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Networking : PortNumber
by Thomas L. Bevan 03 Jun '03

03 Jun '03

Hi, How can I take some input and convert this into a PortID ? I don't quite understand why the constructor PortNumber doesn't have the signature PortID = PortNumber Int | ... Instead it is PortID = PortNumber PortNumber where PortNumber is not a member of the Read class. Tom

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a readFile problem
by Naudts, Guido 02 Jun '03

02 Jun '03

Hallo, I have the following problem: my program asks the user for a command, when the command is executed a new command is asked (this is no problem ; an example is in the HUgs distribution namely Main.hs in the Prolog example. However one of the commands is: read filename i.e. read a file and display it. I do not succeed in implementing this. Could anyone give an example of: reading commands in a loop where one of the commands is the read command mentionned above. Or is it not possible in Haskell? I have already wated a lot of time on this, so if anyone gives me an answer I will be very gratefull. Greetings,

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RE: Help: writing ffi bindings to a C library
by Bayley, Alistair 02 Jun '03

02 Jun '03

Yes, I had considered this (writing an abstraction layer in C). I have decided initially to try doing it in Haskell, because I thought that Haskell would be a better choice for writing abstraction layers (not as verbose as C). The idea was to write the Haskell-C bindings at as low a level as possible (i.e. directly to the OCI libraries), and then build up from there. Although the bindings may be ugly, I thought it would have been easier to build higher layers in Haskell rather than C. However, if you think it's probably better to build the first layer in C, then I'll do that. Getting back to my question, can I use functions that take twice-deref'ed pointers as args? This is a function that effectively returns some of its work in "out" arguments e.g. a C function like this: int someCFunction(SomeType **ptrptr, int i) (It would create an opaque structure and point *ptrptr at it. If it fails then it would return a negative value.) Is it simply a case of declaring it like this (in ghc): > data SomeType > type SomeTypeRef = Ptr SomeType > foreign import ccall "blah.h someCFunction" someCFunction :: Ptr SomeTypeRef -> Int -> Int Or must C functions that are to be called from Haskell return results only in the return value? -----Original Message----- From: Ronald Legere [mailto:rjljr2@yahoo.com] Sent: 31 May 2003 15:25 To: Bayley, Alistair; 'haskell-cafe(a)haskell.org' Subject: RE: Help: writing ffi bindings to a C library One strategy is to wrap that funtion in another function (in C) that encapsulates the 'typical' call you want to make. THen import this function into haskell. In any event, start with something simpler, to get the hang of it. Try to write a function (in C) that adds two integers,or prints something and import that in to haskell. There are some examples floating around to get you started, but I can't find them at the moment on the CVS tree. Anyone? Also, read "Tackling the awkward squad" (Google it) Ron --- "Bayley, Alistair" <Alistair_Bayley(a)ldn.invesco.com> wrote: > So... > > I'm still trying to write this Oracle OCI ffi > binding. Can anyone tell me > how to declare the Haskell type for this function: > > sword OCIEnvCreate (OCIEnv **envp, ub4 mode, dvoid > *ctxp, > dvoid *(*malocfp)(dvoid *ctxp, > size_t size), > dvoid *(*ralocfp)(dvoid *ctxp, > dvoid *memptr, size_t > newsize), > void (*mfreefp)(dvoid *ctxp, > dvoid *memptr), > size_t xtramem_sz, dvoid > **usrmempp); > > Note that when I use it, I'm passing 0 (NULL) into > almost all of the args, > so the usage in C is typically: > > rc = OCIEnvCreate(&envhp, OCI_DEFAULT, 0, 0, 0, 0, > 0, 0); > > i.e. I don't care about most of the args, so that > should make the Haskell > declaration simpler. Some of the arguments are > pointers to functions, for > example. > > What I can't figure out is how to declare the type > of the first arg. Is is > Ptr (Ptr OCIEnv) ? > > Here's what I have so far (not much, I know): > > > module Main where > > import Foreign > > import Foreign.C.Types > > import Foreign.C.String > > import Foreign.Ptr > > > data OCIEnv > > > foreign import ccall "oci.h OCIEnvCreate" > ociEnvCreate :: Ptr OCIEnv -> > Int -> Int -> Int -> Int -> Int -> Int -> Int -> Int > ***************************************************************** The information in this email and in any attachments is confidential and intended solely for the attention and use of the named addressee(s). This information may be subject to legal professional or other privilege or may otherwise be protected by work product immunity or other legal rules. It must not be disclosed to any person without our authority. If you are not the intended recipient, or a person responsible for delivering it to the intended recipient, you are not authorised to and must not disclose, copy, distribute, or retain this message or any part of it. *****************************************************************

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How to... use haskell 'functions' in C(++) sources ?
by Antoine Utonium 02 Jun '03

02 Jun '03

Everything is in the title. I like "simplicity" of Haskell and would like to use what i write in my c/c++ programs. Thanks a lot by advance.

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Re: Eval in Haskell
by Lauri Alanko 02 Jun '03

02 Jun '03

[Moving to cafe, this is only barely Haskell-related.] On Sun, Jun 01, 2003 at 04:16:36PM -0700, oleg(a)pobox.com wrote: > Eval of the kind > let x = 1 in eval "x" > is plainly an abomination. I agree, though not because of the optimization issues but rather as a matter of principle: a closed variable should be _closed_, it should not be visible to anything but the body of the let-expression that binds it. And an externally acquired eval-able expression is definitely "anything but". Nevertheless, this abomination is supported even by some scheme implementations: guile> (define local-environment (procedure->syntax (lambda (exp env) env))) guile> (define (eval-where-x-bound exp) ... (let ((x 'foo)) (local-eval exp (local-environment)))) guile> (eval-where-x-bound '(list 'x x)) (x foo) > Incidentally, restricting eval to top-level or "standard" bindings is > not a significant limitation. It is, in general, a very good practice > to apply eval to closed expressions only. This depends entirely on what you want to achive with eval, so I don't think the "in general" is justified. If you just want to evaluate closed expressions whose results are printable and readable, then you really just have an embedded interpreter which happens to read the same language as your source code. On the other hand, it is common for perl programs and especially shell scripts to eval configuration files with the explicit purpose that the configuration file may alter variables which are bound in the main program. For such usage, it is essential that the main program and the evaled file access the same enviroment. (Naturally a configuration file shouldn't be allowed to mess with _everything_ in the main program, but I don't think perl allows detailed adjustment of the bindings in the environment. Some schemes do, though.) Lauri Alanko la(a)iki.fi

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RE: Help: writing ffi bindings to a C library
by Bayley, Alistair 31 May '03

31 May '03

So... I'm still trying to write this Oracle OCI ffi binding. Can anyone tell me how to declare the Haskell type for this function: sword OCIEnvCreate (OCIEnv **envp, ub4 mode, dvoid *ctxp, dvoid *(*malocfp)(dvoid *ctxp, size_t size), dvoid *(*ralocfp)(dvoid *ctxp, dvoid *memptr, size_t newsize), void (*mfreefp)(dvoid *ctxp, dvoid *memptr), size_t xtramem_sz, dvoid **usrmempp); Note that when I use it, I'm passing 0 (NULL) into almost all of the args, so the usage in C is typically: rc = OCIEnvCreate(&envhp, OCI_DEFAULT, 0, 0, 0, 0, 0, 0); i.e. I don't care about most of the args, so that should make the Haskell declaration simpler. Some of the arguments are pointers to functions, for example. What I can't figure out is how to declare the type of the first arg. Is is Ptr (Ptr OCIEnv) ? Here's what I have so far (not much, I know): > module Main where > import Foreign > import Foreign.C.Types > import Foreign.C.String > import Foreign.Ptr > data OCIEnv > foreign import ccall "oci.h OCIEnvCreate" ociEnvCreate :: Ptr OCIEnv -> Int -> Int -> Int -> Int -> Int -> Int -> Int -> Int -----Original Message----- From: Ronald Legere [mailto:rjljr2@yahoo.com] Sent: 21 May 2003 20:32 To: 'haskell-cafe(a)haskell.org' Subject: Re: Help: writing ffi bindings to a C library Agreeing with David, but I like to use types rather than (). YOu can do this because, in ghc, you can write: data Blah with no rhs, and it is understood to be an 'opaque' type. Ghc beleives any claims you make about passing Ptr Blah back and forth to C in your foreign import declarations <* Grin *>. As for passing structures back and forth, and accessing the components, you can do it from Haskell or from the "c-side"... I can send you a sample of doing it from haskell if you wish. Ron --- David Roundy <droundy(a)abridgegame.org> wrote: > On Wed, May 21, 2003 at 04:27:10PM +0100, Bayley, > Alistair wrote: > > construct a Ptr a? What type should "a" be?). > > Unless you actually need to ever access their > contents, I'd just define the > pointers to be of type Ptr (), essentially like a > void * pointer in C. No > need to use Storable if they are only ever accessed > through C functions > (which I would hope would be the case). > -- ***************************************************************** The information in this email and in any attachments is confidential and intended solely for the attention and use of the named addressee(s). This information may be subject to legal professional or other privilege or may otherwise be protected by work product immunity or other legal rules. It must not be disclosed to any person without our authority. If you are not the intended recipient, or a person responsible for delivering it to the intended recipient, you are not authorised to and must not disclose, copy, distribute, or retain this message or any part of it. *****************************************************************

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RE: how to break up a large module?
by Simon Peyton-Jones 30 May '03

30 May '03

A non-exported function can be inlined, and its definition deleted. If there is only one call site, it can be inlined no matter how big it is. S | -----Original Message----- | From: haskell-cafe-admin(a)haskell.org [mailto:haskell-cafe-admin@haskell.org] On Behalf Of Jerzy | Karczmarczuk | Sent: 30 May 2003 14:04 | To: haskell-cafe(a)haskell.org | Subject: Re: how to break up a large module? | | Simon Marlow wrote: | | > Be careful about accidental overloading: | ... | | > Be careful with exports. Prune export lists to just those functions | > which need to be exported. | | | How a too long export list can slow-down the target program? | | Jerzy Karczmarczuk | | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe

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by tony2003＠yahoo.ca 30 May '03

30 May '03

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RE: how to break up a large module?
by Simon Marlow 30 May '03

30 May '03

> I recently spent a couple of hours breaking up a large module > (2.5k lines) > into several smaller modules. When I finally got it working, > I found that > my program took about 60% longer to run. This was running ghc with -O > optimization. > > Any suggestions how to go about breaking up a module in such > a way that it > doesn't slow things down? Do I just have to go adding INLINE > directives to > all my functions? Or is there some other trick I could use? Be careful about accidental overloading: GHC will specialise if it can see the uses of a function within a single module, but not when the function is in another module. Put type signatures on everything, and consider using SPECIALISE pragmas to eliminate overloading. Be careful with exports. Prune export lists to just those functions which need to be exported. Cheers, Simon

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RE: how to break up a large module?
by Simon Peyton-Jones 30 May '03

30 May '03

60% longer is a lot. I'm surprised. I'd try compiling the whole thing both ways with profiling on and see if that reveals anything S | -----Original Message----- | From: haskell-cafe-admin(a)haskell.org [mailto:haskell-cafe-admin@haskell.org] On Behalf Of David | Roundy | Sent: 30 May 2003 13:06 | To: haskell-cafe(a)haskell.org | Subject: how to break up a large module? | | I recently spent a couple of hours breaking up a large module (2.5k lines) | into several smaller modules. When I finally got it working, I found that | my program took about 60% longer to run. This was running ghc with -O | optimization. | | Any suggestions how to go about breaking up a module in such a way that it | doesn't slow things down? Do I just have to go adding INLINE directives to | all my functions? Or is there some other trick I could use? | | For the moment I've reverted to my single big file method, but it certainly | would be handy to be able to break that up so that it wouldn't take so long | to recompile. | -- | David Roundy | http://www.abridgegame.org | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe

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