Re: ANNOUNCE: GHC 7.10.1 Release Candidate 3
Am 16.03.2015 um 21:30 schrieb Austin Seipp: > We are pleased to announce the third release candidate for GHC 7.10.1: > > https://downloads.haskell.org/~ghc/7.10.1-rc3 > https://downloads.haskell.org/~ghc/7.10.1-rc3/docs/html/ The current version of cabal-install located at Hackage can not be installed for the RC because of the following dependency error: Setup: At least the following dependencies are missing: filepath >=1.0 && <1.4 The problem is that cabal-install require filepath < 1.4, while the RC ships with filepath-1.4. This issue [1] has already been solved in cabal-install, so a new release available at Hackage would be desirable. Regards, Björn [1]: https://github.com/haskell/cabal/issues/2461 ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users
GHC 7.10 regression when using foldr
I just discovered that the following program compiled fine using GHC 7.8.4 but was rejected by GHC 7.10.1-rc1: ~~~ data List a = Nil | Cons a (List a) instance Read a => Read (List a) where readsPrec d s = map convert (readsPrec d s) where convert (xs, s2) = (foldr Cons Nil xs, s2) ~~~ GHC 7.10 now complains: ~~~ Read.hs:5:23: Could not deduce (Foldable t0) arising from a use of ‘convert’ from the context (Read a) bound by the instance declaration at Read.hs:4:10-32 The type variable ‘t0’ is ambiguous Note: there are several potential instances: instance Foldable (Either a) -- Defined in ‘Data.Foldable’ instance Foldable Data.Proxy.Proxy -- Defined in ‘Data.Foldable’ instance GHC.Arr.Ix i => Foldable (GHC.Arr.Array i) -- Defined in ‘Data.Foldable’ ...plus three others In the first argument of ‘map’, namely ‘convert’ In the expression: map convert (readsPrec d s) In an equation for ‘readsPrec’: readsPrec d s = map convert (readsPrec d s) where convert (xs, s2) = (foldr Cons Nil xs, s2) Read.hs:5:32: Could not deduce (Read (t0 a)) arising from a use of ‘readsPrec’ from the context (Read a) bound by the instance declaration at Read.hs:4:10-32 The type variable ‘t0’ is ambiguous Relevant bindings include readsPrec :: Int -> ReadS (List a) (bound at Read.hs:5:3) Note: there are several potential instances: instance (Read a, Read b) => Read (Either a b) -- Defined in ‘Data.Either’ instance forall (k :: BOX) (s :: k). Read (Data.Proxy.Proxy s) -- Defined in ‘Data.Proxy’ instance (GHC.Arr.Ix a, Read a, Read b) => Read (GHC.Arr.Array a b) -- Defined in ‘GHC.Read’ ...plus 18 others In the second argument of ‘map’, namely ‘(readsPrec d s)’ In the expression: map convert (readsPrec d s) In an equation for ‘readsPrec’: readsPrec d s = map convert (readsPrec d s) where convert (xs, s2) = (foldr Cons Nil xs, s2) ~~~ The reason is the usage of foldr, which changed its type from foldr :: (a -> b -> b) -> b -> [a] -> b -- GHC 7.8.4 to foldr :: Foldable t => (a -> b -> b) -> b -> t a -> b -- GHC 7.10.1 Thus, the use of foldr is now ambiguous. I can fix this by providing a type signature convert :: ([a], String) -> (List a, String) However, is this breaking change intended? Regards, Björn ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: Strange performance effects with unsafePerformIO
Simon Marlow schrieb: > Incidentally this will be faster with GHC 7.2, because we implemented > chunked stacks, so unsafePerformIO never has to traverse more than 32k > of stack (you can tweak the chunk size with an RTS option). This is > still quite a lot of overhead, but at least it is bounded. > > The example above runs in 1.45s for me with current HEAD, and I gave up > waiting with 7.0. Thank you all for your explanations, the blackholing indeed seems to be the cause for the slowdown. Is there any documentation available about the blackholing process? Maybe we can find a hint on how to change our code to avoid the problem. Regards, Bjoern ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Strange performance effects with unsafePerformIO
Hello, we have a strange performance behaviour when we use unsafePerformIO, at least with GHC 6.12.3 and 7.0.1. Please consider the example program following at the end of this post. Running the original code the execution time is about 26 seconds, while uncommenting one (or both) of the comments shrinks it to about 0.01 seconds on our machine. Is there an explanation for this effect? Regards, Bjoern -- --- module Main where import System.IO.Unsafe traverse [] = return () -- traverse (_:xs) = traverse xs traverse (_:xs) = traverse xs >> return () makeList 0 = [] -- makeList n = () : (makeList (n - 1)) makeList n = () : (unsafePerformIO . return) (makeList (n - 1)) main = traverse $ makeList (10^5) ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
