- Glasgow-haskell-users

RE: help needed for adding isWHNF primop to 5.00.2
by Simon Marlow 31 Jul '01

31 Jul '01

> I wonder if Andy is reading this? Possibly there are other people > around who are also interested in this. I think the HAT people > at NHC headquarters are also interested in these things. There > once was talk of starting a debugging group for Haskell, but I > don't know what happened. There's a mailing list for debugger-related discussion at debuggers(a)haskell.org (subscribe in the usual way). To date it has received a single message, namely the nhc 1.06 announcement :-) Cheers, Simon

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RE: help needed for adding isWHNF primop to 5.00.2
by Simon Marlow 31 Jul '01

31 Jul '01

> Tue, 31 Jul 2001 12:38:03 +0100, Simon Marlow > <simonmar(a)microsoft.com> pisze: > > > That's the way I'd go. You have to declare the primitive like this, > > BTW: > > > > isWHNF# :: a -> (# State# RealWorld, Int# #) > > > > because the compiler doesn't know about the IO type and you > can't return > > a Bool directly. > > It can return a Bool, e.g. ==# returns a Bool. But ==# doesn't also return an unboxed tuple, and the code generator has special hacks to deal with primops that return enumerated types. The ==# primop actually returns an Int# which the code generator arranges to convert into a real Bool using the closure table. I guess you could return a Bool by actually indexing into the closure table, or by just returning {False,True}_static_closure. Cheers, Simon

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Re: help needed for adding isWHNF primop to 5.00.2
by Marcin 'Qrczak' Kowalczyk 31 Jul '01

31 Jul '01

Tue, 31 Jul 2001 12:38:03 +0100, Simon Marlow <simonmar(a)microsoft.com> pisze: > That's the way I'd go. You have to declare the primitive like this, > BTW: > > isWHNF# :: a -> (# State# RealWorld, Int# #) > > because the compiler doesn't know about the IO type and you can't return > a Bool directly. It can return a Bool, e.g. ==# returns a Bool. -- __("< Marcin Kowalczyk * qrczak(a)knm.org.pl http://qrczak.ids.net.pl/ \__/ ^^ SYGNATURA ZASTÊPCZA QRCZAK

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RE: help needed for adding isWHNF primop to 5.00.2
by Simon Marlow 31 Jul '01

31 Jul '01

> From reading the documentation that comes with GHC and > glancing over the > source code, I came to these set of assumptions, please > correct me if I am > wrong: > > - values of unpointed types are never in WHNF That's really up to you, but the normal definition of WHNF applies only to types containing _|_, i.e. pointed types. Unpointed types are never represented by thunks, so I would be inclined to include them in WHNF. > - values of pointed types may be in WHNF, in particular: > > - data constructors are in WHNF > - partial applications are in WHNF > - functions are in WHNF > - thunks are not in WHNF > (this list is probably not exhaustive as you say, but > I am happy > with this set of definitions for the moment) You also have to deal with indirections, although you can assume (at the moment) that an indirection will eventually lead to an object in WHNF. > > I can also imagine it > > could interact badly with the complexities of GHC's > > simplifer. > > This is something I do not know. In the end I may define it > with this type: > > isWHNF :: a -> IO Bool That's the way I'd go. You have to declare the primitive like this, BTW: isWHNF# :: a -> (# State# RealWorld, Int# #) because the compiler doesn't know about the IO type and you can't return a Bool directly. There's no problem with the simplifier as long as you declare the primitive to have the correct properties, i.e. that the polymorphic argument is lazy. > I want it for the purposes of meta-programming, and also for > debugging since > that is what I am working on. At the end of a computation > (that results in > a value of pointed type, say) I want to know to what extent > expressions were > evaluated: > > foo xs = take 3 xs > > ... foo [4..] ... > > debugger> foo [4,5,6,_ = [4,5,6] It sounds like you also need a way to take apart arbitrary objects and look at their components. I know that Andy Gill was also interested in having similar facilities, perhaps he can help out. Cheers, Simon

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RE: help needed for adding isWHNF primop to 5.00.2
by Julian Seward (Intl Vendor) 31 Jul '01

31 Jul '01

| > I would like to add a primitive to GHC 5.00.2 of the form: | > | > isWHNF :: a -> Bool One might be inclined to ask what for? Such a primitive is probably difficult to implement, given the variety of GHC's closures, and is potentially dangerous -- you could conceivably break referential transparency (?) I can also imagine it could interact badly with the complexities of GHC's simplifer. What would you hope to gain from such a thing? Perhaps you have some wider purpose which could be achieved some other way? J

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RE: linking with c++ libraries
by Julian Seward (Intl Vendor) 30 Jul '01

30 Jul '01

| To reliably link with C++, you need to compile both the code | which invokes C++ (i.e. whatever uses the C++ library) and | "main" (that is, ghc/rts/Main.c, not main.hs) with a C++ compiler. | | So, in summary: | | - Compile any code which may call the C++ library (and keep | inter-module inlining in mind; probably safest to compile | all of your code this way) via C, and compile the C with g++. | | - Re-compile the run-time system (at least Main.c) with | g++, too. | | That may not fix your specific core dump, but you'll need to | do this anyway. After some discussion in the GHC office, we're unsure about why you need to compile Main.c with a C++ compiler for this to work. Pls can you clarify? J

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outputs during runtime
by Nicole Gabler 30 Jul '01

30 Jul '01

Hello All, I wrote a small haskell program that amongst other things parses some files to manipulate them. During runtime I want the program to output information about the status every time another file is parsed. That doesn't work, the output appears much later, mostly not until end of program. But I need these outputs at that specific time, so what can I do to manage it? Thanks Nicole

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RE: outputs during runtime
by Julian Seward (Intl Vendor) 30 Jul '01

30 Jul '01

Unfortunately that usually means that you need to let the IO type filter down from the top level to all fns which need to print something. Then you can emit a message perhaps in the same function which reads the files. Or is it perhaps a buffering problem? J -----Original Message----- From: Nicole Gabler [mailto:gabler@ics-ag.de] Sent: Monday, July 30, 2001 10:50 AM To: glasgow-haskell-users(a)haskell.org Subject: outputs during runtime Hello All, I wrote a small haskell program that amongst other things parses some files to manipulate them. During runtime I want the program to output information about the status every time another file is parsed. That doesn't work, the output appears much later, mostly not until end of program. But I need these outputs at that specific time, so what can I do to manage it? Thanks Nicole

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Re: Rationals
by Sigbjorn Finne 30 Jul '01

30 Jul '01

Amanda Clare ajc(a)aber.ac.uk writes: > > 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. As you noticed, you need to import Ratio to get at % -- GHC gets this right wrt the Haskell98 report. Hugs exports it from the Prelude (as does NHC, by the looks of it), which used to be right, but isn't in H98. This could be trivially fixed on the Hugs side, but I'm not sure the resulting breakage would be worth it. > The Haskell98 report says: > "In particular, the type Rational is a ratio of two Integer values, as > defined in the Rational library." That's a typo in the Report, it should say the "Ratio library" (Section 6.4, Simon). --sigbjorn

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RE: help needed for adding isWHNF primop to 5.00.2
by Simon Marlow 30 Jul '01

30 Jul '01

> Hi GHC people, > > I would like to add a primitive to GHC 5.00.2 of the form: > > isWHNF :: a -> Bool > > I was able to do (something like) this a while ago in 4.06, > but have got > stuck trying to do the same with 5.00.2. One problem is that you didn't call it 'reallyUnsafeIsWHNF#' :-) (or you could give it an IO type, to follow the current trend). Simon

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