Hi Bulat,
thank you very much for such a detailed reply!
I just started to study Haskell and it is my almost first big experience
with functional languages (except Emacs Lisp and Python). I enjoyed all
small exercises and started a bigger business writing a general utility.
you are my ideal client because we both speak Russian (but not here :) )
Da! :) Spasibo.
and both interested in large "real-world" applications :) download
the http://freearc.narod.ru/FreeArc-sources.tar.gz and enjoy - it's a
full of Russian comments and it's a real-world program that solves
many problems that you yet foresee :)
in particular, i also started with vision of my program (it's a
RAR-like archiver) as a sequence of transformations:
1) first, a command line translated into the program "job" - it's
actually business of GetOpt and not very differ from other language's
implementations
2) second, this job plus information about files on disk is translated
into the record of structure of archive being created
3) third, archive structure translated into the sequence of I/O
operations
but when i started to do the actual implementation, i realized that
such pure functional approach is nor appropriate and at the last end
i wrote the straight imperative program, just using the power of
Haskell language. moreover, in this process i added to the language
many imperative constructs that make imperative programming easier
I really trying to avoid imperative approach. I do have a terribly big
experience in imperative programming (by the way, you might know one
application that I made about 3 years ago. It is Uni-K Sensei for
windows). Now, I am breaking my previous habits just to think wider and
more effective.
However, I have a problem from the beginning. The utility get some file
and convert it to another format. It is a kind of small compiler. It
also accepts many parameters and behaves depending on them. The problem
is how to do this neat! How should I write my program to accept and
neatly work with options????
you can see my solution in Cmdline module - it's one of largest module
in my program. i don't like the GetOpt interface (it returns a list of
options what is unusable for high-speed application) so i implemented
Well, I do not care too much about high-speed. My main goal is to write
a prototype of the language that I am creating. It is a kind of
Domain-Specific language. I decided to start from a simple thing. A
converter of pgn files with chess notation to javascript to visualize
it. Just to have some practice.
my own option-processing routines, it's just about 50 lines long
(great demonstration of Haskell power!). all processed options are
record in one large record that is passed around all the program. if
you get accustomed to global variables, it's using in Haskell is
possible but that is not the best way. you can also use implicit
parameters (at least in hugs and ghc), but this again makes data
dependencies somewhat non-understandable
Thank you very much. I will see this approach as well. I am still pretty
concern of using records instead of lists.
btw, i suggest you to use WinHugs for debugging program and ghc for
final compilation. this makes faster development time together with
faster final executable. moreover, making your program compatible with
both environments is almost ensure that it will be compatible with
coming Haskell standard, Haskell-prime
Thanks again. I do not use Windows any more. I use Mac or different
Unices. I do use ghc everywhere I work with Haskell. For debugging I use
ghci. Well, and everything within GNU Emacs.
returning back to options parsing - there is an interesting
alternative to GetOpt (which is just mimics corresponding C module) -
it's a PescoCmd:
http://scannedinavian.org/~pesco/distfiles/pesco-cmdline-2.0.tgz
http://scannedinavian.org/~pesco/distfiles/pesco-cmdline-2.0.pdf
http://scannedinavian.org/~pesco/distfiles/pesco-cmdline-man-2.0.pdf
Thanks! Very interesting
i also recommend you to read several other real-world Haskell program
where you can steal more code and ideas:
http://postmaster.cryp.to/postmaster-2005-02-14.tar.gz
ftp://ftp.cse.unsw.edu.au/pub/users/dons/yi/yi-0.1.0.tar.gz
darcs (darcs get --partial http://www.abridgegame.org/repos/darcs/)
happs (darcs get --partial http://happs.org/HAppS)
Darcs was a little too complicated for me. Thank you for other links.
and one more interesting source of real-world approach to Haskell
programming:
http://www.haskell.org/haskellwiki/Hitchhikers_Guide_to_the_Haskell
Thank you very much, Bulat. Now I see why people say that haskell-cafe
is the best mail-list! :)
Anton Kulchitsky
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