERSION>.so","libtestpkg-2.0-XXX-ghc<VERSION>.dylib","testpkg-2.0-XXX-ghc<VERSION>.dll"] on library path +Warning: include-dirs: /5playpen/simonpj/HEAD-1/compiler/stage2/build/utils doesn't exist or isn't a directory +Warning: include-dirs: /5playpen/simonpj/HEAD-1/compiler/stage2/build/../rts/dist/build doesn't exist or isn't a directory +Warning: include-dirs: /5playpen/simonpj/HEAD-1/compiler/stage2/build/stage2 doesn't exist or isn't a directory +Warning: include-dirs: /5playpen/simonpj/HEAD-1/libraries/haskeline/dist-install/build/includes doesn't exist or isn't a directory +Warning: include-dirs: /5playpen/simonpj/HEAD-1/libraries/text/dist-install/build/include doesn't exist or isn't a directory +Warning: include-dirs: /5playpen/simonpj/HEAD-1/libraries/containers/dist-install/build/include doesn't exist or isn't a directory +Warning: include-dirs: /5playpen/simonpj/HEAD-1/libraries/bytestring/dist-install/build/include doesn't exist or isn't a directory The following packages are broken, either because they have a problem listed above, or because they depend on a broken package. *** unexpected failure for ghcpkg05(normal) Unexpected results from: TEST="ghcpkg05" SUMMARY for test run started at Mon Mar 5 12:02:14 2018 GMT 0:00:01 spent to go through 1 total tests, which gave rise to 1 test cases, of which 0 were skipped 0 had missing libraries 0 expected passes 0 expected failures 0 caused framework failures 0 caused framework warnings 0 unexpected passes 1 unexpected failures 0 unexpected stat failures Unexpected failures: ghcpkg05.run ghcpkg05 [bad stderr] (normal)

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RE: tigetnum etc -- help!
by Simon Peyton Jones 05 Mar '18

05 Mar '18

| just to check the obvious, have you made sure to `git submodule | update` everything? have you properly cleaned your build-tree? Thanks. I did clean; and I usually obsessively do git submodule update, but I may have forgotten this time. I think for cabal and hsc2hs. Trying again now... Simon | -----Original Message----- | From: Herbert Valerio Riedel [mailto:hvriedel@gmail.com] | Sent: 05 March 2018 10:55 | To: Simon Peyton Jones <simonpj(a)microsoft.com> | Subject: Re: tigetnum etc -- help! | | Hi Simon, | | just to check the obvious, have you made sure to `git submodule | update` everything? have you properly cleaned your build-tree? | | -- hvr

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tigetnum etc -- help!
by Simon Peyton Jones 05 Mar '18

05 Mar '18

My stage-1 build (from clean) has started failing thus (on Linux). Any ideas? It's pretty disabling because I can't build GHC any more. Simon make ===--- building phase 0 make --no-print-directory -f ghc.mk phase=0 phase_0_builds make[1]: Nothing to be done for 'phase_0_builds'. ===--- building phase 1 make --no-print-directory -f ghc.mk phase=1 phase_1_builds "/usr/local/bin/ghc" -o utils/ghc-pkg/dist/build/tmp/ghc-pkg -hisuf hi -osuf o -hcsuf hc -static -O0 -H64m -Wall -package-db libraries/bootstrapping.conf -hide-all-packages -i -iutils/ghc-pkg/. -iutils/ghc-pkg/dist/build -Iutils/ghc-pkg/dist/build -iutils/ghc-pkg/dist/build/ghc-pkg/autogen -Iutils/ghc-pkg/dist/build/ghc-pkg/autogen -optP-DWITH_TERMINFO -optP-include -optPutils/ghc-pkg/dist/build/ghc-pkg/autogen/cabal_macros.h -package-id Cabal-2.1.0.0 -package-id base-4.10.0.0 -package-id binary-0.8.5.1 -package-id bytestring-0.10.8.2 -package-id containers-0.5.10.2 -package-id directory-1.3.0.2 -package-id filepath-1.4.1.2 -package-id ghc-boot-8.5 -package-id process-1.6.1.0 -package-id terminfo-0.4.1.1 -package-id unix-2.7.2.2 -XHaskell2010 -no-user-package-db -rtsopts -odir utils/ghc-pkg/dist/build -hidir utils/ghc-pkg/dist/build -stubdir utils/ghc-pkg/dist/build -static -O0 -H64m -Wall -package-db libraries/bootstrapping.conf -hide-all-packages -i -iutils/ghc-pkg/. -iutils/ghc-pkg/dist/build -Iutils/ghc-pkg/dist/build -iutils/ghc-pkg/dist/build/ghc-pkg/autogen -Iutils/ghc-pkg/dist/build/ghc-pkg/autogen -optP-DWITH_TERMINFO -optP-include -optPutils/ghc-pkg/dist/build/ghc-pkg/autogen/cabal_macros.h -package-id Cabal-2.1.0.0 -package-id base-4.10.0.0 -package-id binary-0.8.5.1 -package-id bytestring-0.10.8.2 -package-id containers-0.5.10.2 -package-id directory-1.3.0.2 -package-id filepath-1.4.1.2 -package-id ghc-boot-8.5 -package-id process-1.6.1.0 -package-id terminfo-0.4.1.1 -package-id unix-2.7.2.2 -XHaskell2010 -no-user-package-db -rtsopts utils/ghc-pkg/dist/build/Main.o utils/ghc-pkg/dist/build/Version.o /5playpen/simonpj/HEAD-1/libraries/terminfo/dist-boot/build/libHSterminfo-0.4.1.1.a(Base.o):r6De_info: error: undefined reference to 'tigetnum' /5playpen/simonpj/HEAD-1/libraries/terminfo/dist-boot/build/libHSterminfo-0.4.1.1.a(Base.o):r6Df_info: error: undefined reference to 'tigetflag' /5playpen/simonpj/HEAD-1/libraries/terminfo/dist-boot/build/libHSterminfo-0.4.1.1.a(Base.o):r6Dg_info: error: undefined reference to 'tigetstr' /5playpen/simonpj/HEAD-1/libraries/terminfo/dist-boot/build/libHSterminfo-0.4.1.1.a(Base.o):s6Gn_info: error: undefined reference to 'set_curterm' /5playpen/simonpj/HEAD-1/libraries/terminfo/dist-boot/build/libHSterminfo-0.4.1.1.a(Base.o):s6Gb_info: error: undefined reference to 'set_curterm' /5playpen/simonpj/HEAD-1/libraries/terminfo/dist-boot/build/libHSterminfo-0.4.1.1.a(Base.o):s6I7_info: error: undefined reference to 'tparm' /5playpen/simonpj/HEAD-1/libraries/terminfo/dist-boot/build/libHSterminfo-0.4.1.1.a(Base.o):s6JP_info: error: undefined reference to 'set_curterm' /5playpen/simonpj/HEAD-1/libraries/terminfo/dist-boot/build/libHSterminfo-0.4.1.1.a(Base.o):s6JA_info: error: undefined reference to 'setupterm' /5playpen/simonpj/HEAD-1/libraries/terminfo/dist-boot/build/libHSterminfo-0.4.1.1.a(Base.o):s6Jn_info: error: undefined reference to 'set_curterm' /5playpen/simonpj/HEAD-1/libraries/terminfo/dist-boot/build/libHSterminfo-0.4.1.1.a(Base.o):s6KR_info: error: undefined reference to 'tputs' /5playpen/simonpj/HEAD-1/libraries/terminfo/dist-boot/build/libHSterminfo-0.4.1.1.a(Base.o)(.data+0xdc8): error: undefined reference to 'del_curterm' collect2: error: ld returned 1 exit status `gcc' failed in phase `Linker'. (Exit code: 1) utils/ghc-pkg/ghc.mk:70: recipe for target 'utils/ghc-pkg/dist/build/tmp/ghc-pkg' failed make[1]: *** [utils/ghc-pkg/dist/build/tmp/ghc-pkg] Error 1 Makefile:122: recipe for target 'all' failed make: *** [all] Error 2 simonpj@cam-05-unx:~/5builds/HEAD-1$

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Fwd: Type checking expressions
by Peter Podlovics 05 Mar '18

05 Mar '18

Hello everyone, I would like to ask for some advice regarding the type checker part of GHC. My goal is to determine the type of every expression, pattern etc. in the syntax tree. Currently the compiler doesn't store this information, so I have to type check manually. One important aspect is that the program may be ill-typed, but I still want to extract as much information as possible. I tried using local type checking functions (eg.: tcInferSigma), but whenever I used it on an expression that had some "out-of-scope" names in it, it failed. > f xs = length xs The reason was that xs was not in the local environment. My question is: how could I provide the necessary local environment for these type checking functions? Also in the general case, is it possible to somehow annotate each expression with its type during the type checking? The motivation for this is that I want to implement a tool that automatically corrects ill-typed programs based heuristics. For that I need to know the types of certain AST nodes. Peter Podlovics

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Someone please delete my Trac report
by Simon Jakobi 03 Mar '18

03 Mar '18

Hi! Could someone with the appropriate permissions please delete report #26 "Interesting" at https://ghc.haskell.org/trac/ghc/report? When I saved my query I didn't expect that it would be visible to everyone. Cheers, Simon

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Guarded Impredicativity implementation
by Artem Pelenitsyn 02 Mar '18

02 Mar '18

Dear ghc-devs, Is there any work has been done on the latest (ttbomk) proposal for impredicative types in Haskell: > Guarded impredicative polymorphism by Alejandro Serrano, Jurriaan Hage, Dimitrios Vytiniotis, Simon Peyton Jones https://www.microsoft.com/en-us/research/wp-content/uploads/2017/07/impredi… Or are there any plans to do so? I wasn't able to spot any mentions of this in either of GHC's forums (this list, Trac, wiki, ghc-proposals repo). -- Best wishes, Artem Pelenitsyn

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An idea for a different style of metaprogramming evaluation using the optimiser
by Matthew Pickering 28 Feb '18

28 Feb '18

I've had an idea for a while of a different way we could evaluate TH-like splices which would be more lightweight and easier to work with. The idea is to create a third quotation/splicing mechanism which has no introspection (like MetaML) but then to evaluate these quotes and splices in the optimiser rather than using the bytecode interpreter. I am motivated by the many examples of recursive functions in libraries, which when given a statically known argument should be able to be unrolled to produce much better code. It is understandable that the compiler doesn't try to do this itself but there should be an easy way for the user to direct the compiler to do so. (See also https://www.reddit.com/r/haskell/comments/7yvb43/ghc_compiletime_evaluation/) An example to be concrete: Take the power function such that power k n computes k^n. power :: Int -> Int -> Int power k n = if n == 0 then 1 else k * power k (n - 1) If we statically know n then we can create a staged version. We use R to indicate that an argument is dynamically known. power :: R Int -> Int -> R Int power k n = if n == 0 then .< 1 >. else .< ~k * ~(power k (n-1)) >. One way to implement this in Haskell is to use typed template haskell quoting and splicing. The key thing to notice about why this works is that in order to splice `power k (n-1)` we need to evaluate `power k (n-1)` so that we have something of type `R Int` which we can then splice back into the quote. The way this is currently implemented is that the bytecode interpreter runs these splices in order to find out what they evaluate to. The idea is that instead, we add another mode which runs splices in the core-to-core optimiser. The optimiser performs evaluation by beta reduction, inlining and constant folding. For simple definitions on algebraic data types it does a very good job of eliminating overhead. As long as the call is not recursive. If we can just get the optimiser to inline recursive calls in a controlled manner as well, it should do a good job on the unrolled definition. The benefits of this are that it works across all platforms and fits nicely already into the compilation pipeline. It also fits in nicely with the intuition that a "quote" means to stop evaluating and a "splice" means to evaluate. A disadvantage is that the optimiser is only a *partial* evaluator rather than an evaluator. It gets stuck evaluating things containing primitives and so on. I don't forsee this as a major issue but a limitation that library authors should be aware of when writing their staged programs. To go back to the power example, the recursive condition would have to be an inductively defined natural (data N = Z | S N) rather than an Int as the comparison operator for integers can't be evaluated by the optimiser. It is already rather easy to write staged programs which loop if you don't carefully consider the staging so this seems now worse than the status quo. Does this sound at all sensible to anyone else? Matt

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Help with build ordering issue
by Sylvain Henry 26 Feb '18

26 Feb '18

Hi, @Bodigrim is working on a patch (https://phabricator.haskell.org/D4212) to fix #14170. The build fails because of interface file errors: "bad interface file" for GHC.Natural and "failed to load interface" for GHC.Types. I suspect it is a wired-in module build ordering issue but I haven't been able to help fixing it. If anyone with more insights could help it would be much appreciated! Thanks, Sylvain

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