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GHC non-standard interface file location problem
by Bernd Holzmüller 05 Apr '01

05 Apr '01

Hi all, while compiling a file select.hs ghc said: select.hs:1: Could not find interface file for `Concurrent' in the directories ./*.hi c:/programme/haskell/ghc-4.08/lib/imports/std/*.hi can someone tell me why ghc does not find the interface files for the concurrency library (or any of the other non-standard libraries) or how to tell ghc, where this library sits? Is there any GHC INCLUDE path to be set? I am using ghc 4.08 on a Windows NT machine. Thanks, Bernd Holzmüller

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Hard earned hints for using Win32 GHC 4.08.2 and HDirect.
by Mike Thomas 04 Apr '01

04 Apr '01

Hi all. I thought I might share some hints on making HDirect work with GHC 4.08.2. Installing and checking GHC: - Get the installer from the GHC downloads page, do the installation per the instructions there, including Cygwin etc. - Remove the digit "1" from the bottom of lib/imports/win32/Win32.hi - Remove old .hi files from any program source directories you may have. - To test, try compiling the Windows hello.lhs example using the command line "ghc hello.lhs -o hello.exe -package win32" and run hello.exe. - If you get linker errors about "import____timezone_dll" from time.o, you need to add the line: push(@SysLibrary, '-lcrtdll') if ($TargetPlatform =~ /-(mingw32|cygwin32)$/); below the line: push(@SysLibrary, '-lwsock32') if ($TargetPlatform =~ /-(mingw32|cygwin32)$/); in your "bin/ghc" driver script. This is because the distribution is built with an old version of Cygwin GCC which links against crtdll.dll rather than msvcrt.dll when -mno-cygwin is set on the command line (GHC uses mingw32). By doing this, spare symbols are resolved after linkage with msvcrt.dll. DO NOT SUBSTITUTE -lmsvcrt with -lcrtdll. If you substitute, you will get errors about running out of resources on fileOpen at run time. - You may also need to update your GCC Mingw32 libraries and headers from the Sourceforge Mingw32 downloads page if you have unexplained crashes. Building HDIrect 0.17 - Uninstall previous versions of HDirect including "lib/imports/com" and associated libraries, which don't work very well with GHC 4.08.2. - Get the source from the HDirect web site and untar it somewhere. - You may need to edit "lib/WideStringSrc.c" if you use the latest Cygwin distribution to remove a clashing definition and declaration of wcslen(). - Build per the instructions in the INSTALL file. - This gives you a bare bones ihc.exe which cannot handle type libraries. - Install the freshly built lib/*.hi files in a new ghc "lib/imports/com" directory and also the libraries (libHScom.a, libhdirect.a) into ghc's "lib" directory. - Do "make clean", deleting "src/ihc.exe" by hand. - Set SUPPORT_TYPELIBS=YES in "src/Makefile" - "make boot", "make", then "make lib" as before. - You now have version 0.17 of HDirect for Windows. Question Time: Why does ihc ignore binary interfaces in type libraries such as dx7vb.dll? Cheers Mike Thomas

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type error. reply
by S.D.Mechveliani 04 Apr '01

04 Apr '01

Norman Ramsey <nr(a)eecs.harvard.edu> writes > [..] > class Formula f where > eval :: f a -> Environment a -> Bool > [..] > type Environment a = Var -> a > type Var = String > [..] > data Formula f => Row a = Row (f a, Weight) > type Weight = Float > > Hugs rejects this program: [ .. ] Maybe, the contexts are not needed in the data declarations. I would write in your case something like data Row f a = Row (f a, Weight) and then, define the same instances as the initially intended to define for Row: instance (Context1 f a) => Foo1 (Row f a) where ... instance (Context2 f a) => Foo2 (Row f a) where ... ... But there arises a question: as the instances define what is allowed to do with the data type under various conditions on its parameters, then why at all the language allows the `data' contexts? ----------------- Serge Mechveliani mechvel(a)botik.ru

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FSm canonical in HASKELL
by luc 04 Apr '01

04 Apr '01

are there some cannonical way to implement FSM in haskell ? anything funny with combinators ? erlang got some, but relying on message passing. for Tab : state SA->state SB, T bc : state SB->state SC SA()-> receive Tab -> SB() end. SB()->receive Tbc->SC() end. any way to avoid declaring state as Type ? ie some kind of generic state machine ?

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help wanted with type error message
by Norman Ramsey 04 Apr '01

04 Apr '01

I'm learning Haskell, and I'm having trouble understanding the meaning of a `context' as applied to the declaration of an algebraic datatype. I would like to say the following: A formula is a predicate over environments. > class Formula f where > eval :: f a -> Environment a -> Bool -- evaluate the formula > eq :: Var -> a -> f a -- basic equality > (&) :: f a -> f a -> f a -- conjunction > type Environment a = Var -> a > type Var = String A row has a formula and a weight. > data Formula f => Row a = Row (f a, Weight) > type Weight = Float Hugs rejects this program: ERROR "hard.lhs" (line 14): Undefined type variable "f" Line 14 is the definition of Row. Can anyone explain the proper use of a context in a data definition? Thanks, Norman

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Libraries for multipart MIME encoding/decoding?
by Tom Moertel 03 Apr '01

03 Apr '01

Before I rush off and reinvent another wheel, does anybody know of a Haskell library to perform MIME encoding and decoding (a la IETF RFC 2045)? I'd like to be able to decode and process binary files submitted via HTTP POST, and so I need multipart support. The CGI libraries listed on www.haskell.org don't seem to offer this, hence my request. Thanks for any pointers or advice you may be able to provide. Cheers, Tom

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thanks both of you!
by MikeKn22＠aol.com 03 Apr '01

03 Apr '01

Just wanted to address both responses I got back: Dominic, That syntax looks a lot better. Sorry I have been a Haskell programmer for like 8 hours ;) Thanks for the tip. I am learning how one can use many functions in one line. Christian, Sorry all code didn't get sent, but I think you nailed it right on the head. I don't need do and monads in findToken. I rewrote it like this: findToken :: [String] -> [String] findToken st = tail (findName st) and it works fine. Thanks a million. Could you briefly describe to me when do and monads should be used? My hunch is mostly when you deal with IO is this correct? Sorry all for asking trivial questions, but we all have to start soemwhere I guess. Thanks for all the help! I am beginning to like Haskell more and more. I am mostly a C++ programmer, but am taking a class where we are introducted to Prolog and Haskell so we get to see how different languages can be from each other. My problem is am still stuck in that stinking imperative mode of though ;) I am glad though I am expanding my ways of seeing things. Thanks to all again. Rob

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Help with code
by MikeKn22＠aol.com 03 Apr '01

03 Apr '01

I thank everyone who answered my last question. I think I am making progress. My new problem really has me confused. I guess it is because I am new to the language. To make this wode run, put the .txt file in under c:/ and then load the .hs file in hugs98. After that you can type the comman testReadFile at the main prompt. The result is: ["","assign","","int>",""] which seems all wrong to me since it is returning the tail of each string in my string list. When I just want the tail of the string list itself which should be ["<assign>","=","<int>","3"] The same type of thing happen when I tried returning the head of the list in which I believe the string "x<=<3" was returned when only "x" should have been retured. Any ideas why head and tail are acting on each string of my string list rather then the string list itself? Thanks much in advance. Rob

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RE: recip for Ratio
by Simon Peyton-Jones 03 Apr '01

03 Apr '01

Folks, I'm finally getting back to revising the Haskell 98 report, you'll be glad to hear. So I'll be emitting a few consultative messages. This is the first. Scott Turner points out: | In the Haskell 98 Library Report, recip is defined for the | Ratio type as: | recip (x:%y) = if x < 0 then (-y) :% (-x) else y :% x | | Is it intentional that | recip (0 % 1) | is not an error? Everywhere else the denominator is forced | to be positive. Infinity can be a useful number, if the type | is consistent about it. He's right. Everywhere else in the Ratio library we use '%' to construct rationals, a smart constructor that enforces the invariant that the denominator is positive and nonzero, and the numerator and denominator have no common divisor. It seems that the above specification for recip is guilty of premature optimisation. We should instead define it as recip (x :% y) = y % x leaving the smart constructor to enforce the invariant. An implementation might optimise this, knowing that x and y have no common divisor, but that is not the role of a specification. Any objections to this change? Simon

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A Hugs bytecode interpreter
by Tore Lund 03 Apr '01

03 Apr '01

Hugs is a neat system, but the very idea of compiling from source code each time you run a program makes Hugs unsuited for many purposes. So my question is, has anyone tried to rearrange the components of Hugs into a bytecode compiler plus runtime? And if not, maybe the Hugs maintainers had a word of advice on how to go about this? There is nch98, of course, but it is somewhat bulky for the purposes I have in mind. I am looking for something small that would compile to 16-bit code that would run in 64K code + 64K data. The raw material for such a system is probably present in Hugs, but what's the best way to extract it with a minimum of fuss? Grateful for any hint. -- Tore

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