- Glasgow-haskell-users

Re: The semantics of Core?
by Kirsten Chevalier 18 Feb '03

18 Feb '03

On Tue, Feb 18, 2003 at 12:01:02PM -0500, glasgow-haskell-users-request(a)haskell.org wrote: > I'm also looking for actual code for working with Core. :) The > Language.Haskell.* stuff gives me a very high-level representation of > Haskell source, and I'd rather work with something simple, like Core. I > *suppose* I could use ghc -fvia-ext or helium -C or something like that, > and then parse the file it spits out, but it feels like a long way to go > when there should be shortcuts available. Another way is to rip out the > code from ghc or helium that does this, but that's not so nice either :( > There is a parser, typechecker, interpreter, and printer for Core in ghc/utils/ext-core in the fptools distribution. The typechecker and interpreter don't work on Core produced by the latest version of GHC, but the parser and printer should still work OK. It's a lot easier than linking your code with code from GHC! -- Kirsten Chevalier * krc(a)uclink.berkeley.edu * Often in error, never in doubt

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permissions on ghc Windows installer?
by Malcolm Wallace 18 Feb '03

18 Feb '03

I have been attempting to solve some outstanding problems with building hmake, nhc98, and hat, using ghc under Windows. I don't have a Windows machine of my own, but our Dept has some public-access Windows 2000 Pro machines I can use. However, when I try to use the ghc .msi automatic installer package, it reports that I do not have sufficient privileges to install ghc in my own temporary disk area. Apparently it needs administrator privileges, which I do not have (and will not be able to acquire). Are administrator privileges really required? I notice that the installer for Cygwin (i.e. not ghc) explicitly allows you to choose whether to install for all users or "just for me". Would it be difficult to allow the same choice in the ghc installer? Regards, Malcolm

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18 Feb '03

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RE: Question about compiling CGIs with Ghc
by Simon Marlow 18 Feb '03

18 Feb '03

> http://www.haskell.org/ghc/docs/latest/html/network/Network.CGI.html > > This make me curious, and the following just made me curiouser... > > Forbidden > You don't have permission to access > /ghc/docs/latest/html/network/Network.CGI.html on this server. *Sigh* That's because Apache thinks it's a CGI script. I just checked the Apache documentation, which doesn't suggest any workarounds apart from renaming the file: http://httpd.apache.org/docs/mod/mod_mime.html#multipleext I've renamed the file, and the links to it, for now: http://www.haskell.org/ghc/docs/latest/html/network/Network._CGI.html Cheers, Simon

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RE: Yet another weakly defined bug report
by Simon Marlow 18 Feb '03

18 Feb '03

> The following code runs out of file handles, so I am seeking > enlightenment as to why. > > > -- | add data from a file to the histogram > > addFile :: FiniteMap String Int -> String -> IO (FiniteMap > String Int) > > addFile fm name = do > > x <- readFile name > > return (addHist fm x) > > > > -- | add data from all files in a directory to the histogram > > addDir :: FiniteMap String Int -> String -> IO (FiniteMap > String Int) > > addDir fm dir = do > > dc <- getDirectoryContents dir > > fs <- filterM doesFileExist (map ((dir++"/")++) dc) > > foldM addFile fm fs > > Running addDir on a directory with few hundred files trigs it. > Shouldn't all of each file's contents be consumed by each addFile, and > thus the handle be released? It's not possible to tell from this code whether the readFiles will be fully evaluated or not: it depends on how much evaluation addHist does, and to what extend the result FiniteMap is demanded, amongst other things. These things are always tricky to understand, which is why I recommend not using lazy I/O. File reading is not a pure operation: running out of file descriptors is a good counter-example. Cheers, Simon

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RE: The semantics of Core?
by Simon Peyton-Jones 18 Feb '03

18 Feb '03

I don't know of any separate description of the semantics of Core, but it's just the lambda calculus with let, letrec and case. There's plenty of code that works over Core in GHC itself, but no separate libraries. There is a library to parse the stuff that ghc -fext-core spits out, though. Kirsten Chevalier and Tobias Gedell have experience of using this route, and may be able to help, depending on your purpose. Contributing well-engineered Core-manipulating libraries would be a Good Thing. Simon | -----Original Message----- | From: Martin Sjögren [mailto:md9ms@mdstud.chalmers.se] | Sent: 18 February 2003 08:18 | To: glasgow-haskell-users(a)haskell.org | Subject: The semantics of Core? | | Hello | | I'm looking for a paper or some other documentation on the exact | semantics of Core. I've read the paper about the concrete syntax, and it | briefly mentions the abstract syntax and something about the case | expression, but not a lot. Unless I missed something? | | I'm also looking for actual code for working with Core. :) The | Language.Haskell.* stuff gives me a very high-level representation of | Haskell source, and I'd rather work with something simple, like Core. I | *suppose* I could use ghc -fvia-ext or helium -C or something like that, | and then parse the file it spits out, but it feels like a long way to go | when there should be shortcuts available. Another way is to rip out the | code from ghc or helium that does this, but that's not so nice either :( | | Any suggestions? | | | /Martin

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The semantics of Core?
by Martin Sjögren 18 Feb '03

18 Feb '03

Hello I'm looking for a paper or some other documentation on the exact semantics of Core. I've read the paper about the concrete syntax, and it briefly mentions the abstract syntax and something about the case expression, but not a lot. Unless I missed something? I'm also looking for actual code for working with Core. :) The Language.Haskell.* stuff gives me a very high-level representation of Haskell source, and I'd rather work with something simple, like Core. I *suppose* I could use ghc -fvia-ext or helium -C or something like that, and then parse the file it spits out, but it feels like a long way to go when there should be shortcuts available. Another way is to rip out the code from ghc or helium that does this, but that's not so nice either :( Any suggestions? /Martin

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RE: Question about compiling CGIs with Ghc
by Simon Marlow 17 Feb '03

17 Feb '03

> I have some CGI programs running with Hugs and I want to use GHC > instead. > > What changes must I do to the .hs file? > > Is it an easy job? Depends on lots of things really. The CGI library that comes with GHC is documented here: http://www.haskell.org/ghc/docs/latest/html/network/Network.CGI.html Cheers, Simon

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RE: awaitEval in Concurrent Haskell
by Simon Peyton-Jones 17 Feb '03

17 Feb '03

Does this mean you can womble along with Claus's suggestion? I'm feeling a bit swamped at the moment, and not keen to undertake another open-ended implementation exercise. So if you can manage without, and perhaps use the experience to refine the specification of a Really Useful Feature, that'd be great from my point of view. Simon | -----Original Message----- | From: Colin Runciman [mailto:colin@cs.york.ac.uk] | Sent: 17 February 2003 13:40 | To: Claus Reinke | Cc: Colin Runciman; C.Reinke; Simon Peyton-Jones; GHC users | Subject: Re: awaitEval in Concurrent Haskell | | A couple of hours ago, I wrote (in reponse to Claus Reinke's suggestion): | | > Thanks for this further suggestion. A solution along these lines | > might be | > possible, but it would still be restricted ... | | Actually a mild variant of Claus's proposal seems to work out | quite well. Another way to avoid the problems with types is | to use a multi-parameter type class. Little example attached. | | So, thanks again Claus! | | Regards | Colin R

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Re: awaitEval in Concurrent Haskell
by C.Reinke 17 Feb '03

17 Feb '03

> Colin [ccing GHC users in case there are other enthusiasts out there] > > | we briefly discussed the lack in > | Concurrent Haskell of any way to set up a data-driven > | thread -- one that works on a data structure D without > | ever forcing its evaluation, only proceeding with the > | computation over D as and when the needed parts get > | evaluated by some other thread. I'm not sure whether I understand what you have in mind later on, but this first part sounds so remarkably like something I've seen before, that I'll take my chances. Do you remember Andy Gill's Hood from long ago? Inside its implementation, it had a very similar problem: writing information about an observed structure to some observation trace, but without forcing premature evaluation of the structure under observation. The trick used in Observe.lhs is roughly this (here for (,)): observe label (a,b) = unsafePerformIO $ do sendObservation label "(,)" return (observe label a,observe label b) with some position information and strictness mangling added, and the whole nicely wrapped into a monad (see Observe.lhs for details). Nothing happens as long as the thing under observation is not inspected by its context. Then, and precisely then, the unsafePerformIO kicks in to record a piece of information and to return the outer part of the thing, wrapping its components into fresh observers. Andy used this to store observations in a list, to be processed at the end of the program run, but you can just as well send the observations during evaluation, e.g., to a concurrent thread (with the usual caveats). In particular, the sequencing of information becoming available was detailed enough to inspire my own GHood;-) With no implementation slot free, something like this might get your student's project unstuck (e.g., replace sendObservation by assert)? After all, my favourite justification for unsafePerformIO is as an extension hook in the runtime system.. Sorry if your intention was something else and I'm just trying to fit a solution to the problem. Even then, you might be able to adapt the trick to your application. Cheers, Claus

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