[Haskell-cafe] cpphs calls error when it finds an #error declaration
Hi, after some debugging of a higher-level tool I found out that when I use cpphs as a library and the `runCpphs` function that is to produce the preprocessed output, when it comes across the #error directive it will terminate my program. This is because handling #error is implemented with Haskell's `error`. I find that slightly unfortunate since it means I cannot distinguish betwen an #error written in the input file and a programming error inside cpphs. @Malcolm, would you mind a change towards throwing an exception that is different from error so that it can be easily caught, or even better, a change from runCpphs :: ... -> IO String to runCpphs :: ... -> IO (Either String String) or similar? If an exception based interface is kept, it would be nice to add some haddock to `runCpphs`; not knowing about the existence of #error, it is easy to assume that the IO is only used for accessing the FilePath passed in. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Template Haskell
Hi Jose, Template Haskell doesn't parse code. haskell-src-exts and the GHC API can do that. Have a look at: * ghc-mod browse (using ghc api) * hscope (using haskell-src-exts) On 27/08/13 15:45, Jose A. Lopes wrote: > Hi, > > Is it possible to retrieve all definitions contained in a module using > Template Haskell ? > > Thanks, > Jose > ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Template Haskell
Thanks, Jose -- Jose Antonio Lopes Ganeti Engineering Google Germany GmbH Dienerstr. 12, 80331, München Registergericht und -nummer: Hamburg, HRB 86891 Sitz der Gesellschaft: Hamburg Geschäftsführer: Graham Law, Christine Elizabeth Flores Steuernummer: 48/725/00206 Umsatzsteueridentifikationsnummer: DE813741370 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] sequence causing stack overflow on pretty small lists
On Mon, Aug 26, 2013 at 4:46 AM, Niklas Hambüchen wrote: > On #haskell we recently had a discussion about the following: > >import System.Random > >list <- replicateM 100 randomIO :: IO [Int] > > I would think that this gives us a list of a million random Ints. In > fact, this is what happens in ghci. But with ghc we get: > >Stack space overflow: current size 8388608 bytes. >Use `+RTS -Ksize -RTS' to increase it. > > You can use ContT to force the function to use heap instead of stack space, e.g. runContT (replicateM 100 (lift randomIO)) return ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] sequence causing stack overflow on pretty small lists
On 27/08/13 20:37, Patrick Palka wrote: > You can use ContT to force the function to use heap instead of stack > space, e.g. runContT (replicateM 100 (lift randomIO)) return That is interesting, and works. Unfortunately its pure existence will not fix sequence, mapM etc. in base. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] sequence causing stack overflow on pretty small lists
On Mon, Aug 26, 2013 at 12:05:14PM -0700, Bryan O'Sullivan wrote: > On Mon, Aug 26, 2013 at 1:46 AM, Niklas Hambüchen wrote: > > This is because sequence is implemented as > > > > sequence (m:ms) = do x <- m > > xs <- sequence ms > > return (x:xs) > > > > and uses stack space when used on some [IO a]. > > > > This problem is not due to sequence, which doesn't need to add any > strictness here. It occurs because the functions in System.Random are > excessively lazy. In particular, randomIO returns an unevaluated thunk. I don't understand this. The same stack overflow occurs with tenmil :: Int tenmil = 10 * 1000 * 1000 main :: IO () main = do list <- replicateM tenmil (return ()) :: IO [()] list `seq` return () "return ()" is not excessiely lazy, is it? Could you explain further? Tom ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] enumerators: exception that can't be catched
Hello, I'm debugging an issue in "websockets" package, https://github.com/jaspervdj/websockets/issues/42 I'm not familiar with "enumerator" package (websockets are based on it), so I'm looking for help. The exception is throws inside "enumSocket" enumerator using "throwError" ( http://hackage.haskell.org/packages/archive/network-enumerator/0.1.5/doc/html/src/Network-Socket-Enumerator.html#enumSocket ), but I can't catch it with "catchError". It is propagated to "run" function: : recv: resource vanished (Connection reset by peer) The question is: how is it possible? could it be a bug in "enumerator" package? Thanks, Yuras ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] enumerators: exception that can't be catched
This is partially guesswork, but the code to catchWSError looks dubious: catchWsError :: WebSockets p a -> (SomeException -> WebSockets p a) -> WebSockets p a catchWsError act c = WebSockets $ do env <- ask let it = peelWebSockets env $ act cit = peelWebSockets env . c lift $ it `E.catchError` citwhere peelWebSockets env = flip runReaderT env . unWebSockets Look at `cit`. It runs the recovery function, then hands the underlying Iteratee the existing environment. That's fine if `act` is at fault, but there are Iteratee- and IO-ish things in WebSocketsEnv---if one of `envSink` or `envSendBuilder` is causing the exception, it'll just get re-thrown after `E.catchError`. (I think. That's the guesswork part.) So check how `envSendBuilder` is built up, and see if there's a way it could throw an exception on client disconnect. On Tue, Aug 27, 2013 at 10:28 AM, Yuras Shumovich wrote: > Hello, > > I'm debugging an issue in "websockets" package, > https://github.com/jaspervdj/websockets/issues/42 > > I'm not familiar with "enumerator" package (websockets are based on it), > so I'm looking for help. The exception is throws inside "enumSocket" > enumerator using > "throwError" ( > http://hackage.haskell.org/packages/archive/network-enumerator/0.1.5/doc/html/src/Network-Socket-Enumerator.html#enumSocket), > but I can't catch it with "catchError". It is propagated to "run" > function: >: recv: resource vanished (Connection reset by peer) > > The question is: how is it possible? could it be a bug in "enumerator" > package? > > Thanks, > Yuras > > > ___ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Template Haskell: let statement in a splice put in the "main = do" part of a program?
adam vogt wrote:
> TH quotes limited as you've noticed. One way to generate similar code
> is to note that:
>
> do
> let x = y
> z
>
> is the same as let x = y in do z. You can generate the latter with
> something like the following file, but the `a' isn't in scope for the
> second argument to makeLetStatement. The uglier $(dyn "a") works,
> though I suppose it's more verbose than manually in-lining the
> variable a.
>
> {-# LANGUAGE TemplateHaskell #-}
> import Language.Haskell.TH
>
> main = $(let
>
> makeLetStatement :: String -> ExpQ -> ExpQ
> makeLetStatement s rest = letE [ valD (varP (mkName s))
> (normalB $ stringE s) []]
> rest
>
> in makeLetStatement "a" [| print $(dyn "a") |] )
Thanks Adam.
Unfortunately, this solution is not satisfying because the goal is to put
only one mention to "a" in the "main" part, putting all the repetitive code
and ExpQ's in a separate module. Tonight, I've tried hard one more time
without more success.
Maybe I have to stick to non-let expressions in the "main" part of a script,
when it comes to TH. It should nevertheless allow me to call functions, make
tests, etc.
Thanks,
TP
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Re: [Haskell-cafe] sequence causing stack overflow on pretty small lists
IMHO it's perfectly reasonable to expect sequence/replicateM/mapM to be able to handle a list of ~1e6 elements in the Unescapable Monad (i.e. IO). All the alternate implementations in the world won't be as handy as Prelude.sequence, and no amount of documentation will prevent people from running into this headlong*. So unless there's a downside to upping the stack size limitation I'm unaware of, +1 to that suggestion from me. John [1] Most people are physically incapable of reading documents that explain why what they want to do won't work. Even if people did read the documentation, I suspect that the people most in need of the information would be the least likely to understand how it applies to their situation. On Tue, Aug 27, 2013 at 9:19 PM, John Alfred Nathanael Chee < cheech...@gmail.com> wrote: > This is somewhat related: http://ghc.haskell.org/trac/ghc/ticket/4219 > > This also solves the concrete problem you gave in your original post > (in reverse order): > > import Control.Monad > import System.Random > > sequencel :: Monad m => [m a] -> m [a] > sequencel = foldM (\tail m -> (\x -> return $ x : tail) =<< m) [] > > main :: IO () > main = print =<< sequencel (replicate 100 (randomIO :: IO Integer)) > > Following on Reid's point, maybe it's worth noting in the > documentation that replicateM, mapM, and sequence are not tail > recursive for Monads that define (>>=) as strict in the first > argument? > > On Tue, Aug 27, 2013 at 6:07 AM, Niklas Hambüchen wrote: > > On 27/08/13 20:37, Patrick Palka wrote: > >> You can use ContT to force the function to use heap instead of stack > >> space, e.g. runContT (replicateM 100 (lift randomIO)) return > > > > That is interesting, and works. > > > > Unfortunately its pure existence will not fix sequence, mapM etc. in > base. > > > > ___ > > Libraries mailing list > > librar...@haskell.org > > http://www.haskell.org/mailman/listinfo/libraries > > > > -- > Love in Jesus Christ, John Alfred Nathanael Chee > http://www.biblegateway.com/ > http://web.cecs.pdx.edu/~chee/ > > ___ > Libraries mailing list > librar...@haskell.org > http://www.haskell.org/mailman/listinfo/libraries > ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
