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How do I create an IOError exception?
by Bayley, Alistair 04 Jun '03

04 Jun '03

(I know I'm asking some noddy questions, but hey, that's what this list is for...) How do I create IOError exceptions? System.IO.Error has two functions that create IOErrors: userError and mkIOError. However, both of them take a String (I assume containing a description of the problem), and mkIOError takes optional Handle and FilePath args. http://www.haskell.org/ghc/docs/latest/html/base/System.IO.Error.html What I'd like to do is stuff some more information into the exception (a bit like Java exceptions), along the lines of: > mkIOError :: a -> IOError where I could choose to use it like this (ociHandleAlloc is a foreign C function): > handleAlloc2 handleType env ptr = do > rc <- ociHandleAlloc env ptr handleType 0 0 > if rc < 0 > then ioError (mkIOError ("Couldn't allocate handle", rc)) > else peek ptr When I catch the exception (currently in main) I would like to interrogate it to get the values I stuffed in it (in this case a (String, Int) tuple), and then do some error reporting by calling another function which decodes the error number. Is this the wrong way to go about error handling? Or is it relatively simple to create your own IOErrors? Have I missed something in the docs? ***************************************************************** 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: Help: writing ffi bindings to a C library
by Bayley, Alistair 04 Jun '03

04 Jun '03

Thanks. This is very helpful. I'm making much better progress now. Is alloca the idiomatic technique when you want to create a pointer to a pointer? Or are there other ways? Initially I tried to pass a Ptr (Ptr SomeType), but I couldn't because Ptr has no constructors To create values of type Ptr I must use the functions in Foreign.Marshal.Alloc (and Foreign.Marshal.Utils). Correct? -----Original Message----- From: Marcin 'Qrczak' Kowalczyk [mailto:qrczak@knm.org.pl] Sent: 02 June 2003 10:46 To: haskell-cafe(a)haskell.org Subject: Re: Help: writing ffi bindings to a C library Dnia pon 2. czerwca 2003 09:58, Bayley, Alistair napisał: > 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). You can write it in Haskell too and I would recommend that - unless the C library uses some passing convention Haskell cannot handle (e.g. passing structs by value, or having variable argument count, or relying heavily on macros). > 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 Sure. You can use libraries documented in the Haskell FFI proposal. > 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 foreign import ccall "blah.h someCFunction" someCFunction :: Ptr SomeTypeRef -> CInt -> IO CInt haskellWrapper :: Int -> IO (Maybe SomeTypeRef) haskellWrapper arg = alloca $ \ptr -> do res <- someCFunction ptr (fromIntegral arg) if res < 0 then return Nothing else liftM Just (peek ptr) You can raise an IO error instead. You can wrap the result in a ForeignPtr if it should be finalized when it's garbage collected. You can use hsc2hs to access integer constants, enumeration values and structs from Haskell, or write C wrappers inline inside Haskell source (e.g. to turn macros into functions). -- __("< Marcin Kowalczyk \__/ qrczak(a)knm.org.pl ^^ http://qrnik.knm.org.pl/~qrczak/ _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ***************************************************************** 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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Network.CGI
by Thomas L. Bevan 04 Jun '03

04 Jun '03

Can anyone point me to some documentation on the Network.CGI package? The wrapper fn is clear enough but I'm not sure what pwrapper is for or the nature of the contract in connectToCGIScript Tom

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Please help me
by David Savimbi 03 Jun '03

03 Jun '03

From: David Jonas Savimbi Johannesburg, South Africa Email: djsavimbi(a)phantomemail.com June 3rd, 2003. Dear Sir, It is my humble pleasure to write you this letter irrespective of the fact that you do not know me. However, I got your name through your country business directory here in my search for a reliable and trustworthy person that can assist me confidently. My name is Mr.John Jonas Savimbi. I am the son of Late Dr. Jonas Savimbi from Angola. I am 29 years old and I have got two younger sisters of same blood. Our mother died almost a year ago. We are all fighting for political asylum in South Africa. We cannot find a home in Angola anymore because of the war that our late father fought with the government of Angola until he died in that war. The government of Angola is now mad at us because our late father also wanted to be president and caused the people to fight the war for him because he was the president of UNITA political movement of Angola. So now we are in South Africa and we are suffering too much because we don't have money and the government of South Africa will not give jobs to asylum seekers. I am much concerned about my younger sisters who are finding it very difficult to manage in the situation. But I know that we should not suffer this way. I know that I must not let my younger sisters get into trouble because of money. So after consideration I am hereby begging for your assistance to help me to recover the sum of USD $29 Million which is my inheritance from my late mother. My late mother had taken this money with her to Spain in a diplomatic metal box marked (Precious Stones). Subsequently she lodged the metal box (As precious Stones) with a Securities and Valuables Protection company in Spain. I am supposed to be the beneficiary in the event of her death. However, all effort I made to go Spain to claim was refused by the Spainish embassy. And this was while it was still possible for me to travel. Now I cannot travel anywhere anymore. So in the situation that we are facing now, I must find somebody who can go to the Spain on my behalf. I understand that I will have to transfer my beneficiary rights unto you. I am willing to do so in the hope that you are a God fearing person who will not abandon us after you have the money. So from the bottom of my heart I am giving you 20% of the all the money. Once we have enough to sustain us sufficiently, you may be come our fund manager and invest the rest wisely for us. If you will be kind to assist us, please inform me urgently. Kind regards to you and your family. Sincerely, David Jonas savimbi

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Please help me
by David Savimbi 03 Jun '03

03 Jun '03

From: David Jonas Savimbi Johannesburg, South Africa Email: djsavimbi(a)phantomemail.com June 3rd, 2003. Dear Sir, It is my humble pleasure to write you this letter irrespective of the fact that you do not know me. However, I got your name through your country business directory here in my search for a reliable and trustworthy person that can assist me confidently. My name is Mr.John Jonas Savimbi. I am the son of Late Dr. Jonas Savimbi from Angola. I am 29 years old and I have got two younger sisters of same blood. Our mother died almost a year ago. We are all fighting for political asylum in South Africa. We cannot find a home in Angola anymore because of the war that our late father fought with the government of Angola until he died in that war. The government of Angola is now mad at us because our late father also wanted to be president and caused the people to fight the war for him because he was the president of UNITA political movement of Angola. So now we are in South Africa and we are suffering too much because we don't have money and the government of South Africa will not give jobs to asylum seekers. I am much concerned about my younger sisters who are finding it very difficult to manage in the situation. But I know that we should not suffer this way. I know that I must not let my younger sisters get into trouble because of money. So after consideration I am hereby begging for your assistance to help me to recover the sum of USD $29 Million which is my inheritance from my late mother. My late mother had taken this money with her to Spain in a diplomatic metal box marked (Precious Stones). Subsequently she lodged the metal box (As precious Stones) with a Securities and Valuables Protection company in Spain. I am supposed to be the beneficiary in the event of her death. However, all effort I made to go Spain to claim was refused by the Spainish embassy. And this was while it was still possible for me to travel. Now I cannot travel anywhere anymore. So in the situation that we are facing now, I must find somebody who can go to the Spain on my behalf. I understand that I will have to transfer my beneficiary rights unto you. I am willing to do so in the hope that you are a God fearing person who will not abandon us after you have the money. So from the bottom of my heart I am giving you 20% of the all the money. Once we have enough to sustain us sufficiently, you may be come our fund manager and invest the rest wisely for us. If you will be kind to assist us, please inform me urgently. Kind regards to you and your family. Sincerely, David Jonas savimbi

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RE: Networking : PortNumber
by Simon Marlow 03 Jun '03

03 Jun '03

> Sorry, > > I've just worked it out. > > PortNumber is an instance of the class Enum > so we can use > > toEnum :: Int -> a It's also an instance of the Integral class, which means you can just write integral constants of type PortNumber. eg. (80 :: PortNumber) is valid. Also, the universal integral conversion function 'fromIntegral' can be used for converting values of other integral types into PortNumbers (this is preferable to toEnum). Cheers, Simon

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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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