- Glasgow-haskell-users

Pragmas in Lexer
by JP Moresmau 29 Dec '12

29 Dec '12

Hello, I'm using the GHC lexer to parse some haskell code containing a language pragma, in GHC 7.4.2 module Main where import GHC import GHC.Paths ( libdir ) import Lexer import qualified MonadUtils as GMU import StringBuffer import FastString (mkFastString) import SrcLoc import ErrUtils (mkPlainErrMsg) main::IO() main = do let contents="{-# LANGUAGE CPP #-}\nmodule Main where\nmain=undefined" runGhc (Just libdir) $ do flg <- getSessionDynFlags let sb=stringToStringBuffer contents let lexLoc = mkRealSrcLoc (mkFastString "<interactive>") 1 1 let prTS = lexTokenStream sb lexLoc flg case prTS of POk _ toks -> GMU.liftIO $ print $ map (show . unLoc) toks PFailed l msg -> GMU.liftIO $ print $ mkPlainErrMsg l msg This prints: ["ITblockComment \" CPP #\"","ITmodule","ITconid \"Main\"","ITwhere","ITvocurly","ITvarid \"main\"","ITequal","ITvarid \"undefined\""] Why is the first token ITblockComment and not ITlanguage_prag? Do I need to enable something special to get pragma tokens? Thanks! -- JP Moresmau http://jpmoresmau.blogspot.com/

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Updating commentary about PrimOps and codegen
by Jan Stolarek 23 Dec '12

23 Dec '12

Hi all, I've been reading Commentary about PrimOps and code generation and I noticed that it is partially outdated (e.g. references to old code gen files: compiler/codeGen/CgPrimOp.hs): http://hackage.haskell.org/trac/ghc/wiki/Commentary/PrimOps http://hackage.haskell.org/trac/ghc/wiki/Commentary/Compiler/CodeGen Would anyone be so kind to update these pages and possibly other pages about code generation, STG, Cmm and related stuff? I've been trying to figure out how to add new PrimOps and having up to date documentation would be most helpful. Janek

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Separating build tree from the source tree
by Jan Stolarek 21 Dec '12

21 Dec '12

Dear list, I have a GHC source tree in ghc-working. I would like to have a separate build tree in ghc-build, so I did something like this: mkdir ghc-build cd ghc-build lndir ../ghc-working Now, I have two different machines. On openSUSE with git 1.8.0 I get something like this: [killy@xerxes : /dane/uczelnia/projekty/ghc-build] ./configure checking for gfind... no checking for find... /usr/bin/find checking for GHC version date... configure: WARNING: cannot determine snapshot version: no .git or _darcs directory and no VERSION file Despite the warning configure succeeds. On Debian Squeeze with git 1.7.10 the same thing doesn't work: [killy@GLaDOS : /dane/uczelnia/projekty/ghc-build] ./configure checking for gfind... no checking for find... /usr/bin/find checking for GHC version date... fatal: Not a git repository (or any of the parent directories): .git configure: error: failed to detect version date: check that git is in your path Does anyone have a clue why this happens? There are probably some differences on these systems with the most obvious one being git version. On both systems however git doesn't recognize ghc-build as a valid git repository ('git status' failes), but on one of them this is only a warning while on another this is an error. Any advice will be appreciated. Janek

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Tagging subjects of emails sent from the list
by Jan Stolarek 20 Dec '12

20 Dec '12

Would it be possible to change mailing list settings so that topics of emails begin with "[glasgow-haskell-users]" (and for upcoming lists: "[ghc-devs]", "[ghc-commits]" and so on. No quotation marks of course). It would make filtering and searching in the mailbox easier. Janek

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SpecConstr and GADTs
by Nicolas Frisby 19 Dec '12

19 Dec '12

I suspect I've found a situation where, to a first approximation, I'd like SpecConstr to run more than once. I'm specializing on GADT constructors that contain coercions, so the constructor-specialized functions have RHSs with refined types. In my situation, those refined types enable simplifications/specializations that eventually result in additional calls that would lead to further constructor-specializations if the eventual calls were somehow already manifest. But it seems that the simplification/specialization only happens after the SpecConstr pass, so the resulting usages don't lead to further constructor-specialized functions. Ticket 2642 http://hackage.haskell.org/trac/ghc/ticket/2642 is the only mention I've seen of the SpecConstr pass being repeated. The more I think about my desired behavior of SpecConstr, the more I suspect that a failure to maximally share the constructor-specializations (leading to possible non-termination) might be a concern if the pass were simply repeated in my particular case. Regarding broader impact, I suspect this situation might arise with heavy uses of single types. Is there any known mechanisms to handle this interaction between SpecConstr and GADTs? I'll be able to provide concrete details about my situation in a few weeks, if anyone is interested. Thanks for your time.

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How to start with GHC development?
by Jan Stolarek 19 Dec '12

19 Dec '12

Dear list, I'm reposting my message from Haskell-cafe here since this seems like a more appropriate place to ask this question. I would like to learn about internals of GHC and contribute to its development in the future. I read a couple of papers that give a very general overview of GHC (chapter from AoS, papers about inliner and multicore support) and I'm thinking what direction should I pursue now. I got the GHC sources and started reading commentary on the wiki, but it seems that entry barrier is very high. Aside from the problem of understanding the whole project organization itself, I also don't have background on implementation of functional languages. In fact I have a rather basic knowledge of compilers in general - I only took Stanford's online course on Compilers at Coursera. I was thinking that perhaps I should read SPJs "Implementing Functional Languages: a tutorial" or "The Implementation Of Functional Languages" book to learn more about theory? On the other hand I don't know if getting stuck in theory for next couple of months is a good idea. I would greatly appreciate any advice and help. Janek

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Suggested policy: use declarative names for tests instead of increasing integers
by Johan Tibell 18 Dec '12

18 Dec '12

Hi, I find our tests to be quite hard to navigate, as the majority have names like tc12345.hs or some such. I suggest we instead use descriptive names like GADT.hs or PrimOps.hs instead. What do people think? -- Johan

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Need workaround for lack of fromIntegral/Int->Word rules in 7.4.2
by Johan Tibell 18 Dec '12

18 Dec '12

I'm trying to work around the lack of some fromIntegral/Int->Word rules in 7.4.2. I tried something like: int2Word :: Int -> Word #if defined(__GLASGOW_HASKELL__) int2Word (I# i#) = W# (int2Word# i#) #else int2Word = fromIntegral #endif {-# RULES "fromIntegral/Int->Word" fromIntegral = int2Word #-} but that didn't work as some fromSmallInteger and integerToWord function calls got inserted before my rule had a chance to fire. Can anyone think of a workaround that would work with 7.4.2? P.S. The reason I want this workaround is that some of my users are stuck on 7.4.2 and this regression is affecting them quite badly, making me want to try to fix it in my library. Cheers, Johan

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building GHC for Slackware/Salix
by tim.beech 17 Dec '12

17 Dec '12

I'm making a GHC package for Salix 14 (which is backwards-compatible with Slackware, so this will be a Slackware package, too). The main thing I'd be grateful for advice on is the overall approach I'm taking to the package. Others I've seen (such as the Arch package) just assume GHC is already present. My build script unpacks the binary distribution for "unknown linux" and builds GHC against that. (Both are version 7.4.2.) I have avoided installing anything else (such as the Haskell Platform) so as to keep as close as possible to the ideal of a package as a transparent, reproducible process that only depends on the source. As far as I can tell from the build prerequisites http://hackage.haskell.org/trac/ghc/wiki/Building/Preparation/Tools the only consequence is that documentation is only created as html, not pdf and ps as well. Though everything seems to work ok, the build as it stands fails three tests: Unexpected failures: lib/Time T5430 [bad stdout] (normal) perf/compiler parsing001 [stat not good enough] (normal) simplCore/should_compile spec-inline [stderr mismatch] (optasm) That is after running the fast version of the test suite, which the documentation says should pass 100%. My second question is, do these results suggest anything as to where the problem may lie, and how important it is? When I then installed the new package and built the Haskell Platform against it (using the build script at http://slackbuilds.org) although the installation nonetheless appeared to be succesful, the build script failed at the very end where it tries to do ghc-pkg recache When I did this manually, I discovered root permissions were needed. Is that normal?

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How do we best make sure {Int,Word,Float,Double} to {Int,Word,Float,Double} conversions stay efficient
by Johan Tibell 17 Dec '12

17 Dec '12

Hi, I've been tracking down a few (unrelated) performance bugs related to conversions between primitive types. What these issues had in common is that some rule failed to fire and the conversion went via Integer, killing performance. How do we best write a test that make sure that fromIntegral conversions between these types don't regress? Is it possible to test the output of the simplifier or do we have to do something less direct, like writing a loop that does such conversions and make sure that the allocation stay low? -- Johan

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