January 2014 - ghc-devs

GHC Api
by Simon Peyton-Jones 04 Jan '14

04 Jan '14

Simon and othere Happy new year! When debugging Trac #8628 I wrote the following: main = do [libdir] <- getArgs ok <- runGhc (Just libdir) $ do dflags <- getSessionDynFlags -- (1) setSessionDynFlags dflags liftIO (setUnsafeGlobalDynFlags dflags) -- (2) setContext [IIDecl (simpleImportDecl pRELUDE_NAME)] -- (3) runDecls "data X = Y Int" runStmt "print True" -- (4) return () There are several odd things here 1. Why do I have to do this "getSessionDynFlags/setSessionDynFlags" thing. Seems bizarre. I just copied it from some other tests in ghc-api/. Is it necessary? If not, can we remove it from all tests? 2. Initially I didn't have that setUnsafeGlobalDynFlags call. But then I got T8628.exe: T8628.exe: panic! (the 'impossible' happened) (GHC version 7.7.20131228 for i386-unknown-mingw32): v_unsafeGlobalDynFlags: not initialised which is a particularly unhelpful message. It arose because I was using a GHC built with assertions on, and a warnPprTrace triggered. Since this could happen to anyone, would it make sense to make this part of runGhc and setSessionDynFlags? 3. Initially I didn't have that setContext call, and got a complaint that "Int is not in scope". I was expecting the Prelude to be implicitly in scope. But I'm not sure where to fix that. Possibly part of the setup in runGhc? 4. The runStmt should print something somewhere, but it doesn't. Why not? What do you think? Simon

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Re: [commit: packages/base] master: Add functions to compare Nat and Symbol types for equality. (c5c8c4d)
by Gabor Greif 03 Jan '14

03 Jan '14

Iavor, this is great! Just out of curiosity, you import TestEquality but never reference it. Is this an oversight, should I nuke it? Cheers, Gabor On 1/4/14, git(a)git.haskell.org <git(a)git.haskell.org> wrote: > Repository : ssh://git@git.haskell.org/base > > On branch : master > Link : > http://ghc.haskell.org/trac/ghc/changeset/c5c8c4dfbdc8493bcfaa804751eff2a9a… > >>--------------------------------------------------------------- > > commit c5c8c4dfbdc8493bcfaa804751eff2a9a41cc07a > Author: Iavor S. Diatchki <diatchki(a)galois.com> > Date: Fri Jan 3 15:11:34 2014 -0800 > > Add functions to compare Nat and Symbol types for equality. > > >>--------------------------------------------------------------- > > c5c8c4dfbdc8493bcfaa804751eff2a9a41cc07a > GHC/TypeLits.hs | 23 ++++++++++++++++++++++- > 1 file changed, 22 insertions(+), 1 deletion(-) > > diff --git a/GHC/TypeLits.hs b/GHC/TypeLits.hs > index f3ba70e..129beb3 100644 > --- a/GHC/TypeLits.hs > +++ b/GHC/TypeLits.hs > @@ -26,6 +26,8 @@ module GHC.TypeLits > , KnownSymbol, symbolVal > , SomeNat(..), SomeSymbol(..) > , someNatVal, someSymbolVal > + , sameNat, sameSymbol > + > > -- * Functions on type nats > , type (<=), type (<=?), type (+), type (*), type (^), type (-) > @@ -40,7 +42,8 @@ import GHC.Read(Read(..)) > import GHC.Prim(magicDict) > import Data.Maybe(Maybe(..)) > import Data.Proxy(Proxy(..)) > -import Data.Type.Equality(type (==)) > +import Data.Type.Equality(type (==), TestEquality(..), (:~:)(Refl)) > +import Unsafe.Coerce(unsafeCoerce) > > -- | (Kind) This is the kind of type-level natural numbers. > data Nat > @@ -167,6 +170,23 @@ type family (m :: Nat) ^ (n :: Nat) :: Nat > type family (m :: Nat) - (n :: Nat) :: Nat > > > +-------------------------------------------------------------------------------- > + > +-- | We either get evidence that this function was instantiated with the > +-- same type-level numbers, or 'Nothing'. > +sameNat :: (KnownNat a, KnownNat b) => > + Proxy a -> Proxy b -> Maybe (a :~: b) > +sameNat x y > + | natVal x == natVal y = Just (unsafeCoerce Refl) > + | otherwise = Nothing > + > +-- | We either get evidence that this function was instantiated with the > +-- same type-level symbols, or 'Nothing'. > +sameSymbol :: (KnownSymbol a, KnownSymbol b) => > + Proxy a -> Proxy b -> Maybe (a :~: b) > +sameSymbol x y > + | symbolVal x == symbolVal y = Just (unsafeCoerce Refl) > + | otherwise = Nothing > > -------------------------------------------------------------------------------- > -- PRIVATE: > @@ -187,3 +207,4 @@ withSSymbol :: (KnownSymbol a => Proxy a -> b) > -> SSymbol a -> Proxy a -> b > withSSymbol f x y = magicDict (WrapS f) x y > > + > > _______________________________________________ > ghc-commits mailing list > ghc-commits(a)haskell.org > http://www.haskell.org/mailman/listinfo/ghc-commits >

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Re: Idea for improving communication between devs and potential devs
by Howard B. Golden 03 Jan '14

03 Jan '14

Chris, Thanks for the pointer to HWN. I wasn't aware of it before. I can certainly send things to the author which may be of interest to readers. In addition I like incorporating the updates into the GHC Devs wiki to make it easier to find them that way. We each have our preferred way of keeping up-to-date. Howard

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Re: Idea for improving communication between devs and potential devs
by Chris Heller 03 Jan '14

03 Jan '14

I think a weekly summary like what LWN provides would be very valuable. Perhaps there is an opportunity to piggy-back this on the work of the Haskell Weekly News project ( http://contemplatecode.blogspot.com/search/label/HWN) -Chris

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Type-level reasoning ability lost for TypeLits?
by Gabor Greif 03 Jan '14

03 Jan '14

Hi devs, with recent iterations of GHC.TypeLits (HEAD) I am struggling to get something simple working. I have > data Number nat = KnownNat nat => Number !(Proxy nat) and want to write > addNumbers :: Number a -> Number b -> Maybe (Number (a + b)) Unfortunately I cannot find a way to create the necessary KnownNat (a + b) constraint. Declaring the function thus > addNumbers :: KnownNat (a + b) => Number a -> Number b -> Maybe (Number (a + b)) only dodges the problem around. Also I am wondering where the ability to perform a type equality check went. I.e. I cannot find the relevant functionality to obtain > sameNumber :: Number a -> Number b -> Maybe (a :~: b) I guess there should be some TestEquality instance (for Proxy Nat?, is this possible at all), but I cannot find it. Same applies for Symbols. Any hints? Thanks and cheers, Gabor

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Building GHC head with clang on Mavericks
by Kazu Yamamoto 03 Jan '14

03 Jan '14

Hi, As I wrote in the following blog article, I could build GHC head on Mavericks 20 days ago. http://d.hatena.ne.jp/kazu-yamamoto/20131028/1382921924 But I cannot build it recently: ---- "/usr/bin/ghc" -hisuf hi -osuf o -hcsuf hc -static -H32m -O -package-db libraries/bootstrapping.conf -i -iutils/genprimopcode/. -iutils/genprimopcode/dist/build -iutils/genprimopcode/dist/build/autogen -Iutils/genprimopcode/dist/build -Iutils/genprimopcode/dist/build/autogen -package array -no-user-package-db -rtsopts -odir utils/genprimopcode/dist/build -hidir utils/genprimopcode/dist/build -stubdir utils/genprimopcode/dist/build -c utils/genprimopcode/dist/build/Lexer.hs -o utils/genprimopcode/dist/build/Lexer.o <built-in>:2:2: Not in scope: `#' make[1]: *** [utils/genprimopcode/dist/build/Lexer.o] Error 1 make[1]: *** Waiting for unfinished jobs.... shift/reduce conflicts: 46 reduce/reduce conflicts: 1 make: *** [all] Error 2 ---- I seems to me that linemarkers generated by GCC(CPP) is not correctly handled when alex is used. Note I can build GHC head on FreeBSD and Linux. I'm using clang with clang-xcode5-wrapper.hs. Any suggestions? --Kazu

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Re: Re: [commit: packages/base] master: Improve error messages for partial functions in Data.Data (d0b74ca) (Gabor Greif)
by Krzysztof Langner 02 Jan '14

02 Jan '14

Hi Gabor, Thank you for the feedback. You are right about spelling. I'll fix it. Regarding refactoring: If I understand you correctly your suggestion is to add new function which will wrap error message so the text will be less redundant. I'm not sure about it. From my experience it is better to leave error messages as simple as possible. Since when using functions in error messages it is possible that this function will fail and then you will get confusing error message (from inside function). So as a rule of thumb I never add another functions inside error processing (except the ones which makes message more meaningful). But that's of course just my point of view. It is also possible that I didn't understand your proposition correctly :-) -- Thanks Krzysztof

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Re: [commit: packages/base] master: Improve error messages for partial functions in Data.Data (d0b74ca)
by Gabor Greif 01 Jan '14

01 Jan '14

On 1/1/14, git(a)git.haskell.org <git(a)git.haskell.org> wrote: > Repository : ssh://git@git.haskell.org/base > > On branch : master > Link : > http://ghc.haskell.org/trac/ghc/changeset/d0b74cac0b0ab5371d15b6f73c0e627b4… > >>--------------------------------------------------------------- > > commit d0b74cac0b0ab5371d15b6f73c0e627b41c3a152 > Author: Krzysztof Langner <klangner(a)gmail.com> > Date: Wed Jan 1 14:14:46 2014 +0100 > > Improve error messages for partial functions in Data.Data > > This closes: #5412 Hi Krzysztof, there are typos "an Real" --> "a Real" but this actually your commit begs for a refactoring > "something" `notAsExpected` "a Real" etc. as it would eliminate a bunch of (string) redundancy. Cheers, Gabor > > >>--------------------------------------------------------------- > > d0b74cac0b0ab5371d15b6f73c0e627b41c3a152 > Data/Data.hs | 76 > ++++++++++++++++++++++++++++++++++++++++------------------ > 1 file changed, 53 insertions(+), 23 deletions(-) > > Diff suppressed because of size. To see it, use: > > git diff-tree --root --patch-with-stat --no-color --find-copies-harder > --ignore-space-at-eol --cc d0b74cac0b0ab5371d15b6f73c0e627b41c3a152 > _______________________________________________ > ghc-commits mailing list > ghc-commits(a)haskell.org > http://www.haskell.org/mailman/listinfo/ghc-commits >

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