- Haskell-Cafe - Haskell.org

can a lazy language give fast code?
by Scott J. 31 Jul '02

31 Jul '02

Hi, Can one write withthe Haskell compliler faster code than in the examples of http://www.bagley.org/~doug/shootout/ where GHC (old Haskell 98?) seems to be much slower than Ocaml or Mlton both strict functional languages. Can one expect any improvements in speed in the future? Cheers Scott

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Re: Infix expressions
by Yoann Padioleau 30 Jul '02

30 Jul '02

Ken Shan <ken(a)digitas.harvard.edu> writes: > --a8Wt8u1KmwUX3Y2C > Content-Type: text/plain; charset=us-ascii > Content-Disposition: inline > Content-Transfer-Encoding: quoted-printable > > Hello, > > In Haskell, backquotes can be used to convert individual identifiers > into infix operators, but not complex expressions. For example, > > [1,2,3] `zip` [4,5,6] > > is OK, but not > > [1,2,3] `zipWith (+)` [4,5,6] > > Is there any reason other than potential confusion when one of the two > backquotes is accidentally omitted? > > In any case, perhaps some people on this mailing list would appreciate > the following implementation of "infix expressions" that Dylan Thurston > and I came up with -- as algebraic and perverse as we could manage: > > infixr 0 -:, :- > data Infix f y =3D f :- y > x -:f:- y =3D x `f` y > > main =3D print $ [1,2,3] -: zipWith (+) :- [4,5,6] This is a funny tricks. Does some people know other kind of tricks (possibly in other functionnal langage) ? > > --=20 > Edit this signature at http://www.digitas.harvard.edu/cgi-bin/ken/sig > The trick is that there is no trick. > > --a8Wt8u1KmwUX3Y2C > Content-Type: application/pgp-signature > Content-Disposition: inline > > -----BEGIN PGP SIGNATURE----- > Version: GnuPG v1.0.7 (GNU/Linux) > > iD8DBQE9RZgzzjAc4f+uuBURAjl6AKCQmYb0HJvk2VicBlRD6zRX9VfRRgCg9F2B > YPXu07Uqrz8pj2iUt+HVM3U= > =WjJq > -----END PGP SIGNATURE----- > > --a8Wt8u1KmwUX3Y2C-- > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > -- Yoann Padioleau, INSA de Rennes, France, Opinions expressed here are only mine. Je n'écris qu'à titre personnel. **____ Get Free. Be Smart. Simply use Linux and Free Software. ____**

1 0

Infix expressions
by Ken Shan 29 Jul '02

29 Jul '02

Hello, In Haskell, backquotes can be used to convert individual identifiers into infix operators, but not complex expressions. For example, [1,2,3] `zip` [4,5,6] is OK, but not [1,2,3] `zipWith (+)` [4,5,6] Is there any reason other than potential confusion when one of the two backquotes is accidentally omitted? In any case, perhaps some people on this mailing list would appreciate the following implementation of "infix expressions" that Dylan Thurston and I came up with -- as algebraic and perverse as we could manage: infixr 0 -:, :- data Infix f y = f :- y x -:f:- y = x `f` y main = print $ [1,2,3] -: zipWith (+) :- [4,5,6] -- Edit this signature at http://www.digitas.harvard.edu/cgi-bin/ken/sig The trick is that there is no trick.

3 2

Haskell is more known than we might think
by oleg＠pobox.com 29 Jul '02

29 Jul '02

Hello! The other day I received, among other junk mail, coupons for the local 7-eleven store. I subconsciously scanned the envelope, and almost jumped when I read the return address: 7-Eleven, Inc. 2711 North Haskell Avenue Dallas, TX 75204 It seems a rather long Avenue (with at least 27 blocks); presumably it has the Southern part too. Being associated with the most successful worldwide convenience store chain bodes well for the language.

1 0

(no subject)
by Scott J. 28 Jul '02

28 Jul '02

I think I am in the wrong pub. It seems I am alone here. Scott

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Uluslararas� �� FIRSATI..
by �� F�rsat� 28 Jul '02

28 Jul '02

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1 0

converting capital letters into small letters
by Karen Y 27 Jul '02

27 Jul '02

6 5

Doubts...
by Pedro L. P. Dias 27 Jul '02

27 Jul '02

Dear Professor: My name is Carlos Alexandre Grimaldi. I'm engineering student at Federal University of Rio de Janeiro, Brazil. I began my studies in Haskell, and I have some doubts which I report here. I'm very gratefully if you could help me. I'm following a book I downloaded from Internet: "A Gentle Introduction to Haskell, Version 98". Following this, I face some problems: - "inc :: Integer -> Integer" don't work - "inc n = n+1" don't work too; - "data Bool = False | True" also...; - "data Color = Red | Green | Blue | Indigo | Violet" also fails. I thought that this commands and definitions must be inside a program, and don't at prompt "prelude>". So, I opened other book, also downloaded from Internet: "The Hugs 98 User Manual", and I tryed: "module Fact where fact :: Integer -> Integer fact n = product [1..n]" thinking that would be created a file "Fact", in which the definitions for "fact" would work. But this also yield an error... So, I ask you: - is necessary the creation of a file where that definitions could work? - is this file a ".hs"? - how can I create a file like this? Which command or editor? - or, if I wrong, why that examples don't work? Thank you very much for your help. Best regards, Carlos A. Grimaldi.

2 1

RE: converting capital letters into small letters
by Garner, Robin 26 Jul '02

26 Jul '02

> 1. How would I convert capital letters into small letters? > > 2. How would I remove vowels from a string? I expect the first problem is actually to convert the upper case letters in a string to lower case, as the single-character version isn't a very interesting problem. A little thought shows that the first problem can be expressed as both a catamorphism or an anamorphism. The anamorphic solution would be [(p,f)] where p as = as == [] and f (a:as) = (makeLowerCase a, bs). The solution to the second problem is clearly a catamorphism, and one solution might be (|[],g|) where g (a:as) = if isVowel a then as else a:as The definitions of 'makeLowerCase' and 'isVowel' are quite simple (assuming English/Ascii, as pointed out in other messages), while finding the prelude functions for the patterns of recursion might take a little more thought. Suitable, possible, as homework questions in an introductory Haskell course ... Robin

1 0

Re: converting capital letters into small letters
by Ashley Yakeley 26 Jul '02

26 Jul '02

At 2002-07-25 19:07, Andrew J Bromage wrote: >> 1. How would I convert capital letters into small letters? >> 2. How would I remove vowels from a string? > >As you've probably found out, these are very hard problems. The build process of my HBase project automatically downloads the official data files from the Unicode web-site and automatically converts them into useful Haskell functions by the miracle of m4 -- including this one: toUpperCase :: Char -> Char; I also have the names for all the characters, because hard-drive space is cheap: getCharacterName :: Char -> String; ...and many other useful normative and informative character properties, such as general category, etc. See <http://sourceforge.net/projects/hbase/>. Mind you it's in a bit of an odd state right now. As for vowels, I'm pretty sure Unicode has nothing to say on the subject, as different languages may share the same characters but have different ideas as to what is and what isn't a vowel. -- Ashley Yakeley, Seattle WA

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Uluslararas� �� FIRSATI..
by �� F�rsat� 25 Jul '02

25 Jul '02

Uluslararası amerikan firması sağlık, kozmetik, gıda ve telekomünikasyon alanında uluslar arası çalışma imkanı tanıyor. Önkoşulsuz, sermayesiz ve risksiz. Dilerseniz ek gelir dilerseniz milyon $ 'lık bir iş; .......ve bağımsız! İlgileniyorsanız. AYLA HAYBAT wayscanada(a)hotmail.com Ayrıntılı Bilgi: www.herbalife.com ---------------------------------------------------------------------------------------------------------------------------- AMERİKA GREEN CARD GÖÇMENLİK ÇEKİLİŞİ KANADA GÖÇMENLİĞİ İNGİLTERE DE ÜCRETSİZ ingilizce EĞİTİM..... BİLGİ İÇİN www.myvizyon.com u ziyaret ediniz....

1 0

Size �zell....
by seni＠istiyorum.com 24 Jul '02

24 Jul '02

Sizler icin cok ozel býr sýte hazýrladýk http://www.pembelisex.com Bu adreste 18 kategoride 100 lerce galeri binlerce resim ve video ya ulaþabilirsiniz. http://www.pembelisex.com --------------------------------------------------------------------

1 0

Re: large binaries
by Jon Cast 24 Jul '02

24 Jul '02

Malcolm Wallace <Malcolm.Wallace(a)cs.york.ac.uk> wrote: > > > > Is there some reason haskell binaries have to be statically > > > > linked? > It would not be entirely fair to lay all the blame for large Haskell > binaries entirely at the door of static vs. dynamic linking. Well, considering that compiling the C binary statically linked produces an even bigger executable: $ gcc -static hello.c -o hello_c $ ls -l hello_c hello_hs -rwxrwxr-x 1 jcast jcast 441624 Jul 23 20:56 hello_c -rwxrwxr-x 1 jcast jcast 157028 Jul 18 14:08 hello_hs I think dynamic linking is fair game :) > After all, the Haskell version is dynamically linked against exactly > the same shared libraries as the C version, at least on my machine: > ldd Hello (Hello.hs) > libm.so.6 => /lib/libm.so.6 (0x40022000) > libc.so.6 => /lib/libc.so.6 (0x40044000) > /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x40000000) > Of course, it is static linking against the *Haskell* runtime > system, Prelude and Libraries that is the cause of binary bloat. > Quite simply, lots of extra stuff is dragged in that isn't visible > in the apparently simple source program. For instance, I can find > all the following symbols in the binary for "hello world" (compiled > with nhc98): > putStr, shows, showChar, showParen, showString, fromCString, > toCString, hGetFileName, hPutChar, hPutStr, error, flip, id, init, > length, not, putChar, putStrLn, seq, show, subtract, exitWith, > instance Bounded Int (maxBound, minBound), instance Enum Ordering > (succ, pred, toEnum, fromEnum, enumFrom, enumFromThen, enumFromTo, > enumFromThenTo), instance Enum ErrNo (succ, pred, toEnum, > fromEnum, enumFrom, enumFromThen, enumFromTo, enumFromThenTo), > instance Monad IO (>>=, >>, return, fail), instance Eq ErrNo (==, > /=), instance Eq Int (==, /=), instance Eq Ordering (==, /=), > instance Num Int (+, -, *, negate, abs, signum, fromInteger), > instance Ord Int (compare, <, <=, >=, >, max, min), instance Show > ErrNo (show, showsPrec, showList), instance Show IOError (show, > showsPrec, showList), instance Show Int (show, showsPrec, showList) Well, look at the symbols I find in the statically linked C hello world: _Exit _GLOBAL_OFFSET_TABLE_ _IO_2_1_stderr_ _IO_2_1_stdin_ _IO_2_1_stdout_ _IO_adjust_column _IO_adjust_wcolumn _IO_cleanup _IO_default_doallocate _IO_default_finish _IO_default_imbue _IO_default_pbackfail _IO_default_read _IO_default_seek _IO_default_seekoff _IO_default_seekpos _IO_default_setbuf _IO_default_showmanyc _IO_default_stat _IO_default_sync _IO_default_uflow _IO_default_underflow _IO_default_write _IO_default_xsgetn _IO_default_xsputn _IO_do_write _IO_doallocbuf _IO_fclose _IO_file_attach _IO_file_close _IO_file_close_it _IO_file_doallocate _IO_file_finish _IO_file_fopen _IO_file_init _IO_file_jumps _IO_file_open _IO_file_overflow _IO_file_read _IO_file_seek _IO_file_seekoff _IO_file_setbuf _IO_file_stat _IO_file_sync _IO_file_underflow _IO_file_write _IO_file_xsgetn _IO_file_xsputn _IO_flockfile _IO_flush_all _IO_flush_all_linebuffered _IO_flush_all_lockp _IO_fopen _IO_fprintf _IO_free_backup_area _IO_free_wbackup_area 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_nl_value_types _pthread_cleanup_pop_restore _pthread_cleanup_push_defer _quicksort _r_debug _setjmp _start _sys_errlist _sys_nerr _tens_in_limb _tens_in_limb _tens_in_limb _tmbuf abort access add_dependency add_derivation add_module add_name_to_object add_to_global addmntent alias_compare aliasfile.1 alt_digits alt_digits_initialized arena_get2 arena_key arena_mem argz_add_sep argz_count argz_create_sep argz_stringify blanks blanks brk bsearch buf.2 buffered_vfprintf builtin_aliases builtin_modules cache cache_malloced cache_new cache_size cachesize call_gmon_start calloc capstr category_to_name cfree check_action chunk_align chunk_alloc chunk_free chunk_realloc clearenv close codeset_idx.0 collseqmb collseqwc completed.1 compute_change compute_tzname_max curwd.0 data data_start daylight dcgettext decompose_rpath default_gconv_path default_tzdir.0 derivation_compare detect_conflict disallow_malloc_check dl_open_worker do_always_noconv do_dlclose do_dlopen do_dlsym do_encoding do_in do_length do_max_length do_out do_release_all do_release_shlib do_unshift dummy_bucket.3 empty_path_elem endmntent env_path_list environ envlock era_initialized eras errno exit expand_dynamic_string_token expected.1 expected_note.2 extend_alias_table fclose fcloseall fcntl fgets_unlocked find_derivation find_module find_module_idx fini_dummy fixup flockfile flush_cleanup fopen force_to_data force_to_data fprintf frame_dummy fread_unlocked free free_atfork free_check free_derivation free_mem free_mem free_mem free_mem free_mem free_mem free_mem free_mem free_mem free_mem free_mem free_mem free_mem free_mem free_mem free_modules_db free_starter freemem.1 freemem_size.2 freeres fromidx fromlimit froms fseek ftrylockfile funlockfile gcc2_compiled. gcc2_compiled. gcc2_compiled. gcc2_compiled. gcc2_compiled. gconv_conf_filename gconv_module_ext gen_steps get_avphys_pages get_nprocs get_nprocs_conf get_phys_pages get_proc_path getcwd getdelim getdtablesize getegid getenv geteuid getgid getmntent_r getpagesize getpid getrlimit getuid group_number group_number gsignal guess_category_value hack_digit.0 hashfraction hasmntopt heap_trim increment_counter index init init_dummy init_dummy initial internal internal_trans_names.0 ioctl is_initialized.0 isatty isinf isinfl isnan isnanl jump_table.0 kcount kcountsize kill known_compare known_derivations known_values last_environ leaps list_all_lock list_lock llseek loaded locale_alias_path.0 localtime localtime_offset localtime_r lock lock lock lock lock lock lock.0 lock.1 log_hashfraction longjmp lose lowpc lseek lseek64 main main_arena main_trim mallinfo malloc malloc_atfork malloc_check malloc_get_state malloc_hook_ini malloc_set_state malloc_starter malloc_stats malloc_trim malloc_usable_size mallopt map map match_symbol max_capstrlen max_dirnamelen max_mmapped_mem max_n_mmaps max_sbrked_mem maxmap mbrlen mbrtowc mbsnrtowcs mem2chunk_check memalign memalign_check memalign_hook_ini memchr memcpy memmove mempcpy memset mktime mmap mmap_threshold mmapped_mem modcounter.0 mount_proc mprotect mremap msg.9 msort_with_tmp munmap n_mmaps n_mmaps_max narcs narcsp nbits.0 nbits.0 nbits.0 ncapstr new_do_write new_heap nmap not_available nsamples null num_eras num_leaps num_transitions num_types oact.0 object.2 old_tz once open open64 open_path open_verify openaux otimer.1 p.0 pagesize.1 path_proc pc_offset pc_scale phys_pages.0 phys_pages_info plone plural_eval plural_lookup plvar posix_memalign print_search_path printf printf_funcs printf_unknown profil profil_counter profile_fixup program_invocation_name program_invocation_short_name ptmalloc_init ptmalloc_init_all ptmalloc_lock_all ptmalloc_unlock_all pvalloc qsort raise rawmemchr read read_alias_file read_conf_file readlink realloc realloc_check realloc_hook_ini receiver register_printf_function release_handle result.1 rindex root rtld_search_dirs rule_dstoff rule_stdoff run_fp running samples save_arena save_for_backup save_for_wbackup save_free_hook save_malloc_hook sbrk sbrk_base search_tree setenv setitimer setlocale setmntent sigaction sigfillset siglongjmp sigprocmask sscanf stage state state state state stderr stdin stdout step0_jumps.1 step1_jumps.2 step2_jumps.3 step3a_jumps.4 step3b_jumps.5 step4_jumps.6 step4_jumps.7 stpcpy strcasecmp strchr strchrnul strcmp strcpy strdup strerror_r string_space string_space_act string_space_max strncasecmp strncmp strndup strnlen strpbrk strrchr strsep strstr strtod strtof strtol strtold strtoll strtoq strtoul strtoull strtouq sys_errlist sys_nerr sysconf system_dirs system_dirs_len tcgetattr tdelete tdestroy tdestroy_recurse textsize tfind timelocal timezone to_mb to_wc top_check top_pad tos trans_compare transcmp transitions translit_from_idx translit_from_tbl translit_to_idx translit_to_tbl transmem_list trecurse trim_threshold tsearch twalk type_idxs types tz_rules tzname tzset tzset_internal tzset_lock tzstring_list uname undefined_msg unsecure_envvars.0 unsetenv using_malloc_checking valloc vfprintf vfscanf vsscanf walt_digits walt_digits_initialized wcrtomb wcschr wcslen wcsnlen wcsrtombs wmemcpy wmemmove wmempcpy write writev yycheck yydefact yydefgoto yypact yypgoto yyr1 yyr2 yytable yytranslate zeroes zeroes zone_names The point is, /both/ libraries have a lot of code re-use. Dynamic linking puts that code re-use in some random .so in $foo/lib; static linking puts it in your executable. That's the major difference. (The minor difference is that most Haskell implementations use libc more than most C implementations use the Haskell standard libraries.) > This is not the fault of any particular implementation - the > ghc-built binary has a similar collection - rather it is dictated by > the nature of the language and its standard libraries. Because > Prelude functions are small and re-usable, they do get used all over > the place in the implementation of other parts of the Prelude, so > you end up with a huge dependency graph hiding underneath the > simplest of calls. You mean like printf("Hello, world!\n")? > In fact, most of the extra stuff in "Hello World" is there purely to > handle all possible error conditions in the I/O monad. You mean as opposed to C, where most of the extra stuff is there purely to support number formatting? > Several years ago, Colin Runciman and I did the experiment of > removing all the nice error-handling stuff from the prelude (and > eliminating a few classes too I think), to see just how small we > could squash "Hello World". The idea was to target embedded systems > where memory is a scarce resource, and fancy error-reporting is > pointless (a single red LED would do). IIRC, we managed to achieve > a size of 25kb, compiled with nhc98, which don't forget includes a > bytecode interpreter in the runtime system. > Regards, > Malcolm To sum up: code re-use within a library certainly happens in more languages than just Haskell :) So don't blame code re-use for Haskell-specific (or non-specific) problems, because code re-use is not a Haskell-specific cause. Jon Cast

2 1

A question
by Nick Name 23 Jul '02

23 Jul '02

First, hi all. I am an haskeller newbie looking forward to conquer the world with a functional language. Part of this conquer involves IMHO writing a nice desktop, using modern features of opengl, to make it portable. But, a question arises: all opengl true type font renderers are written in C++, no one is written in C. If I want to write haskell bindings for such a thing, what can I do? Vincenzo Ciancia

3 3

Re: conditional
by Jon Cast 23 Jul '02

23 Jul '02

Jonata Goulart <jonatahh(a)hotmail.com> wrote: > How do I write a multiple tine conditional in Haskell. I guess you mean ``line''? :) > Example: This would work on language like C. > if (x==1) { > x = x +1; > x = x +2; > x = x +3; > } Well, this example has more problems in Haskell than the multi-line if statement. I don't think you can implement a C-like `=' in Haskell 98. In GHC you can give `x' type `IORef Int', and write the first line of the conditional like this: do xval <- readIORef x x `writeIORef` (xval + 1) Note that, in Haskell, this is two lines. <aside authority="Jon's tenuous understanding"> In general, the order in which side effects (including reading mutable variables) occur depends on the evaluation order, and the meaning of the program depends on the order of side effects. Haskell expressions in general contain have very little information about the evaluation order, and therefore (if they have embedded expressions with side effects) about the program's behavior. This is bad, since the program's behavior is not obvious from the source code. The solution Haskell adopts, as I understand it, is to supply the `do' construct to make the order of evaluation explicit. So, since the C statement `x = x + 1' contains two side effects, we need to use `do' to explicitly specify the order of those side effects. </aside> This should answer your main question (almost). You write the body of a multiple line conditional the same way you write any other multiple line program: do xval <- readIORef x if xval == 1 then do xval <- readIORef x x `writeIORef` (xval + 1) xval <- readIORef x x `writeIORef` (xval + 2) xval <- readIORef x x `writeIORef` (xval + 3) else return () Note that, in Haskell, the `if' construct forms and /expression/, not a statement. Therefore, you have to provide an `else' clause. > Thanks. Jon Cast

1 0

LRparsing combinators
by andy 23 Jul '02

23 Jul '02

Has anyone seen or have a reference to LR based parsing combinators? Andy Gill

2 1

conditional
by Jonata Goulart 22 Jul '02

22 Jul '02

How do I write a multiple tine conditional in Haskell. Example: This would work on language like C. if (x==1) { x = x +1; x = x +2; x = x +3; } Thanks. _________________________________________________________________ Chat with friends online, try MSN Messenger: http://messenger.msn.com

1 0

RE: large binaries
by Simon Marlow 19 Jul '02

19 Jul '02

> > Is there some reason haskell binaries have to be statically linked? > > I can't seem to find a way to make them otherwise, at least with > > ghc. > > The ELF dynamic linking format seems to be designed on the assumption > of poor code reuse (e.g., C code) where calls from one module to > another are rare and can therefore be expensive. > > Haskell code has very high levels of reuse and calls from one module > to another (especially calls into Prelude, List, Monad, etc) are very > common so dynamic linking imposes a very high overhead. > > This isn't a reason to not support dynamic linking but it's a reason > to make it a low priority. Incidentally, it avoids confusion between > the performance overhead of lazy evaluation and the performance > overhead of dynamic linking of modular code. Yes, and there are various other reasons too. There's a FAQ question in GHC's (rather well hidden) FAQ: http://www.haskell.org/ghc/docs/latest/html/users_guide/faq.html and a search through the glasgow-haskell-users archives will turn up previous discussions. Also, we do (or did) have support for dynamic libraries on Windows. Cheers, Simon

3 2

Re: large binaries
by Jon Cast 18 Jul '02

18 Jul '02

Abraham Egnor <aegnor(a)antioch-college.edu> wrote: > This is something I just noticed... > hello.hs: > module Main(main) where > main = putStr "Hello world!\n" > hello.c: > #include <stdio.h> > int main(void) > { > printf("Hello world!\n"); > return 0; > } > [abe@shiva:~/src/test] $ ghc hello.hs -o hello_hs > [abe@shiva:~/src/test] $ gcc hello.c -o hello_c > [abe@shiva:~/src/test] $ ls -l hello_* > -rwxr-xr-x 1 abe engy 13712 Jul 18 11:34 hello_c > -rwxr-xr-x 1 abe engy 299900 Jul 18 11:33 hello_hs > > Why is the binary made by ghc 20 times bigger than the one made by gcc? I don't know for certain, but I've got a couple of guesses: 1. hello_hs is probably statically linked. hello_c is probably dynamically linked. 2. "Hello world!\n" in Haskell is boxed; in C it's un-boxed. Ditto for putStr vs. printf. The compiled code for the Haskell main appears to have a lot of code to deal with those complications; multiply that by however many functions are called by putStr. > Abe Jon Cast

4 3

large binaries
by Abraham Egnor 18 Jul '02

18 Jul '02

This is something I just noticed... hello.hs: module Main(main) where main = putStr "Hello world!\n" hello.c: #include <stdio.h> int main(void) { printf("Hello world!\n"); return 0; } [abe@shiva:~/src/test] $ ghc hello.hs -o hello_hs [abe@shiva:~/src/test] $ gcc hello.c -o hello_c [abe@shiva:~/src/test] $ ls -l hello_* -rwxr-xr-x 1 abe engy 13712 Jul 18 11:34 hello_c -rwxr-xr-x 1 abe engy 299900 Jul 18 11:33 hello_hs Why is the binary made by ghc 20 times bigger than the one made by gcc? Abe

1 0

会议提醒
by ee31＠163.com 16 Jul '02

16 Jul '02

1 0

RE: replacing the Prelude (again)
by Simon Peyton-Jones 15 Jul '02

15 Jul '02

I'm fond of the idea proposed by Marcin 'Qrczak' Kowalczyk: | May I propose an alternative way of specifying an alternative Prelude? | Instead of having a command line switch, let's say that 3 always means | Prelude.fromInteger 3 - for any *module Prelude* which is in scope! That's a perfectly reasonable idea, but GHC can't make it the default because it's not H98. It *would* be possible to make GHC's -fno-implicit-prelude flag mean that 3 means Prelude.fromInteger 3 rather than fromInteger 3 I quite like the fact that you would then have to say import MyPrelude as Prelude thereby stressing that you are importing the Prelude stuff. But it would be that *plus* -fno-implicit-prelude, I'm afraid. If there were a consensus in favour of this I'll gladly do it (5 min job). | anymore. What I would like is that the defualting rules refer | to the classes in my version of the Prelude, | not the Standard Prelude. You can always get that (with the -fno-implicit-prelude thing) by adding default [Int, Double] or whatever to your source module, just after the import that gets your new standard Prelude. Doesn't that do it? It would also not be hard to arrange that the "default default" declaration became scoped with -fno-implicit-prelude (like fromInteger), if that was useful. It's a good point; I thought that *all* the numeric stuff was un-coupled from the Prelude with -fno-implicit-prelude, but it isn't quite. Simon

1 0

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by houshen2 15 Jul '02

15 Jul '02

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1 0

replacing the Prelude (again)
by Bernard James POPE 14 Jul '02

14 Jul '02

Hi all, Sorry to dig up an old topic, but I think this is an important one. (at least it is for me). I have run into a problem recently. I am writing a debugger for Haskell. It is based on a source-to-source transformation. The important bit is that the type of functions changes under the transformation. If you want to debug calls into the Standard Prelude (yes this is useful) then a transformed Prelude must be used. The idea being that a transformed program imports a transformed Prelude. That's okay, my debugger can transform all of the Standard Prelude since it is just a Haskell module (with provisions for primitive functions of course). The problem is that when I replace the Standard Prelude with a transformed Prelude the defaulting mechanism doesn't work anymore. What I would like is that the defualting rules refer to the classes in my version of the Prelude, not the Standard Prelude. I am using ghc version 5.03, and I don't think -fno-implicit-prelude can help here. I do think that this issue is independent of the Haskell environment, and more an issue of the design of the language. Now there have already been some discussions about replacing the Standard Prelude with a non-Standard Prelude. The trick being that a fair degree of the language definition makes use of things in the Standard Prelude. See for example: Dylan Thurston Replacing the Prelude http://www.haskell.org/pipermail/haskell-cafe/2002-May/003032.html Primitive types and Prelude shenanigans http://www.haskell.org/pipermail/haskell-cafe/2001-February/thread.html#1641 I'm fond of the idea proposed by Marcin 'Qrczak' Kowalczyk: May I propose an alternative way of specifying an alternative Prelude? Instead of having a command line switch, let's say that 3 always means Prelude.fromInteger 3 - for any *module Prelude* which is in scope! That is, one could say: import Prelude () import MyPrelude as Prelude IMHO it's very intuitive, contrary to -fno-implicit-prelude flag. Presuming of course that defaulting would follow this path and refer to the new Prelude. I'm wondering if any further progress has been made towards this? Or perhaps someone can think of a temporary solution to my problem? Cheers, Bernie.

2 1

what's the difference?
by Cagdas Ozgenc 12 Jul '02

12 Jul '02

Greetings. What is the difference between the following two scenarios: 1) class Eq a where (==) :: a -> a -> Bool class Eq a => Ord a where ( < ) :: a -> a -> Bool 2) class Eq a where (==) :: a -> a -> Bool class Ord a where (eq),( < ) :: a -> a -> Bool instance Ord a => Eq a where (==) = eq eq is just a rename for == to avoid the nameclash The second scenario resembles Russell's Paradox. Typeclass of a typeclass. Anyhow we are loosing orthogonality here. Thanks

2 1

Job Advertisment
by Chris Dornan 11 Jul '02

11 Jul '02

The ARM Web site is advertising a Principal Research Engineer position; see http://www.arm.com/hr.nsf/iwpList61/90A8BD2585A0CE2F80256BF10051000F?OpenDo… and the summary attached to the end of this mail message. Note that although the job is for a Principal Research Engineer with a strong emphasis on microprocessor architecture, a high degree of proficiency in programming, preferably Haskell and C, is regarded as essential. Chris Dornan Principal Research Engineer ARM R&D cdornan(a)arm.com +44 (0)1223 400498 Principal Research Engineer, Cambridge Reference: 02MKRD003 The Research and Development Division are seeking a highly motivated individual who has research experience and who's interests lie in the fields of computer languages, microprocessor architecture, and/or microprocessor simulation. The successful candidate will be involved in a team developing next generation microprocessor architectures. As well as architecture development, this role will involve developing, implementing, and integrating a range of sophisticated tools to assist in the analysis of microprocessor architectures and implementations. The successful candidate will be working in an environment which allows experimentation and provides autonomy, but expects innovation and results; hence the candidate will be of a very high caliber. This post would suit a PhD graduate or someone with a background working in research in Industry. Skills Essential * A high degree of proficiency in programming (preferably in Haskell & C). * A good understanding of microprocessor architectures. * A working understanding of computer languages. * A background in Research and innovation.

1 0

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by web 11 Jul '02

11 Jul '02

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2 1

haskell.sty
by François Bédard 11 Jul '02

11 Jul '02

Hello, I find it interesting that Haskell should make native provision for a basic form of literate programming, and this immediately suggests, of course, the possibility of mixing code with LaTeX commands. The problem is that putting one's hand on a dedicated LaTeX extension doesn't seem so straightforward. The link to Andrew Cooke's haskell.sty is broken and I couldn't find the file at his new home (www.acooke.org/andrew/) Other possibilities such as Manuel Chakravarty's, lambdaTex and lhs2tex (which I, admittedly, have only looked at briefly) deviate from the \begin{code}...\end{code} suggested by the report and seem to require more (La)TeX proficiency on the part of the user. As my interest is to introduce the ideas of literate programming and LaTeX to people thorougly unfamiliar with such, I need to keep things as simple as possible - of special interest is the fact that a given file can be submitted as is to both hugs and latex, without the need for preprocessing. I've tried to address the question by redefining an existing environment \usepackage{moreverb} \newenvironment{code}{\begin{verbatimtab}[4]}{\end{verbatimtab}} but moreverb and the like depend on verbatim which is apparently the one environment you can't use like this and I'm no such LaTeX guru that I can come up with better alternatives. So the question is : would anyone know where to find haskell.sty (presuming that's what I need) or is there some fairly simple solution I've missed ? Thanks, François

3 4

Parsec question
by Eray Ozkural 10 Jul '02

10 Jul '02

Hi there, I'm hacking together a small parser for a subset of C++. I'm in trouble with left recursion as you may guess. What is the best way to write a parser for the part of grammar below in Parsec? Declarator -> Name -> PtrOper Declarator -> Declarator '(' ArgDeclarationList ')' [CvQualifierList] -> Declarator '[' [ConstantExp] ']' -> '(' Declarator ')' Here [X] denotes an optional non-terminal X, and all symbols starting with a capital letter are non-terminals. The remedies I thought of were using chainl or eliminating left recursion in the grammar. What do you think should be done in such a case? Regards, -- Eray Ozkural <erayo(a)bilkent.edu.tr> Comp. Sci. Dept., Bilkent University, Ankara www: http://www.cs.bilkent.edu.tr/~erayo GPG public key fingerprint: 360C 852F 88B0 A745 F31B EA0F 7C07 AE16 874D 539C

1 0

Fw: 2 Positions
by Manuel M. T. Chakravarty 06 Jul '02

06 Jul '02

Not 100% Haskell-related, but I thought some people on this list might be interested in these two open positions at UNSW. Manuel

1 0

Is there any algorithms for solving equation systems
by Daniel Andersson 04 Jul '02

04 Jul '02

Hi I looking for algorithms for solving equation systems and wonder if there is anyone that has seen an algorithm, either a numerical or an analytical, for solving equation systems in haskell. thanks Daniel _____________________________________________________ Följ VM på nära håll på Yahoo!s officielle VM-sajt www.yahoo.se/vm2002 Håll dig ajour med nyheter och resultat, med vinnare och förlorare...

1 0

Re: Writing a counter function
by Jon Cast 02 Jul '02

02 Jul '02

Mark Carroll <mark(a)chaos.x-philes.com> wrote: > On Sat, 29 Jun 2002, Samuel E. Moelius III wrote: > (snip) > > Here's another not-exactly-what-you-wanted solution. :) > (snip) > Do any of the experimental extensions to Haskell allow a > what-he-wanted solution? I couldn't arrange one in H98 without > something having an infinitely-recursive type signature. That's because the problem requires an infinitely-recursive type. > I'm sure it would have been easy in Lisp, and he already gave a Perl > equivalent, That's because both Lisp and Perl are weakly typed. Haskell is strongly typed. Consider Lisp: (defun self-apply (f) "Apply F to itself." (f f)) No problem (and I'm sure you can pull the same trick off in Perl). Consider Haskell: self-apply f = f f The *typing algorithm* (the thing that didn't complain in Lisp) proceeds roughly as follows: f is applied to at least one argument, so f must have type a -> b. Therefore, f's argument (f) must have type a. So, we conclude: f :: a -> b f :: a But f can only have one type, so we set its types equal: a = a -> b This is clearly recursive, right? > so I'm wondering if it could be at all sane for Haskell to allow > such stuff Sure. All it has to do is: 1. Create its own newtype in response to such things as `self-apply' above. 2. Ensure that self-apply f = f f and self-apply' g = g g have the same type. I would *love* to hear ideas on how to do that, but it's difficult. > and if Haskell is somehow keeping us on the straight and narrow by > disallowing the exact counter that was originally requested. Well, it's a more general problem than the `exact counter'. And, yes, Haskell is erring on the side of safety here; there's a reason it's called a ``statically typed language''. > The beauty of his request was that it was so simple and seemed to > make sense; I went ahead and tried to fulfill it before realising I > couldn't do it either. Well, it makes sense, yes. But I think learning to manually `unify' these things (add a newtype) is not hard, and probably useful --- Haskell is not the only statically-typed language out there. Learn how to solve this problem, and you understand the problem, the solution, typing, and life in general :) > -- Mark Jon Cast

3 2

Writing a counter function
by Shlomi Fish 01 Jul '02

01 Jul '02

I'm trying to write a counter function that would return a tuple whose first element is the current value and whose second element is a new counter. The following line: counter n = (n,(counter (n+1))) Generates the following error on Hugs and a similar one with ghci: ERROR "counter.hs":6 - Type error in function binding *** Term : counter *** Type : a -> (a,b) *** Does not match : a -> b *** Because : unification would give infinite type Is there any way to do it? I tried using data, type and newtype and none of them worked. Regards, Shlomi Fish ---------------------------------------------------------------------- Shlomi Fish shlomif(a)vipe.technion.ac.il Home Page: http://t2.technion.ac.il/~shlomif/ Home E-mail: shlomif(a)iglu.org.il He who re-invents the wheel, understands much better how a wheel works.

11 20

Defining instances of superclasses
by Zdenek Dvorak 01 Jul '02

01 Jul '02

Hello. I've got the following problem: I have class Structure, that says that its members have some internal parts that can be read from/written to Strings: >data StrItem a=forall b c.(Show b,Parse c)=>StrItem String (a->b) (a->c->a) > >class Structure a where > strName::a->String > strEmpty::a > strItems::[StrItem a] Now I would like to use it to create instances of Show and Parse (and perhaps others (for input/output from various formats, ...)). The approaches I have tried: 1) >instance Structure a => Show a where > showsPrec _ w = > showsStruct (strName w) (map showsPair strItems) > where > showsPair (StrItem fName fGet _)=(fName,shows $ fGet w) This is nice, but it only works in ghc with allowed overlapping and undecidable instances. It may not seem too important, when I use existential types anyway, but existential types are supported by at least one more implementation (hugs) and they seem to me to be a well defined extension that has good chances to become part of standard Haskell later; handling of overlapping and undecidable instances in ghc seems quite too much ad-hoc and experimental for me. 2) >newtype Str a=Str a >instance Structure a => Show (Str a) where > showsPrec _ (Str w) = > showsStruct (strName w) (map showsPair strItems) > where > showsPair (StrItem fName fGet _)=(fName,shows $ fGet w) This seems to be a standard way how to do it. The problem is, that I don't get Show instance for a, but for isomorphic type Str a; this is a bit annoying when I want to use it; also I may no longer use deriving Show on types containing such structure. Is there some better way how to do this? Zdenek Dvorak _________________________________________________________________ Send and receive Hotmail on your mobile device: http://mobile.msn.com

1 0

Greencard-Canada-Aupair
by Greencard 29 Jun '02

29 Jun '02

1 0

Biz Kurduk Ordan Biliyoruz
by �leti... 23 Jun '02

23 Jun '02

1 0

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by ��ȷ� 22 Jun '02

22 Jun '02

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1 0

Question about GUM
by Changming Ma 21 Jun '02

21 Jun '02

Hi there, I'm getting confused of the run-time system behavior of GUM. When I ran a quicksort program in GUM with profiling flag, I got different "task" distributions in the PS file generated everytime, e.g., the peak of task number may be 19 at the first time and 48 at the second. While it's quite reasonable that the clock cycles vary dramatically, it's somewhat strange to me that the task distributions are so different. Any hints? I do appreaciate it. BTW, seems the program does not stop if the input list has more than 350 elements, althought it works fine otherwise. Will it get better if I use an SMP system? Thanks in advance. PS: I'm using GUM-4.06, PVM3, RH LINUX6.2 on a single processor system. Program and RTS flags quicksort +RTS -qP -sstderr grs2gr *quicksort.???.gr > quicksort.gr gr2ps -o quicksort.ps quicksort.gr --source code module Main(main) where import System(getArgs) import Parallel forceList :: [a] -> () forceList [] = () forceList (x:xs) = x `seq` forceList xs quicksortF::[Int]->[Int] quicksortF [] = [] quicksortF [x] = [x] quicksortF (x:xs) = (forceList losort) `par` (forceList hisort) `par` losort ++ (x:hisort) where losort = quicksortF [y|y <- xs, y < x] hisort = quicksortF [y|y <- xs, y >= x] args_to_IntList :: [String] -> [Int] args_to_IntList a = if length a < 1 then error "Parallel Quick Sort: no enough args \n" else map read a main = putStr ("get " ++ (show (quicksortF l))++"\n") l = [ 658986,123141,737929,681645,329651, ... 925104]

1 0

% 6,95
by finans400 19 Jun '02

19 Jun '02

1 0

Data Tracing in GPH
by Ma Changming 17 Jun '02

17 Jun '02

Hi there, Does anyone know how to trace the GPH program to see the data processed at specific processors? I'm using gum-4.06, PVM3, RedHat Linux6.2. When I execute the following QuickSort program, I want to make sure what happens with different CPUs, i.e., how the data are partitioned between processors? Is there any debugging tools to trace the data? Thanks in advance. Changming Ma PS: QuickSort module Main(main) where import System(getArgs) import Parallel forceList :: [a] -> () forceList [] = () forceList (x:xs) = x `seq` forceList xs quicksortF::[Int]->[Int] quicksortF [] = [] quicksortF [x] = [x] quicksortF (x:xs) = (forceList losort) `par` (forceList hisort) `par` losort ++ (x:hisort) where losort = quicksortF [y|y <- xs, y < x] hisort = quicksortF [y|y <- xs, y >= x] args_to_IntList :: [String] -> [Int] args_to_IntList a = if length a < 1 then error "Parallel Quick Sort: no enough args \n" else map read a main = getArgs >>= \ a -> let l = args_to_IntList a in putStr ("get " ++ (show (quicksortF l))++"\n") __________________________________________________ Do You Yahoo!? Yahoo! - Official partner of 2002 FIFA World Cup http://fifaworldcup.yahoo.com

2 1

reversing a list
by Matthias 15 Jun '02

15 Jun '02

Hi there, I thought i can reverse a list with reverse a list easily with the reverse function in order to achieve following: I wanted to check for a certain suffix (then reversed a prefix) and substitute that. So i did -- let dstfile = case tmpfile of -- ('a':'s':'p':'.':rest) -> rest ++ ".psx" -- anything -> anything ++ ".psx" Guess what: I did not work. dstfile was reversed (tmpfile ++ ".psx"). i guess this deals with lazy evalutation, but would be glad about some definit ideas. Matthias

1 2

Say�n haskell-cafe ,
by abdyesilkart.com 13 Jun '02

13 Jun '02

1 0

typeclass versioning
by Cagdas Ozgenc 12 Jun '02

12 Jun '02

Greetings. What happens if a type is made an instance of a typeclass in two different modules with different implementations? In static linking scenarios it will be caught by the compiler. I don't know whether we can do dynamic loading in Haskell, but it seems there will be inconsistencies in that case. Even in static linking when an object is serialized over the wire where a different implementation of a typeclass exists things will go wild. What's Haskell's approach to versioning? Thanks

2 1

Generating the n! permutations in Haskell
by Shlomi Fish 10 Jun '02

10 Jun '02

Included below is a Haskell Program I wrote to generate the n! permutations of a set of n elements. There are comments that explain it throughout the program. Both of the algorithms that appear in the cut the knot site use assignment, so are not very suitable for Haskell. Regards, Shlomi Fish -- (gradual_transfer set empty_set) -- -- Gradually pops elements out of set and [1..5] pushes them into -- empty_set, -- and makes a list of both stacks in their intermediate phases. -- -- E.g: -- gradual_transfer [1 .. 5] [] = -- [([1,2,3,4,5],[]),([2,3,4,5],[1]),([3,4,5],[2,1]), -- ([4,5],[3,2,1]),([5],[4,3,2,1])] gradual_transfer :: [a] -> [a] -> [([a],[a])] -- I stop when the list contains a single element, not when it contains -- no elements at all. The reason for this is that gen_perms like it -- better -- this way, as it has no use of a zero element (a:as). gradual_transfer (a:[]) ps = [((a:[]),ps)] gradual_transfer (a:as) ps = ((a:as),ps):(gradual_transfer as (a:ps)) -- (dump ps as) is equivalent to (reverse ps) ++ as, only it should -- be much faster. dump :: [a] -> [a] -> [a] dump [] as = as dump (p:ps) as = dump ps (p:as) gen_perms :: [a] -> [[a]] gen_perms [] = [[]] gen_perms set = [ (a:rest) | (a:as,ps) <- (gradual_transfer set []), rest <- gen_perms(dump ps as) ] print_perms [] = return () print_perms (a:as) = do print a print_perms as main = print_perms (gen_perms [1 .. 8]) ---------------------------------------------------------------------- Shlomi Fish shlomif(a)vipe.technion.ac.il Home Page: http://t2.technion.ac.il/~shlomif/ Home E-mail: shlomif(a)iglu.org.il He who re-invents the wheel, understands much better how a wheel works.

2 2

Re: HTTP.hs with slow execution
by Warrick Gray 09 Jun '02

09 Jun '02

[redirecting to haskell-cafe] Hi Jens, I think I have it. >I think I found an issue with the HTTP.hs library when >making a short-lived non-persistent connection to a server >from a slower machine (i486). I can also reproduce it by >running my program with strace or ltrace on a faster machine >(PIII). Last two meaningful recv call: >recvfrom(3, 0x500a3878, 1000, 0, 0x500a3c68) = 555 >getpeername(3, 0x500a3c8c, 0x500a3ca4, 0x080dfda0, 1) = 0 >recvfrom(3, 0x500a2008, 1000, 0, 0x500a23f8) = 0 >getpeername(3, 0x500a241c, 0x500a2434, 0x080dfda0, 1) = 0 After no data is received the sending part of the TCP stream is closed: >shutdown(3, 1, 0x0805b85f, 0x080e018c, 1) = 0 Being polite, the library ensures that all incoming data has been consumed, forgetting for a moment that the incoming stream has already closed: >recvfrom(3, 0x500a2440, 1000, 0, 0x500a2830) = 0 >getpeername(3, 0x500a2854, 0x500a286c, 0x080e018c, 1) = -1 The "recvfrom" seems fine, the "getpeername" call comes from the definition of Network.Socket.recvFrom, which features: flg <- sIsConnected sock -- For at least one implementation (WinSock 2), recvfrom() ignores -- filling in the sockaddr for connected TCP sockets. Cope with -- this by using getPeerName instead. sockaddr <- if flg then getPeerName sock else peekSockAddr ptr_addr ...Leading to the error in question: >strerror(107) = "Transport endpoint is >not connec"... The answer I guess is to alter all calls to 'recvFrom' to 'recv' calls (done), or replace socket reference with ConnClosed at the first sign of a closed socket. Unfortunately the second will have to wait, but the first is implemented and available in the latest version: http://homepages.paradise.net.nz/warrickg/haskell/http Warrick. PS - nice trace. _________________________________________________________________ Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp.

2 1

problems figuring out what the type system is telling me
by Chris Moline 08 Jun '02

08 Jun '02

hi. i am really stuck on this problem and i cant seem to figure it out and so i am posting this in the hopes someone will help me. i realize you prolly get this kind of question alot but the wiki and the papers i have been reading arent helping to clarify things. i am trying to write a little utility to make it easier to get rid of ports on my machine. the function that is giving me trouble is getDepends. it takes the name of a port and opens the appropriate +CONTENTS file and returns the dependencies it finds. here is the function and its helper. getDepends :: String -> [String] getDepends p = do handle <- openFile (portsDir ++ p) ReadMode fetchDepends handle fetchDepends :: Handle -> [String] fetchDepends handle = do l <- hGetLine handle e <- hIsEOF handle case (not e) of -- ifs keep giving indent errors so ill just use case True -> case (matchRegex (mkRegex "^@pkgdep") l) of Just [a] -> [drop 8 l] ++ (fetchDepends handle) _ -> fetchDepends handle False -> "" here is ghci's error messages. Compiling Pheobe ( Phoebe.hs, interpreted ) Phoebe.hs:19: Couldn't match `[]' against `IO' Expected type: [t] Inferred type: IO Handle In the application `openFile (portsDir ++ p) ReadMode' In a 'do' expression pattern binding: handle <- openFile (portsDir ++ p) ReadMode Phoebe.hs:24: Couldn't match `[]' against `IO' Expected type: [t] Inferred type: IO String In the application `hGetLine handle' In a 'do' expression pattern binding: l <- hGetLine handle Failed, modules loaded: none. could someone be so kind as to explain what the problem is? sincerly, chris moline

4 4

type equivalency
by Cagdas Ozgenc 06 Jun '02

06 Jun '02

Greetings. I know 2 special type constructors(there might be other that I do not know yet) -> and ( , ) where structural type equivalency is enforced and we can also create new types with an algebric type constructor notation where name equivalency is enforced. What is the rationale? I mean why 2 special type constructors, but not 5, or 10 or N? Thanks for taking time.

5 8

(no subject)
by xoo 06 Jun '02

06 Jun '02

hi.. i was just wondering if some body could give a simple equation for the following situation.other than recursion plz.. occurrences :: Eq a => a -> [a] -> [a] --occurrences xs ys returns the number of times that xs occurs in ys thanks

2 1

Re: Type equivalency 2
by Ashley Yakeley 06 Jun '02

06 Jun '02

At 2002-06-06 03:38, Cagdas Ozgenc wrote: >Then either -> is not a type constructor, (->) is a type constructor. >or the concept of type >constructors has to be divided into two : consuming type constructors, and >producing type constructors. Type constructors can do anything they like with their arguments. Here are some of kind (* -> *): newtype Holds a = MkHolds a data Ignores a = MkIgnores newtype Wants a = MkWants (a -> Bool) data List a = MkPairList a (List a) | MkEmptyList data Maybe a = Just a | Nothing I don't think you can divide them up into two categories... -- Ashley Yakeley, Seattle WA

1 0

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by ��Ż�չЭ�� 06 Jun '02

06 Jun '02

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