- Beginners - Haskell.org

Allowing multiple FDs with createProcess
by Swaren 14 Feb '26

14 Feb '26

Hi! I'm new to Haskell, and I have a problem with the `createProcess` function (used to spawn a new Unix process) and FDs. The function takes a `CreateProcess` data structure, which contains `std_in`, `std_err` and `std_out`, plus other unrelated parameters. These std parameters allow to give specific file descriptors to the child process (0, 1 and 2, which are the standard std FDs). This feature allows to capture the output of processes, or provide them input, by giving them a pipe as std_in and std_out, for example. Now, is there a way to define other file descriptors? Like, having 5 more input pipes for the process to use. Currently, the `CreateProcess` API seems to be limited to the first three FDs. I could disable the `close_fds` arg of `CreateProcess`, so that all the FDs are given to the process, but that's not truly a solution as it allows the process to access other FDs of my program. Maybe there's a library for that, tell me, but I'd like to keep it the most "native" / built-in as possible. (plus, for some reason, it would be a pain to install a proper Haskell toolchain on my Frankenstein-like Linux machine) Hope it's clear enough, thanks!

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Noob List Woes
by Duke Normandin 18 Dec '25

18 Dec '25

Just started learning Haskell! Currently watching this particular video: https://youtu.be/vhsONvQc-Dc?list=PLmTgnNwroyn8TnF26YRvW-hvQF1ypztzg in the seies. I copied his code verbatim, but keep getting errors running the code on my antiX-23.2 Linux box using a fresh Haskell install. [quote] main = do let testScores = [79,85,92,56] print (testScores !! 0) -- !! means index-of print (testScores !! 3) -- last item print (head testScores) -- returns first item in a list [/quote] [quote] runghc "hello.hs" (in directory: /home/dnormandin/Programming/haskell/code) hello.hs:1:8: error: [GHC-52095] Unexpected do block in function application: do let testScores = ... Suggested fixes: • Use parentheses. • Perhaps you intended to use BlockArguments You may enable this language extension in GHCi with: :set -XBlockArguments | 1 | main = do | ^^... Compilation failed. [/quote] I can't figure out what's wrong with the code. I _think_ that the indenting is ok - which BTW is a bloody PITA!! I have some cl/scheme experience, but mostly with procedural langs. Maybe the tutorial is too dated to be useful? If it is, is there a similar video tutorial for beginners? TIA ... -- Duke

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TargirDotCom
by walid falcon 08 Aug '25

08 Aug '25

https://www.targir.com/

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شهادة الأبوة في المغرب
by walid falcon 08 Aug '25

08 Aug '25

Spam detection software, running on the system "mail.haskell.org", has identified this incoming email as possible spam. The original message has been attached to this so you can view it (if it isn't spam) or label similar future email. If you have any questions, see @@CONTACT_ADDRESS@@ for details. Content preview: ÙÙ ÙØ§ ØªØØªØ§Ø¬ ÙØ¹Ø±ÙØªÙ ØÙÙ Ø´ÙØ§Ø¯Ø© Ø§ÙØ£Ø¨ÙØ© Ø¨Ø§ÙÙØºØ±Ø¨ ÙÙÙÙÙ ØªØÙÙÙ Ø§ÙØ·ÙØ¨ ÙÙ Ø®ÙØ§Ù Ø§ÙØ±Ø§Ø¨Ø· Ø§ÙÙØ¨Ø§Ø´Ø± https://www.targir.com/2025/04/blog-post_14.html [...] Content analysis details: (6.6 points, 5.0 required) pts rule name description ---- ---------------------- -------------------------------------------------- 0.0 FREEMAIL_FROM Sender email is commonly abused enduser mail provider (pikolasikolatest2[at]gmail.com) -0.0 SPF_PASS SPF: sender matches SPF record 0.1 FREEMAIL_ENVFROM_END_DIGIT Envelope-from freemail username ends in digit (pikolasikolatest2[at]gmail.com) 5.0 UNWANTED_LANGUAGE_BODY BODY: Message written in an undesired language 0.0 HTML_MESSAGE BODY: HTML included in message 1.5 BODY_8BITS BODY: Body includes 8 consecutive 8-bit characters 0.0 T_DKIM_INVALID DKIM-Signature header exists but is not valid 0.0 T_TO_NO_BRKTS_FREEMAIL T_TO_NO_BRKTS_FREEMAIL The original message was not completely plain text, and may be unsafe to open with some email clients; in particular, it may contain a virus, or confirm that your address can receive spam. If you wish to view it, it may be safer to save it to a file and open it with an editor.

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Utrecht Summer School on Advanced Functional Programming
by Wouter Swierstra 01 May '25

01 May '25

# Second Call for Participation SUMMER SCHOOL ON ADVANCED FUNCTIONAL PROGRAMMING Utrecht, the Netherlands, 07 July – 11 July 2025 http://afp.school **Please register before June 15th** ## ABOUT The Advanced Functional Programming summer school has been running for more than fifteen years. We aim to educate aspiring Haskell programmers beyond the basic material covered by many textbooks. The lectures will cover several more advanced topics regarding the theory and practice of Haskell programming, including topics such as: * lambda calculus; * lazy evaluation; * generalized algebraic data types; * type families and type-level programming; * concurrency and parallelism. The summer school will be held in Utrecht and consists of a mix of lectures, labs, and a busy social program. ## PREREQUISITES We expect students to have a basic familiarity with Haskell already. You should be able to write recursive functions over algebraic data types, such as lists and trees. There is a great deal of material readily available that covers this material. If you've already started learning Haskell and are looking to take your functional programming skills to the next level, this is the course for you. ## DATES Registration deadline: June 15th, 2025 School: 07 July – 11 July 2025 ## COSTS € 950 euro - Profession registration fee € 500 euro - Student registration fee € 200 euro - Housing fee We will charge a registration fee of €950 (or €500 for students) to cover our expenses. This fee includes all lunches, dinners, and coffee breaks - you won't need to budget much else besides your travel. If this is problematic for you for any reason at all, please email the organisers and we can try to offer you a discounted rate or a fee waiver. We have a limited number of scholarships or discounts available for students that would not be able to attend otherwise, especially for women and under-represented minorities. ## FURTHER INFORMATION Further information, including instructions on how to register, is available on our website: http://afp.school

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help
by Timothy Xu 23 Mar '25

23 Mar '25

help > Le 21 mars 2025 à 10:33, beginners-request(a)haskell.org a écrit : > > Send Beginners mailing list submissions to > beginners(a)haskell.org > > To subscribe or unsubscribe via the World Wide Web, visit > https://urldefense.proofpoint.com/v2/url?u=http-3A__mail.haskell.org_cgi-2D… > or, via email, send a message with subject or body 'help' to > beginners-request(a)haskell.org > > You can reach the person managing the list at > beginners-owner(a)haskell.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Beginners digest..." > > > Today's Topics: > > 1. Utrecht Summer School on Advanced Functional Programming > (Wouter Swierstra) > 2. Re: Utrecht Summer School on Advanced Functional Programming > (Vinod Parthasarathy) > 3. Re: Utrecht Summer School on Advanced Functional Programming > (Wouter Swierstra) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Thu, 20 Mar 2025 16:59:13 +0100 > From: Wouter Swierstra <w.s.swierstra(a)uu.nl> > To: beginners(a)haskell.org > Subject: [Haskell-beginners] Utrecht Summer School on Advanced > Functional Programming > Message-ID: <32bfd4d7-034c-4529-9bfc-b51efb1eb074(a)uu.nl> > Content-Type: text/plain; charset=UTF-8 > > > # Call for Participation > > SUMMER SCHOOL ON ADVANCED FUNCTIONAL PROGRAMMING > > Utrecht, the Netherlands, 07 July – 11 July 2025 > > https://urldefense.proofpoint.com/v2/url?u=http-3A__www.afp.school_&d=DwIGa… > > **Please register before June 15th ** > > ## ABOUT > > The Advanced Functional Programming summer school has been running for > more than fifteen years. We aim to educate aspiring Haskell programmers > beyond the basic material covered by many textbooks. > > The lectures will cover several more advanced topics regarding the > theory and practice of Haskell programming, including topics such as: > > * lambda calculus; > * lazy evaluation; > * generalized algebraic data types; > * type families and type-level programming; > * concurrency and parallelism. > > The summer school will be held in Utrecht and consists of a mix of > lectures, labs, and a busy social program. > > ## PREREQUISITES > > We expect students to have a basic familiarity with Haskell > already. You should be able to write recursive functions over > algebraic data types, such as lists and trees. There is a great deal > of material readily available that covers this material. If you've > already started learning Haskell and are looking to take your > functional programming skills to the next level, this is the course > for you. > > ## DATES > > Registration deadline: June 15th, 2025 > School: 07 July – 11 July 2025 > > ## COSTS > > € 950 euro - Profession registration fee > € 500 euro - Student registration fee > € 200 euro - Housing fee > > We will charge a registration fee of €950 (or €500 for students) to > cover our expenses. This fee includes all lunches, dinners, and coffee > breaks - you won't need to budget much else besides your travel. > > If this is problematic for you for any reason at all, please email the > organisers and we can try to offer you a discounted rate or a fee > waiver. We have a limited number of scholarships or discounts available > for students that would not be able to attend otherwise, especially for > women and under-represented minorities. > > ## FURTHER INFORMATION > > Further information, including instructions on how to register, is > available on our website: > > https://urldefense.proofpoint.com/v2/url?u=http-3A__afp.school_&d=DwIGaQ&c=… > > > ------------------------------ > > Message: 2 > Date: Fri, 21 Mar 2025 09:26:26 +0530 > From: Vinod Parthasarathy <vinnytryclyst(a)gmail.com> > To: The Haskell-Beginners Mailing List - Discussion of primarily > beginner-level topics related to Haskell <beginners(a)haskell.org> > Subject: Re: [Haskell-beginners] Utrecht Summer School on Advanced > Functional Programming > Message-ID: > <CAKO4ktShf1trcLFwkjB8mnqGhw5AtRj1+YjUnjnnQ6-bhQdV2w(a)mail.gmail.com> > Content-Type: text/plain; charset="utf-8" > > Hi, > I am from India and I am a Haskell beginner level programmer. I am > interested in the summer school, but I won’t be able to attend in person. > Is there a provision for attending the lectures online? Also, is any > discount or fee waiver possible in my case as I cannot afford the full > amount? > > Vinod. > > On Thu, 20 Mar 2025 at 9:29 PM, Wouter Swierstra <w.s.swierstra(a)uu.nl> > wrote: > >> >> # Call for Participation >> >> SUMMER SCHOOL ON ADVANCED FUNCTIONAL PROGRAMMING >> >> Utrecht, the Netherlands, 07 July – 11 July 2025 >> >> https://urldefense.proofpoint.com/v2/url?u=http-3A__www.afp.school_&d=DwIGa… >> >> **Please register before June 15th ** >> >> ## ABOUT >> >> The Advanced Functional Programming summer school has been running for >> more than fifteen years. We aim to educate aspiring Haskell programmers >> beyond the basic material covered by many textbooks. >> >> The lectures will cover several more advanced topics regarding the >> theory and practice of Haskell programming, including topics such as: >> >> * lambda calculus; >> * lazy evaluation; >> * generalized algebraic data types; >> * type families and type-level programming; >> * concurrency and parallelism. >> >> The summer school will be held in Utrecht and consists of a mix of >> lectures, labs, and a busy social program. >> >> ## PREREQUISITES >> >> We expect students to have a basic familiarity with Haskell >> already. You should be able to write recursive functions over >> algebraic data types, such as lists and trees. There is a great deal >> of material readily available that covers this material. If you've >> already started learning Haskell and are looking to take your >> functional programming skills to the next level, this is the course >> for you. >> >> ## DATES >> >> Registration deadline: June 15th, 2025 >> School: 07 July – 11 July 2025 >> >> ## COSTS >> >> € 950 euro - Profession registration fee >> € 500 euro - Student registration fee >> € 200 euro - Housing fee >> >> We will charge a registration fee of €950 (or €500 for students) to >> cover our expenses. This fee includes all lunches, dinners, and coffee >> breaks - you won't need to budget much else besides your travel. >> >> If this is problematic for you for any reason at all, please email the >> organisers and we can try to offer you a discounted rate or a fee >> waiver. We have a limited number of scholarships or discounts available >> for students that would not be able to attend otherwise, especially for >> women and under-represented minorities. >> >> ## FURTHER INFORMATION >> >> Further information, including instructions on how to register, is >> available on our website: >> >> https://urldefense.proofpoint.com/v2/url?u=http-3A__afp.school_&d=DwIGaQ&c=… >> _______________________________________________ >> Beginners mailing list >> Beginners(a)haskell.org >> https://urldefense.proofpoint.com/v2/url?u=http-3A__mail.haskell.org_cgi-2D… >> >

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Utrecht Summer School on Advanced Functional Programming
by Wouter Swierstra 21 Mar '25

21 Mar '25

# Call for Participation SUMMER SCHOOL ON ADVANCED FUNCTIONAL PROGRAMMING Utrecht, the Netherlands, 07 July – 11 July 2025 http://www.afp.school/ **Please register before June 15th ** ## ABOUT The Advanced Functional Programming summer school has been running for more than fifteen years. We aim to educate aspiring Haskell programmers beyond the basic material covered by many textbooks. The lectures will cover several more advanced topics regarding the theory and practice of Haskell programming, including topics such as: * lambda calculus; * lazy evaluation; * generalized algebraic data types; * type families and type-level programming; * concurrency and parallelism. The summer school will be held in Utrecht and consists of a mix of lectures, labs, and a busy social program. ## PREREQUISITES We expect students to have a basic familiarity with Haskell already. You should be able to write recursive functions over algebraic data types, such as lists and trees. There is a great deal of material readily available that covers this material. If you've already started learning Haskell and are looking to take your functional programming skills to the next level, this is the course for you. ## DATES Registration deadline: June 15th, 2025 School: 07 July – 11 July 2025 ## COSTS € 950 euro - Profession registration fee € 500 euro - Student registration fee € 200 euro - Housing fee We will charge a registration fee of €950 (or €500 for students) to cover our expenses. This fee includes all lunches, dinners, and coffee breaks - you won't need to budget much else besides your travel. If this is problematic for you for any reason at all, please email the organisers and we can try to offer you a discounted rate or a fee waiver. We have a limited number of scholarships or discounts available for students that would not be able to attend otherwise, especially for women and under-represented minorities. ## FURTHER INFORMATION Further information, including instructions on how to register, is available on our website: http://afp.school/

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Compiling project errors within a docker container
by Hercules Merscher 15 Jul '24

15 Jul '24

Hello folks, I've been developing a small side project (a small web app). I'm developing on a Macbook M1 Pro, however, I need to compile it to test against a linux/amd64 environment. I'm trying to use docker for that. I know it is emulated via VM in this case and performance will suffer, but it's not a big deal for me since it's just a toy project. I'm using stack as build tool and GHC 9.6. The `stack build --fast` command errors, hinting that it could be out of memory. ``` root@c5f07dbd83dc:/opt/app# stack build --fast -j 4 --allow-different-user ... Error: [S-7282] Stack failed to execute the build plan. While executing the build plan, Stack encountered the error: [S-7011] While building package rinha-0.1.0.0 (scroll up to its section to see the error) using: /root/.stack/setup-exe-cache/x86_64-linux/Cabal-simple_6HauvNHV_3.10.3.0_ghc-9.6.5 --verbose=1 --builddir=.stack-work/dist/x86_64-linux/ghc-9.6.5 build lib:rinha exe:rinha-exe --ghc-options " -fdiagnostics-color=always" Process exited with code: ExitFailure (-9) (THIS MAY INDICATE OUT OF MEMORY) ``` Initially, I thought it really could be out of memory as I'm using colima and had default configuration. Then I started colima giving it 4 CPUs and 16GiB memory: ``` $ colima start --cpu 4 --memory 16 -a x86_64 -t vz --vz-rosetta ``` The project starts building, stays like that for almost 1h, and then this error happens. I wouldn't like to spin up a server just to build a project that I will be running on my laptop, but I see myself without alternatives and I'm finding it weird since I never had such a problem with other languages and it's the first time I see it while doing some Haskell. Any tips? Best, Hercules

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FFI. unIO safety considerations
by Folsk Pratima 13 Apr '24

13 Apr '24

Also see [Haskell-beginners] FFI to POSIX libc; strerror (errnum); unfreed memory Exactly how unsafe this code is? What do I do about it? It is so very stupid to have a pure function strerror_r in the IO monad! StrError.hs import Control.Exception import Control.Monad.ST import Control.Monad.ST.Unsafe import Data.Word import Foreign.C.String import Foreign.C.String import Foreign.C.Types import Foreign.Marshal import Foreign.Ptr import Foreign.Storable foreign import ccall unsafe "strerror_r_portalbe.c strerror_r_portable" c_strerror_r :: CInt -> Ptr CChar -> CSize -> IO CInt memSet :: Ptr a -> Word8 -> Word32 -> IO (Ptr a) memSet ptr _ 0 = return ptr memSet ptr byte size = do let voidptr = castPtr ptr :: Ptr Word8 acts = map (\i -> pokeByteOff voidptr i byte) [0 .. fromIntegral (size - 1)] mapM_ id acts return ptr strError :: Int -> String strError errnum = runST $ unsafeIOToST ioString where buflen = 512 :: CSize ioString = allocaBytes (fromIntegral buflen) $ \ptr -> do zeroptr <- memSet ptr 0 (fromIntegral buflen) code <- c_strerror_r (fromIntegral errnum) ptr buflen -- heuristic! case code of 22 -> return $ "Unknown error " ++ show errnum -- this is very dangerous, as far as I understand, and nobody in -- his right might should not do it if he later intends to -- unsafely escape IO 34 -> throwIO $ userError $ "strError: " ++ show code ++ ": ERANGE: " ++ "Numerical result out of range: " ++ "this is internal an error, which means not enough space " ++ "was allocated to store the error. You can not recover" _ -> peekCAString ptr main = mapM_ (putStrLn) $ map strError [1 .. 1000] strerror_portable.c #define _POSIX_C_SOURCE 200112L #include <string.h> int strerror_r_portable (int e, char *c, size_t s) { return strerror_r (e, c, s); } The C code is needed because GHC uses _GNU_SOURCE, which I personally do not want to use. Besides, I do not know how to predict whether GHC will define _GNU_SOURCE or not, so this also feels more reliable. To compile, do $ mkdir lib $ gcc -c -o lib/portable.o strerror_portable.c $ ar -csr lib/portable.a lib/portable.o $ ghc StrError.hs lib/portable.a No leaks, of course.

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FFI to POSIX libc; strerror (errnum); unfreed memory
by Folsk Pratima 12 Apr '24

12 Apr '24

I need to turn POSIX errno to the error string. StrError.hs import Foreign.C.String import Foreign.C.Types foreign import ccall unsafe "strerror" c_strerror :: CInt -> IO CString strError :: Int -> IO String strError i = do cstr <- c_strerror ci peekCAString cstr where ci = fromIntegral i main = mapM_ (>>= putStrLn) $ map strError [1 .. 450] $ ghc -g StrError.hs $ valgrind --leak-check=full --show-leak-kinds=all ./StrError ==2350== ==2350== HEAP SUMMARY: ==2350== in use at exit: 18 bytes in 1 blocks ==2350== total heap usage: 685 allocs, 684 frees, 97,998 bytes allocated ==2350== ==2350== 18 bytes in 1 blocks are still reachable in loss record 1 of 1 ==2350== at 0x48407B4: malloc (vg_replace_malloc.c:381) ==2350== by 0x496A427: __vasprintf_internal (vasprintf.c:71) ==2350== by 0x493DBD5: asprintf (asprintf.c:31) ==2350== by 0x498A9F0: strerror_l (strerror_l.c:45) ==2350== by 0x408BC0: ??? (StrError.hs:8) ==2350== ==2350== LEAK SUMMARY: ==2350== definitely lost: 0 bytes in 0 blocks ==2350== indirectly lost: 0 bytes in 0 blocks ==2350== possibly lost: 0 bytes in 0 blocks ==2350== still reachable: 18 bytes in 1 blocks ==2350== suppressed: 0 bytes in 0 blocks ==2350== ==2350== For lists of detected and suppressed errors, rerun with: -s ==2350== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0) I am already frustrated with having to use IO for this. I feel like it is better to manually create a pure solution by copying whatever the C code from libc does. But I still do not understand what causes this memory to remain reachable. Calling strerror from pure C code does not leave reachable memory regions. Can anyone explain? And maybe you have a suggestion as to how to implement this strError function properly? Just in case you are the type of a person to inquire as to *why* I need this, for fun. I need it for fun.

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