June 2001 - Glasgow-haskell-users

Fundeps and -fallow-overlapping-instances
by Ashley Yakeley 10 Jun '01

10 Jun '01

My exploration into the more unusual and powerful uses of class fundeps has discovered some curiosities. For instance, consider this: -- class X a instance X Bool instance (Num a) => X a -- For as long as "instance Num Bool" is not declared, the two instances do not de facto overlap. But that's not immediately obvious to GHC, so it will complain, at least by default. But I can stop it complaining by passing -fallow-overlapping-instances, which I interpret as asking GHC to trust me that instances don't overlap. But consider this, with an added dependent argument: -- class X a b | a -> b instance X Bool Bool instance (Num a) => X a Char -- Now GHC will complain even with -fallow-overlapping-instances. This seems inappropriate. So why have the fundep? Well, GHC can still make use of it, and it can still calculate the dependent type: -- class X a b | a -> b where { foo :: a -> b; }; instance X Bool Bool where { foo a = a; }; instance (Num a) => X a Char where { foo a = 'N'; } test = foo True; -- Without the fundep, GHC cannot calculate 'foo True', since 'instance X Bool Bool' is not general enough. This is correct. But with the fundep, GHC will complain that it can't prove that the two instances don't conflict for the fundep, even with -fallow-overlapping-instances. -- Ashley Yakeley, Seattle WA

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resumeThread cannot find the thread! (GHC/HDirect)
by KAKIHARA Norihiro 08 Jun '01

08 Jun '01

I have tried to use FFI on Windows with GHC/HDirect, but the compiled program won't have run: incr.exe: fatal error: resumeThread: thread not found This is my sources and traces. I don't know why such an error has occured (thread, why?). How I force this program to find the thread? (I have made sure `Hello' program can have been compiled normally...) -- SOURCES ------------------------------------- [incr.c] BOOL WINAPI DllMain(args...) { return TRUE; } int __declspec(dllexport) incr(int x) { return x + 1; } [incr.idl] module Incr { [pure]int incr([in]int); } [Main.hs] module Main(main) where main = print (incr 2) -- TRACES --------------------------------------- gcc -mno-cygwin -shared -o incr.dll incr.c -Wl,--out-implib,incr.a ihc incr.idl ghc -fglasgow-exts -package lang -c incr.hs # manually replace `incr@4' into `incr@\NUL\NUL'... # (probably it should be done with .def file :o) ghc -fglasgow-exts -c main.hs ghc -fglasgow-exts -i. -o incr.exe incr.o main.o incr.a -- ENVIRONMENT ----------------------------------- OS : Windows 98 GHC Version : 4.08.2 (Windows InstallShield) with sh.exe in ash-200010425 HDirect Version : 0.60 (Windows InstallShield)

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RE: Ambiguos Types
by Simon Peyton-Jones 08 Jun '01

08 Jun '01

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RE: Empty Datatypes in GHC 5?
by Simon Peyton-Jones 08 Jun '01

08 Jun '01

There isn't such an option at the moment, but it would be simple to add and I've often thoght of doing so. I'm going to be on the train tonight, so you never know... S | -----Original Message----- | From: Ashley Yakeley [mailto:ashley@semantic.org] | Sent: 08 June 2001 01:14 | To: GHC List | Subject: Empty Datatypes in GHC 5? | | | I just joined this list after finally obtaining an i386 | machine primarily | for the purpose of running GHC (I ssh/ftp to it from my Mac). | | A quick question: is there an option to allow empty datatypes in GHC | 5.00? I couldn't see one in the manual. They are useful for type | parameterisation, for instance: | | data Zero; | data Succ n; | | Unfortunately this is contrary to the Haskell Report. | Nevertheless, Hugs | allows it. But GHC, apparently, does not. | | -- | Ashley Yakeley, Seattle WA | | | _______________________________________________ | Glasgow-haskell-users mailing list | Glasgow-haskell-users(a)haskell.org | http://www.haskell.org/mailman/listinfo/glasgow-| haskell-users |

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Empty Datatypes in GHC 5?
by Ashley Yakeley 07 Jun '01

07 Jun '01

I just joined this list after finally obtaining an i386 machine primarily for the purpose of running GHC (I ssh/ftp to it from my Mac). A quick question: is there an option to allow empty datatypes in GHC 5.00? I couldn't see one in the manual. They are useful for type parameterisation, for instance: data Zero; data Succ n; Unfortunately this is contrary to the Haskell Report. Nevertheless, Hugs allows it. But GHC, apparently, does not. -- Ashley Yakeley, Seattle WA

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RE: [GHC5] Creating Socket.PortNumber from Int?
by Simon Marlow 07 Jun '01

07 Jun '01

> Wed, 6 Jun 2001 10:17:34 +0100, Simon Marlow > <simonmar(a)microsoft.com> pisze: > > > Think of it this way: mkPortNumber has been renamed to > fromIntegral, and > > now supports making port numbers from any integral type, > not just Int. > > BTW, why PortNumber is not just Int? It's kept in network byte order. We could make it an Int and do the translation to/from network byte order whenever we need to pass one outside Haskell - I didn't investigate doing it this way, it may or may not be simpler. Cheers, Simon

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Ambiguos Types
by Saswat Anand 07 Jun '01

07 Jun '01

Hi, I have 2 questions: 1- When I load the following module: module Foo() where default (Float) into ghci. 2+3 gives (5::Integer). Should it not give (5.0::Float). Hugs does. 2. class Op a where (%+) :: a -> a -> a instance Op Integer where (%+) = (+) with the above code: (2 %+ 3) should be resolved to Integer type. Could anybody explain why it should not. Thanks, S

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Re: [GHC5] Creating Socket.PortNumber from Int?
by Marcin 'Qrczak' Kowalczyk 06 Jun '01

06 Jun '01

Wed, 6 Jun 2001 10:17:34 +0100, Simon Marlow <simonmar(a)microsoft.com> pisze: > Think of it this way: mkPortNumber has been renamed to fromIntegral, and > now supports making port numbers from any integral type, not just Int. BTW, why PortNumber is not just Int? -- __("< Marcin Kowalczyk * qrczak(a)knm.org.pl http://qrczak.ids.net.pl/ \__/ ^^ SYGNATURA ZASTÊPCZA QRCZAK

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RE: size of interpreted code
by Simon Marlow 06 Jun '01

06 Jun '01

> With ghc-5.00.1, > the compiled Foo.a, Foo.o are each of 7Mb, > ghci -package foo ... > Prelude> :l T_ > loads the interpreted demo examples (importing Foo.o), > and this needs more than 45Mb heap. As we've mentioned before, GHCi has some memory leaks. This is on the list of things to investigate, but we haven't got around to it yet. Cheers, Simon

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size of interpreted code
by S.D.Mechveliani 06 Jun '01

06 Jun '01

Dear ghc-5.00.1, I wonder: is the interpreted code generally expected to be larger than compiled to .o ? I have certain Foo project which under ghc-4.08 had: compiled Foo + compiled demo examples make Foo-Demo.a of 10Mb, and this all load and run on 32Mb RAM computer inside RAM (probably, 15Mb will remain for heap). With ghc-5.00.1, the compiled Foo.a, Foo.o are each of 7Mb, ghci -package foo ... Prelude> :l T_ loads the interpreted demo examples (importing Foo.o), and this needs more than 45Mb heap. Recalling that ghci does not like strict polymorphic data fields, I add that the compiled part has the strict polymorphic fields like D !a !(a -> a), but the interpreted demo programs do not have strict fields. ----------------- Serge Mechveliani mechvel(a)botik.ru

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