September 2011 - Glasgow-haskell-users

Re: Parallel --make (GHC build times on newer MacBook Pros?)
by Evan Laforge 05 Sep '11

05 Sep '11

> Ah, but you're measuring the startup time of ghc --make, which is not the same as the work that each individual ghc would do if ghc were invoked separately on each module, for two reasons: Excellent, sign me up for this plan then :) ghc on a single file is very quick.

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GHC build times on newer MacBook Pros?
by Johan Tibell 05 Sep '11

05 Sep '11

Hi! I'm looking to upgrade my laptop so that I can (among other things) compile GHC faster. I'll either get the 13" 2.7GHz dual-core Intel Core i7 model or the 15" 2.2GHz quad-core Intel Core i7 model. Anyone know if it's worth to get the 15" model? According to these benchmarks it should be quite a bit faster: http://www.primatelabs.ca/geekbench/mac-benchmarks/ but I don't know if I can get enough parallelism out of GHC's build to use all 4 cores in the 15" model. -- Johan

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Superclass defaults
by Simon Peyton-Jones 05 Sep '11

05 Sep '11

(Adding GHC users, and changing title.) | Conor McBride wrote: | > http://hackage.haskell.org/trac/ghc/wiki/DefaultSuperclassInstances | > I don't know if it's likely to be implemented in GHC anytime soon,.. | > So things are looking up. It should soon be technically feasible to | > separate the issues of whether the Monoid operator should be (<>) and | > whether it should actually live in a Semigroup superclass... | | Nice. But will it be happening soon, or not? And how soon is | soon? Not soon enough to be useful for this mappend question. But, concerning proposed extensions to GHC about class aliases/superclass defaults etc, the truth is that the biggest reason for inertia here at GHC HQ is not so much the implementation effort (athough that is always an issue). Rather, it's uncertainty about (a) Is there a reasonably large group of users who really want such a change? Or is it just "nice to have"? (b) What is the "right" design? (c) Does it pay its way? (ie do the programming benefits justify the cost in terms of both language complexity and ongoing maintenance burden of one more feature to bear in mind when changing anything) With help from Conor we have made some progress on this: we have a draft design: http://hackage.haskell.org/trac/ghc/wiki/DefaultSuperclassInstances If you care about the issue, maybe you can help resolve the above questions. In particular, to give concrete evidence for (b), working out some case studies would be a Good Thing. The examples given in other proposals using the extension proposed here would be one starting point. If someone felt able to act as moderator for the discussion, willing to summarise conclusions, open questions, and so on, on the wiki page, that would be enormously helpful. I am in too many inner loops. But I *am* willing to contemplate such an extension -- it has the same flavour as default methods themselves, which are a very useful part of H98. Simon

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Panic when using syb with GHC API
by Simon Hengel 01 Sep '11

01 Sep '11

Hello, I'm trying to query a type-checked module with syb, this works for a plain binding. But as soon as I add a type signature for that binding, I get an "panic!" I experienced similar problems with a renamed module. Are those data structures meant to be used with syb? And if yes, what did I miss? Bellow is some code to reproduce my issue. Any help is very much appreciated. -- A.hs module Main where import GHC import Outputable import Data.Generics import GHC.Paths (libdir) import Bag main :: IO () main = do m <- parse putStrLn $ showSDoc $ ppr $ m putStrLn "\n---\n" putStrLn $ showSDoc $ ppr $ selectAbsBinds m parse = runGhc (Just libdir) $ do _ <- getSessionDynFlags >>= setSessionDynFlags target <- guessTarget "B.hs" Nothing setTargets [target] Succeeded <- load LoadAllTargets modSum <- getModSummary $ mkModuleName "B" m <- parseModule modSum >>= typecheckModule return $ typecheckedSource m selectAbsBinds :: GenericQ [HsBindLR Id Id] selectAbsBinds = everything (++) ([] `mkQ` f) where f x@(AbsBinds _ _ _ _ _) = [x] f _ = [] -- B.hs module B where foo :: Char foo = 'f' Cheers, Simon

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