- Glasgow-haskell-users

Re: wait(2) [Slight correction]
by Mike Gunter 27 Jul '01

27 Jul '01

[My previous message omitted a word ("records"). I should take one more look at these things before sending them.] Scsh (Scheme Shell) has a mechanism to turn the Unix process interface into something reasonable. Instead of PIDs, fork returns a process object. The SIGCHLD signal handler reaps processes and records their exit status. The program can retrieve the exit status using the process object. When the process object is GCed, the status can be as well. This seems be right for almost all code (and reaping policy can be changed for the remaining code.) The details of Scsh's mechanism can be found in the manual ftp://ftp-swiss.ai.mit.edu/pub/su/scsh/scsh-manual.ps on pages 55-58. mike

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Re: wait(2)
by Mike Gunter 27 Jul '01

27 Jul '01

Scsh (Scheme Shell) has a mechanism to turn the Unix process interface into something reasonable. Instead of PIDs, fork returns process objects. The SIGCHLD signal handler reaps processes and their exit status. The program can retrieve the exit status using the process object. If the process object is GCed, the status can be as well. This seems be right for almost all code (and reaping policy can be changed for the remaining code.) The details of Scsh's mechanism can be found in the manual ftp://ftp-swiss.ai.mit.edu/pub/su/scsh/scsh-manual.ps on pages 55-58. mike

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gcc & GHC?
by hooh pxw 27 Jul '01

27 Jul '01

h(eye), ghc for win32 isn't cool. it remind me java in gcc 3.0. is there any ghc project as gcc front-end? then, we all happy on the technology of the GCC 3.0. mercury, also the front end of the gcc. http://gcc.gnu.org/frontends.html i am end user, so don't get me heavy/serious! Ah! john backus's FP.. sorry for random/ugly keyboard typing!! __________________________________________________ Do You Yahoo!? Make international calls for as low as $.04/minute with Yahoo! Messenger http://phonecard.yahoo.com/

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wait(2)
by George Russell 27 Jul '01

27 Jul '01

Is there a way in Glasgow Haskell to get a thread to wait on a child process in the same way as the Posix function wait(), and get the termination status of the child? If so, how?

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Re: wait(2)
by Marcin 'Qrczak' Kowalczyk 26 Jul '01

26 Jul '01

Thu, 26 Jul 2001 16:44:57 +0200, George Russell <ger(a)tzi.de> pisze: > Is there a way in Glasgow Haskell to get a thread to wait on a > child process in the same way as the Posix function wait(), and > get the termination status of the child? There is no easy way: all Haskell's thread run in the same process and wait() blocks the whole process. The only (or the only portable) way is to call wait() with WNOHANG repeatedly in a thread and threadDelay for a short period of time between calls. This is what OCaml runtime does. It provides waiting for a process as a threading primitive. It accounts for waiting in its select() loop in the scheduler. -- __("< Marcin Kowalczyk * qrczak(a)knm.org.pl http://qrczak.ids.net.pl/ \__/ ^^ SYGNATURA ZASTÊPCZA QRCZAK

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RE: wait(2)
by Simon Marlow 26 Jul '01

26 Jul '01

> Is there a way in Glasgow Haskell to get a thread to wait on > a child process > in the same way as the Posix function wait(), and get the > termination status > of the child? If so, how? There's a couple of ways. The obvious way is to get the thread to place its result in an MVar when it exits: there's a guarantee that a thread always either exits or raises an exception, so you can wrap the top-level computation in something that places the result/exception in an MVar. Alternatively, you can foreign import rts_evalIO() and do it that way. It ought to work, but I haven't tried it. This way lets you get at the Interrupted or Deadlocked return states too, which you can't do solely within Haskell. Hmm, now I think about it, the compiler won't let you foreign import rts_evalIO() with the type you want, namely a -> Ptr b -> IO CInt, and quite rightly so. You'll need a version of rts_evalIO() that takes StablePtrs instead. Cheers, Simon

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Rationals
by Amanda Clare 26 Jul '01

26 Jul '01

Does anyone know how I use Rationals in ghc? In nhc I can just write let a = b % c But ghc-5.00.2 gives the error message "Variable not in scope: `%'" I've looked through the documentation and can't find any reference to a Rational library, or any other library that might have it. The package "std" has a Ratio.hi in the lib/imports directory (std isn't described in the documentation) but including this doesn't help - same error. The Haskell98 report says: "In particular, the type Rational is a ratio of two Integer values, as defined in the Rational library." Any ideas? Amanda -- Amanda Clare http://users.aber.ac.uk/ajc99/ Tel: +44 (0)1970 621922 Fax: +44 (0)1970 622455 Dept. of Computer Science, University of Wales, Aberystwyth, SY23 3DB

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Re: Trying to make Hood work with GHC
by Mike Gunter 25 Jul '01

25 Jul '01

Below are the diffs I used to get from the 4.08 version to one that compiles and seems to work with 5.00. mike diff -c -a -r1.1 Observe.lhs *** Observe.lhs 10 Jan 2001 16:21:12 -0000 1.1 --- Observe.lhs 25 Jul 2001 16:44:09 -0000 *************** *** 107,113 **** \begin{code} import Exception ( catchAll ! , Exception(..) , throw , catchAllIO ) --- 107,113 ---- \begin{code} import Exception ( catchAll ! , Exception(..), IOException , throw , catchAllIO ) *************** *** 269,275 **** generate an IOError with a bottom in it, your just asking for trouble. \begin{code} ! instance Observable IOError where { observer = observeBase } \end{code} Functions. --- 269,275 ---- generate an IOError with a bottom in it, your just asking for trouble. \begin{code} ! instance Observable IOException where { observer = observeBase } \end{code} Functions. Alain Cremieux <alcremi(a)pobox.com> writes: > Hi, > I'm currently trying to have Hood work with GHC, but I have some > problems > - I have succeeded in using the hugs version of Hood > - I have dowloaded the GHC version (slightly different) but the > compilation of the 'Observe' modules fails (the module is supposed to > work with GHC 4.08 and I have GHC 5.00.2) : ...

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Trying to make Hood work with GHC
by Alain Cremieux 25 Jul '01

25 Jul '01

Hi, I'm currently trying to have Hood work with GHC, but I have some problems - I have succeeded in using the hugs version of Hood - I have dowloaded the GHC version (slightly different) but the compilation of the 'Observe' modules fails (the module is supposed to work with GHC 4.08 and I have GHC 5.00.2) : Duplicate instance declarations: Observe.lhs:272: Observable IOError Observe.lhs:291: Observable Exception with the following command-line : ghc -fglasgow-exts -package lang -package concurrent Observe.lhs corresponding to the source : instance Observable IOError where { observer = observeBase } instance Observable Exception where observer (IOException a) = send "IOException" (return IOException << a) observer (ErrorCall a) = send "ErrorCall" (return ErrorCall << a) observer other = send "<Exception>" (return other) I don't understant why there are duplicate instance declarations. Furthermore, removing them leads to : Observe.lhs:182: No instance for `Observable Exception' arising from use of `<<' at Observe.lhs:182 In the second argument of `send', namely `((return throw) << exc)' In the first argument of `return', namely `(send "throw" ((return throw) << exc) context)' Changing names (of Observable...) does not help, so its is not a name conflict with prelude or libraries The source is avalaible at : http://haskell.cs.yale.edu/hood/downloads/ghc/Observe.lhs (I don't include it here so the M.L. won't be cluttered) If somebody can help, I am completely at a loss Alain

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createAdjustor for Alpha (and Sparc)
by Ken Shan 25 Jul '01

25 Jul '01

Hello again, It seems that I have a registerised GHC mostly working on the Alpha. The main missing piece is createAdjustor. My understanding of (the _ccall rather than _stdcall part of) createAdjustor is as follows: Given "hptr" and "wptr" of types void *hptr; {return type} (*wptr)(void *, void *, {more arguments}); createAdjustor creates "adjustor" of the type {return type} (*adjustor)({more arguments}); such that calling (*adjustor)({argument values}) is equivalent to calling (*wptr)(hptr, {undefined/ignored pointer}, {argument values}). This goal seems difficult to achieve on the Alpha, since its complicated calling convention puts arguments in registers, and we don't know how many arguments there are, let alone how to adjust the stack if needed. But wait! There's a Sparc port of createAdjustor already, and the Sparc passes arguments in registers too! How was that done? I pored over the #ifdef sparc_TARGET_ARCH code in Adjustor.c, and couldn't understand. It puts hptr in %o0 and wptr in %o1, where I assume %o0 is where the first argument is expected in _ccall, but what about shifting over {more arguments}? In any case, given that many architectures pass arguments in registers nowadays, what seems like a more universally workable approach to me is to pass hptr not as a regular function call argument but inside a special register that the called stub function (i.e., *wptr) knows about. This register must be caller-save and must not be involved in the usual prologue sequence generated by gcc. I'd guess that the following would work: i386 %eax alpha $0 = $v0 sparc %g7 This new scheme would involve changing DsForeign.lhs to output different _ccall stub code. Would it work? Any demystification would be greatly appreciated. (By the way, why can't we use $0 and $1 on the Alpha? Only $2 and up are assigned in MachRegs.h.) -- Edit this signature at http://www.digitas.harvard.edu/cgi-bin/ken/sig « ne gâche pas ta vie pour leur idée de patrie » le bouton me dit

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