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[Haskell-cafe] Announcing Djinn, version 2004-12-11, a coding wizard
by Lennart Augustsson 15 Dec '05

15 Dec '05

Howdy, y'all! I've written a small program that takes a (Haskell) type and gives you back a function of that type if one exists. It's kind of fun, so I thought I'd share it. It's probably best explained with a sample session. calvin% djinn Welcome to Djinn version 2005-12-11. Type :h to get help. # Djinn is interactive if not given any arguments. # Let's see if it can find the identity function. Djinn> f ? a->a f :: a -> a f x1 = x1 # Yes, that was easy. Let's try some tuple munging. Djinn> sel ? ((a,b),(c,d)) -> (b,c) sel :: ((a, b), (c, d)) -> (b, c) sel ((_, v5), (v6, _)) = (v5, v6) # We can ask for the impossible, but then we get what we # deserve. Djinn> cast ? a->b -- cast cannot be realized. # OK, let's be bold and try some functions that are tricky to write: # return, bind, and callCC in the continuation monad Djinn> type C a = (a -> r) -> r Djinn> returnC ? a -> C a returnC :: a -> C a returnC x1 x2 = x2 x1 Djinn> bindC ? C a -> (a -> C b) -> C b bindC :: C a -> (a -> C b) -> C b bindC x1 x2 x3 = x1 (\ c15 -> x2 c15 (\ c17 -> x3 c17)) Djinn> callCC ? ((a -> C b) -> C a) -> C a callCC :: ((a -> C b) -> C a) -> C a callCC x1 x2 = x1 (\ c15 _ -> x2 c15) (\ c11 -> x2 c11) # Well, poor Djinn has a sweaty brow after deducing the code # for callCC so we had better quit. Djinn> :q Bye. To play with Djinn do a darcs get http://darcs.augustsson.net/Darcs/Djinn or get http://darcs.augustsson.net/Darcs/Djinn/Djinn.tar.gz Then just type make. (You need a Haskell 98 implementation and some libraries.) And then start djinn. For the curious, Djinn uses a decision procedure for intuitionistic propositional calculus due to Roy Dyckhoff. It's a variation of Gentzen's LJ system. This means that (in theory) Djinn will always find a function if one exists, and if one doesn't exist Djinn will terminate telling you so. This is the very first version, so expect bugs. :) Share and enjoy. -- Lennart

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RE: [Haskell-cafe] Top-level TVars
by Simon Marlow 15 Dec '05

15 Dec '05

On 14 December 2005 10:11, Joel Reymont wrote: > I'm a bit lost in the discussion. Why do I need -fno-cse and how do I > seq at the top-level? > > On Dec 14, 2005, at 10:05 AM, Tomasz Zielonka wrote: > >> On Wed, Dec 14, 2005 at 10:03:42AM -0000, Simon Marlow wrote: >>> Well sure, but it's only a temporary problem. And you also have to >>> tell them to use {-# NOINLINE #-} and -fno-cse :-) >> >> -fno-cse is also neccesary? Oops, I didn't know that. Can I simply >> place it in {-# OPTIONS -fno-cse #-} ? Suppose you create two top-level IORefs with the same type, like this: var1 = unsafePerformIO $ newIORef 0 var2 = unsafePerformIO $ newIORef 0 GHC's CSE optimisation will common these up - after all, it's the same expression, so it must yield the same result, right? To turn this off, we use -fno-cse. It's good practice to use -fno-cse whenever you use top-level mutable objects of any kind. You can put it in the source file: {-# OPTIONS_GHC -fno-cse #-} at the top of your file. Cheers, Simon

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RE: [Haskell-cafe] killThread and FFI calls
by Simon Marlow 15 Dec '05

15 Dec '05

On 14 December 2005 15:35, Joel Reymont wrote: > On Dec 14, 2005, at 3:22 PM, Simon Marlow wrote: > >> On 14 December 2005 14:26, Joel Reymont wrote: >> >>> How does killThread work with FFI calls? What happens at the low >>> level when a thread is blocked on an FFI call and received a >>> KillThread exception? Does it exit immediately via some GHC magic or >>> is the exception caught when the FFI call returns? >> >> The latter. > > Does this change if I kill a thread that's blocked on I/O in a > threaded runtime? > > Does it get cleaned up immediately? A thread blocked on ordinary Handle-based I/O can be killed, because blocked Handle I/O is implemented using communication with the I/O manager thread, so it isn't an FFI call under the hood. Cheers, Simon

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RE: [Haskell-cafe] killThread and FFI calls
by Simon Marlow 14 Dec '05

14 Dec '05

On 14 December 2005 14:26, Joel Reymont wrote: > How does killThread work with FFI calls? What happens at the low > level when a thread is blocked on an FFI call and received a > KillThread exception? Does it exit immediately via some GHC magic or > is the exception caught when the FFI call returns? The latter. Cheers, Simon

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RE: [Haskell-cafe] Unbound threads and FFI
by Simon Marlow 14 Dec '05

14 Dec '05

On 14 December 2005 14:37, Joel Reymont wrote: > How do unbound threads play with FFI? According to Simon PJ, each > foreign call will get its own OS thread if its blocked. > > How does GHC determine if the call is blocked? Does each call get its > own OS thread from the start? Sometime later? When a thread exits Haskell to make an FFI call, another OS thread takes over running the other Haskell threads. If we don't have another OS thread available, we start one. > Does this depend on the safe/unsafe specs of the foreign call? this only happens for safe calls, not unsafe. > Does the above change if a threaded/non-threaded runtime is in use? this only happens in the -threaded RTS, in the non-threaded RTS a FFI call will block all the other Haskell threads. Cheers, Simon

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GHC internal error: traverse_weak_ptr_list: not WEAK
by Joel Reymont 14 Dec '05

14 Dec '05

loadtest: internal error: traverse_weak_ptr_list: not WEAK Please report this as a bug to glasgow-haskell-bugs(a)haskell.org, or http://www.sourceforge.net/projects/ghc/ Has anyone seen this before? I got this after running a 1,300 socket connections for a while (probably x3 threads overall). Any workarounds? Thanks, Joel -- http://wagerlabs.com/

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Unbound threads and FFI
by Joel Reymont 14 Dec '05

14 Dec '05

How do unbound threads play with FFI? According to Simon PJ, each foreign call will get its own OS thread if its blocked. How does GHC determine if the call is blocked? Does each call get its own OS thread from the start? Sometime later? Does this depend on the safe/unsafe specs of the foreign call? Does the above change if a threaded/non-threaded runtime is in use? Thanks, Joel -- http://wagerlabs.com/

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killThread and FFI calls
by Joel Reymont 14 Dec '05

14 Dec '05

Folks, How does killThread work with FFI calls? What happens at the low level when a thread is blocked on an FFI call and received a KillThread exception? Does it exit immediately via some GHC magic or is the exception caught when the FFI call returns? Thanks, Joel -- http://wagerlabs.com/

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Announcing Djinn, new version 2004-12-13
by Lennart Augustsson 14 Dec '05

14 Dec '05

There is a new version of Djinn available, with two notable new features: Haskell data types can be defined and the found functions are sorted (heuristically) to present the best one first. To play with Djinn do a darcs get http://darcs.augustsson.net/Darcs/Djinn or get http://darcs.augustsson.net/Darcs/Djinn/Djinn.tar.gz Then just type make. (You need a Haskell 98 implementation and some libraries.) And then start djinn. `-- Lennart

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RE: [Haskell-cafe] Re: Bringing Erlang to Haskell
by Simon Peyton-Jones 14 Dec '05

14 Dec '05

There's a (GHC-specific) Wiki page on concurrent programming in GHC, in the new GHC Wiki. http://hackage.haskell.org/trac/ghc/wiki/GhcConcurrency Feel free to add more info to it. I've dropped in the links below. Simon | -----Original Message----- | From: haskell-cafe-bounces(a)haskell.org [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of | Robert Dockins | Sent: 13 December 2005 15:18 | To: Joel Reymont | Cc: Haskell-Cafe Cafe | Subject: Re: [Haskell-cafe] Re: Bringing Erlang to Haskell | | BTW, there has already been some work in this area. | | http://www-i2.informatik.rwth-aachen.de/~stolz/dhs/ | http://www.informatik.uni-kiel.de/~fhu/PUBLICATIONS/1999/ifl.html | | | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe

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