November 2005 - Glasgow-haskell-users

RE: Proposal: Improved error message of "Error in array index"
by Simon Marlow 09 Nov '05

09 Nov '05

On 08 November 2005 14:44, Malcolm Wallace wrote: > Whilst we are wishing for language features, I wonder if anyone > else would be interested in being able to export/import such cpp > macros using the normal Haskell module mechanism? At the moment, > it is ugly that you need to either #include or #define your macros > separately in every module where you use them. But if the cpp phase > were integrated more tightly into the compiler, it could be possible > to treat macros almost like ordinary function definitions. *shudder* I disagree most strongly. CPP is a well-defined preprocessing stage, it is easily understood by virtue of being separate from Haskell. I don't even want to start thinking about what happens if you merge the CPP and Haskell namespaces... ugh! I guess we have a different idea of what's "ugly" :) Cheers, Simon

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RE: Proposal: Improved error message of "Error in array index"
by Simon Marlow 09 Nov '05

09 Nov '05

On 08 November 2005 23:53, John Meacham wrote: > On Tue, Nov 08, 2005 at 11:12:09AM -0000, Simon Marlow wrote: > >> One idea that occurred to us recently is this: GHCi could provide a >> simplified version of the cost-centre-stack machinery *all the time*, >> giving you a proper backtrace for any exception, at least for the >> parts of the call stack that are interpreted. We don't care about >> the cost too much - interpreted code is a lot slower than compiled >> already, and it would only be a small constant factor. I think this >> would be a huge win for debuggability. And a nice project for >> anyone who wants to hack on the GHC internals - though not a small >> task by any means. > > personally, I rarely find the stack dump very useful at all (though I > always have high hopes). perhaps I have just had bad experiences with > it, but it can often be uninformative or even misleading. It wouldn't be a dump of the evaluation stack, rather a dump of the lexical call stack - the stack that you see when you do +RTS -xc, or time profiling in GHC. It's much more useful than the evaluation stack, which is usually not terribly informative I agree (though I've heard others say they'd still like to be able to get hold of that too). Cheers, Simon

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cant bootstap ghc-6.4.1 with no ghc
by Vihang Dudhalkar 09 Nov '05

09 Nov '05

I have been attempting to bootstrap ghc-6.4.1 on a Fedora system with no previous version of ghc installed. I'm currently stuck at System/CPUTime_hsc.c. The build fails at the following point: $ distrib/hc-build --enable-hc-boot-unregistered [ many successful lines skipped ] touch GHC/PrimopWrappers.hs gmake[2]: *** No rule to make target `System/CPUTime_hsc.c', needed by `depend'. Stop. what can be the problem?? -- ___________________________________________ -----BEGIN GEEK CODE BLOCK----- Version: 3.1 GCS/S C++++ P+ L+++(++++) E++(+++) W++ N+++ w--- G++++ e+++ a-- y d- s:++ r-- b+ Y+ G+++ ------END GEEK CODE BLOCK------ decode with www.ebb.org/ungeek Linus Torvalds wrote: > Ehh.. Telling people "don't do that" simply doesn't work. Not if they can > do it easily anyway. Things really don't get fixed unless people have a > certain pain-level to induce it to get fixed. Umm... How about the following: you hit delete on patches that introduce new ioctls, I help to provide required level of pain. Deal? - Al Viro on linux-kernel

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RE: Array operations and pinning
by Simon Marlow 09 Nov '05

09 Nov '05

On 02 November 2005 11:15, Rene de Visser wrote: > Where is the documentation on how pinning works in the GHC garbage > collector (from a GHC users point of view). > > I have copied the following code from array/IO.hs and am thinking > that it is assuming that the array is pinned? What triggers the > pinning? Actually this code does not assume that any memory is pinned. It is ok to pass the underlying ByteArr# directly to C, as long as the C call is annotated "unsafe", which means that GC cannot happen while the call is running. If you want to pass ByteArr# to a "safe" C call, then you have to allocate the ByteArr# using newPinnedByteArray#. This is the only way to get a pinned object in GHC, and the only kind of pinned object that is supported is a MutByteArr# or ByteArr# (this is to simplify the GC; it doesn't need to traverse pinned objects because they don't contain any pointers, all it needs to do is remember that the memory block they occupy is still alive). Note that all this is GHC-specific; the right high-level interface to allocating pinned memory is mallocForeignPtr. > On a second note. > Why is the type signiture so constricted. The code below works on any > IOUArray (which is very usefull, not just on Int Word8). Naturally > this assumes the particular in memory array layout that GHC uses on a > particular platform, so would not be compatible (probably) with other > Haskell compilers. I think the type is right - it makes it clear that the representation being written to the file is an array of bytes. You can use castIOUArray, although that isn't ideal (it doesn't change the bounds). We should do something better here. Cheers, Simon

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Proposal: Improved error message of "Error in array index"
by Rene de Visser 08 Nov '05

08 Nov '05

>One idea that occurred to us recently is this: GHCi could provide a >simplified version of the cost-centre-stack machinery *all the time*, >Simon This still doesn't explain to me why C:\Haskell\dev>main +RTS -xc gave <GHC.Arr.CAF>main: Error in array index (This is with full profiling turned on) This sort of stack is not going to help anyone. What I think would be good is the ability to compile the executable with a top level exeception handler which goes into a low level debugger where you can examine the thunk and its surroundings. I presume that some type information is retained for the garbage collector? Enough to tell integers from pointers? Also error "Error in array index" ++ internal_show_b b ++ internal_show_i i could be done, which wouldn't have the problem of exporting unwanted show instances. Rene.

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lambda calculus theory
by Hans N Beck 08 Nov '05

08 Nov '05

Hi, I'm searching for a good mathematical oriented introduction to the theory of lambda calculus or other theoretical foundations of Lisp/ Haskell, i.e. monads or such (of course in the web there are much hints, but what is the best for mathematicans foreign to this field) Regards Hans

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RE: -ferror-spans and ghci
by Simon Marlow 08 Nov '05

08 Nov '05

On 07 November 2005 05:01, Ian Zimmerman wrote: > itz@unicorn:~/src/mindent$ ghci -ferror-spans > ___ ___ _ > / _ \ /\ /\/ __(_) > / /_\// /_/ / / | | GHC Interactive, version 6.4, for Haskell > 98. / /_\\/ __ / /___| | http://www.haskell.org/ghc/ > \____/\/ /_/\____/|_| Type :? for help. > > Loading package base-1.0 ... linking ... done. > Prelude> :a SimpleHaskell > Compiling Main ( SimpleHaskell.hs, interpreted ) > > SimpleHaskell.hs:3:0: parse error (possibly incorrect indentation) > Failed, modules loaded: none. > Prelude> Leaving GHCi. > > wth? > > It is in ghci where this option would be most useful, imho. Is it > implemented? Yes, it is implemented. Perhaps there was no reasonable span that GHC could determine for that particular error - can you show us the source file? Does 'ghc -ferror-spans' give a more detailed error? Cheers, Simon

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class aliases
by John Meacham 08 Nov '05

08 Nov '05

If I were to implement my class alias proposal for ghc in an acceptably clean way, would it be accepted? There appeared to be enough interest to support at least experimentation with it and I would have no issues with it being dropped in the future if it turned out to not be useful. (emotional attachment to code is not good practice :) ) John -- John Meacham - ⑆repetae.net⑆john⑈

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-ferror-spans and ghci
by Ian Zimmerman 07 Nov '05

07 Nov '05

itz@unicorn:~/src/mindent$ ghci -ferror-spans ___ ___ _ / _ \ /\ /\/ __(_) / /_\// /_/ / / | | GHC Interactive, version 6.4, for Haskell 98. / /_\\/ __ / /___| | http://www.haskell.org/ghc/ \____/\/ /_/\____/|_| Type :? for help. Loading package base-1.0 ... linking ... done. Prelude> :a SimpleHaskell Compiling Main ( SimpleHaskell.hs, interpreted ) SimpleHaskell.hs:3:0: parse error (possibly incorrect indentation) Failed, modules loaded: none. Prelude> Leaving GHCi. wth? It is in ghci where this option would be most useful, imho. Is it implemented? -- A true pessimist won't be discouraged by a little success.

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INSTANCE_TYPEABLEx now missing in GHC
by Vadim Konovalov 06 Nov '05

06 Nov '05

Dear all, I installed latest GHC version 6.5.20051102, and then, when compiling 'hs-plugins', I got an error about INSTANCE_TYPEABLE. Those were previously defined in 'Typeable.h' file, and copying its definition from older version makes things work. Is that change intentional? Best regards, Vadim.

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