Hello,

Here is the latest Caml Weekly News, week 21 to 28 January, 2003.

1) load modules by name
2) uname for Ocaml
3) Books on FP
4) New bug fix version of Camlimages library

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1) load modules by name
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Pietro Abate asked:

I'm trying to figure out how I can build a kind of associative list
to load a specific module at runtime. I've reread few old messages about
first-class modules and other oddities, but I've the sensation my
problem is easier.

I have a library (compiled), an application (compiled) and a bunch of
user defined modules (that are compiled as well, but these may be vary
in number). At the moment the application select the rigth module
statically regarding a command line argument. However this way I must
recompile my application everytime I add a new module.

What I'd like to do is reading all .cmo files (or .ml files and compile
them on the fly) in a directory and build a kind of assoc list with 
(name,module) and at runtime select the right module.

let's say that now I have

let algo = 
match command_line_option with
| "mod1" -> Module1.algo
| "mod2" -> Module2.algo
...
| _ -> failwith "module not defined"
in ...

but I'd rather have something like

let algo =
	try
		List.assoc "command_line_option" assoclist
	with Not_found -> failwith "Module not defined"
in ...

That would not require any recompilation of my application.

It would also nice to compile on the fly these modules...
I'm thinking of something like eval in perl...

is it possible ?

And Stefano Zacchiroli answered:

Yes, just use the Dynlink module.

You can find a great usage example in the O'Reilly book [1] (debian
package available in debian/unstable ocaml-book-{en,fr}).

Anyway, returning to your example you should have an association list
ref, say "algos", and you should use it as

  let algo =
    try
      List.assoc "command_line_option" !algos
   with Not_found -> failwith "Module not loaded"

Then you should have a set of .cmos that you should load using
'Dynlink.loadfile', each module should update the 'algos' association
list adding itself to it.

Hope this helps,
Cheers.

[1] http://caml.inria.fr/oreilly-book/html/

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2) uname for Ocaml
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Basile Starynkevitch announced:

If you need to call uname(2) from some Ocaml program you can steal my
tiny code in util.ml util.mli util_ml.c on

http://www2.poesia-filter.org:8000/cgi-bin/cvsweb.cgi/PoesiaSoft/PoesiaMonIcap/

I actually wish that uname(2) will be incorporated in the Unix module.

Following a discussion on how to capture the output of a system call,
Issac Trotts said:

You're right: it's shorter to say

  let sys_call cmd =
    let inc = Unix.open_process_in cmd in
    let buf = Buffer.create 16 in
    (try while true do Buffer.add_channel buf inc 1 done with _ -> ());
    close_in inc;
    Buffer.contents buf;;

Or we can break the call results into lines:

  let rec input_lines file =
    try
      let ln = input_line file in
      ln :: input_lines file
    with
      End_of_file -> [];;

  let sys_lines cmd =
    let pipe = Unix.open_process_in cmd in
    let lines = input_lines pipe in
    close_in f;
    lines;;

Sometimes it would be better to iterate a function over the lines:

  let sys_iter f cmd =
    let pipe = Unix.open_process_in cmd in
    (try while true do f (input_line pipe) done with _ -> ());
    close_in pipe;;

This can be used for things like

  sys_iter print_endline "ls";;

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3) Books on FP
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(Editor note: FP = Functional Programming)
Oliver Bandel asked:

I think about buying a book on FP-programming.

Is there a book, which can be recommended?

I know "The Craft of functional programming",
but after a while (since jumping from some
haskell-experiments to OCaml) have not read
further in it.

It's an interesting book, but too specific
focussed on haskell.

Are there more general books?
But I'm not a studied computer scientist, so
it's better if it is not too much specialized
mathematics and theory. It should be an introductional
book, but on an interesting level, which is
forcing the reader to explore practical problems.

Jocelyn Sérot said:

I would highly recommand Cousineau and Mauny's "The Functional Approach
to Programming".
(http://pauillac.inria.fr/cousineau-mauny/main.html ).
I haven't read the english version, but the french one is very well
written and shows IMHO a good
balance between theory and practice.

Mattias Waldau asked and Jocelyn Sérot answered:

>What did you think about the O'Reilly book on www.ocaml.org? 

Great book for doing "real" Ocaml programming (as opposed to learning).
But the focus is, imho, more on technical than on "fundamental" issues.

Personnaly, i use Cousineau and Mauny as a textbook when teaching
and the Oreilly as a reference book for my hacking.

Gleb Semenov proposed:

I can recommend the two books:

1. "Structure and Interpretation of Computer Programs", by Abelson,
    Sussman, and Sussman ("SICP", "Wizard book").
    http://mitpress.mit.edu/sicp/
    One of the bibles in lisp/scheme world.

2. Field, A.J. and Harrison, P.G.,
   "Functional Programming", Addison-Wesley, 1988.
   Good theoretical introduction in functional programming.
   Available from amazon.com (or at local bookstores
   which are selling used books).

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4) New bug fix version of Camlimages library
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Jun.Furuse announced:

Version 2.11 of the CamlImages library, by Jun Furuse, François
Pessaux, and Pierre Weis, is now available.

CamlImages is an image processing library, which provides to the
objective Caml programmer:

  ** basic functions for image processing and loading/saving various image
  file formats (hence providing a translation facility from format to format),

  ** an interface with the Caml graphics library allows to display
  images in the Graphics module screen and to mix them with Caml
  drawings,

  ** a freetype interface, integrated into the library:
  you can draw texts into images using any truetype fonts,

  ** a set of example programs, including gif animation, slide show, postscript
  converter to print images.

Version 2.11 is a bug fix release and does not contain majour changes.

Sources and documentation are available from:  

http://pauillac.inria.fr/camlimages/eng.htm

ftp://ftp.inria.fr/lang/caml-light/bazar-ocaml/camlimages-2.11.tgz 

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Alan Schmitt