[Caml-list] Printing text with holes

[Caml-list] Printing text with holes

[Martin Jambon]

Hello,

I am curious to know what people use to print long text written in a
natural language, and containing many holes, like dynamically generated
web pages.

Printf is not satisfying for this kind of task because the formatting
directives are far from the arguments: adding, removing or swapping
parameters in the text becomes really difficult with long text and several
arguments unless you make the text completely unreadable.

The solution I adopted some time ago is the following:

intead of this:

   printf "Hello %s %s! It is %i o'clock."
	first_name last_name time


we write:

   << Hello $first_name $last_name! It is $int{time} o'clock. >>



which is converted into

let _ =
  Pervasives.print_string "Hello ";
  Pervasives.print_string first_name;
  Pervasives.print_string " ";
  Pervasives.print_string last_name;
  Pervasives.print_string "! It is ";
  print_int time;
  Pervasives.print_string " o'clock."


Any function prefixed by print_ can be defined and used as a `format
specifier'.
It is also possible to pass several arguments to one function:
  << $x{arg1 arg2} >>
is equivalent to
  print_x arg1 arg2

but << ${"a" ^ "b"} >> becomes  print_string ("a" ^ "b")

<< $data.field >>            becomes  print_string data.field


Does anyone need this kind of approach?
Any better ideas?

I put my implementation here (it is quite ugly, I still ignore everything
about Camlp4):
  http://martin.jambon.free.fr/bazar/printfer.tar.gz


-- Martin


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Re: [Caml-list] Printing text with holes

[Christian Lindig]

On Mon, Sep 29, 2003 at 03:16:38PM +0200, Martin Jambon wrote:
> I am curious to know what people use to print long text written in a
> natural language, and containing many holes, like dynamically
> generated web pages.

I just like to point out two papers that you might find inspiring:


    Danvy, Olivier, Functional Unparsing, Journal of Functional
    Programming, 1998, 8(6) 621--625,

    Philip Wadler, A prettier printer. The Fun of Programming. A symposium
    in honour of Professor Richard Bird's 60th birthday Examination Schools,
    Oxford, 24-25 March 2003. 

-- Christian 

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Re: [Caml-list] Printing text with holes

[Benjamin Geer]

Martin Jambon wrote:
> I am curious to know what people use to print long text written in a
> natural language, and containing many holes, like dynamically generated
> web pages.

I'm writing a general-purpose template processor for Caml; an early 
release should be ready for download in a week or so.

Ben

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Re: [Caml-list] Printing text with holes

[Brian Hurt]

On Mon, 29 Sep 2003, Martin Jambon wrote:

> Hello,
> 
> I am curious to know what people use to print long text written in a
> natural language, and containing many holes, like dynamically generated
> web pages.

I agree.  I think printf is a horrible way to do output.  Reasons include, 
but are not limited to, the fact that you are basically creating a new 
"mini-language" (the formatting language) which has to be type checked 
etc. seperately from the main language, that the values being put into the 
string are listed far from their positions in the string (your problem) 
leading to missing parameters, parameters in the wrong order, etc.

> The solution I adopted some time ago is the following:

IMHO, this is certainly a better solution to the problem.  But it does 
need p4 (I think).

What might be even better is an output operator, ala C++.  Maybe something 
like:

let ( <$ ) chan str = output_string chan str; chan

This would allow you to do:
let _ = stdout <$ "Hello " <$ first_name <$ " " <$ last_name <$ "! It is "
<$ (string_of_int time) <$ " o'clock.\n";;

Not quite as clean, but close, and it doesn't require p4.

Brian


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Re: [Caml-list] Printing text with holes

[Jean-Marc EBER]

> 
> This would allow you to do:
> let _ = stdout <$ "Hello " <$ first_name <$ " " <$ last_name <$ "! It is "
> <$ (string_of_int time) <$ " o'clock.\n";;
> 
> Not quite as clean, but close, and it doesn't require p4.
> 

With "old" printf approach, you write something like:
let _ =
   printf "Hello %s %s! It is %i o'clock.\n" first_name last_name time

Matter of taste: I prefer the printf version.

More generally, I have found the printf approach (more precisely OCaml's 
Format 'magic' standard module) of incredible power and flexibility, if 
  (and only if :-) ) used consistently through *all* your program. This 
is especially true when you generate "big" documents, where you compose 
recursively many "nice" ways to pretty-print your result(s).

Jean-Marc Eber


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Re: [Caml-list] Printing text with holes

[Brian Hurt]

On Mon, 29 Sep 2003, Jean-Marc EBER wrote:

> With "old" printf approach, you write something like:
> let _ =
>    printf "Hello %s %s! It is %i o'clock.\n" first_name last_name time

It also allows you to do:

let _ = printf "Hello %s %s! It is %i o'clock.\n" name time

To detect this is a problem, the compiler has to not only parse Ocaml, it 
also has to parse printf format strings.

The one advantage that printf has is familiarity.  All of us who are old C 
programmers (and I fall into this category) know printf.  But that doesn't 
make it a good interface.

Brian


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Re: [Caml-list] Printing text with holes

[Pierre Weis]

> On Mon, 29 Sep 2003, Jean-Marc EBER wrote:
> 
> > With "old" printf approach, you write something like:
> > let _ =
> >    printf "Hello %s %s! It is %i o'clock.\n" first_name last_name time
> 
> It also allows you to do:
> 
> let _ = printf "Hello %s %s! It is %i o'clock.\n" name time

This is not well-typed and the error is properly spotted by the compiler:

# Printf.printf "Hello %s %s! It is %i o'clock.\n" name time;;
                                                        ^^^^   
This expression has type int but is here used with type string

> To detect this is a problem, the compiler has to not only parse Ocaml, it 
> also has to parse printf format strings.

Absolutely. This exactly similar to what the compiler does when
reading string constants in order to properly look for escapes, or
when it reads strings of digits to decide if it means an integer or a
floating point number.

As long as you realize that format strings are yet another kind of
primitive constants you easily admit that the compiler has to
type-check them. It is the usual compiler stuff, although a bit more
complex, since format string constants have complex types.

> The one advantage that printf has is familiarity.  All of us who are old C 
> programmers (and I fall into this category) know printf.  But that doesn't 
> make it a good interface.
> 
> Brian

You are absolutely right: good old C functions have not automatically
good old interfaces (for a counterexample just consider ioctl, malloc
and free, compared to their void equivalent in Caml, or longjump and
setjump compared with the nice try raise constructs). Conversely, we
must admit that good old C functions do not necessarily have a bad
interface, isn't it ?  (May I mention as an example the basic
arithmetic operators ?)

However, concerning printf, you should realize that the Caml printf
facility (or scanf, to mention another facility that uses format
strings) are not mere transpositions of their C equivalent. They have
powerful additional features (%a, %C, %S, %t for instance), their
typechecking is entirely static, their interface is much more in the
spirit of functional programming, and last but not least the kprintf
or kscanf versions of the basic primitives have no equivalent in C.

May I also mention specifically for printf the additional facility of
the Format module with its associated high-level pretty-printing
facilities that are completely and smoothly integrated into the format
strings mechanism ?

Concerning these powerful additions, I'm not sure that good old C
programmers always have a fluent knowledge of the kind of features our
Caml printf and scanf primitives provide.

Pierre Weis

INRIA, Projet Cristal, Pierre.Weis@inria.fr, http://pauillac.inria.fr/~weis/

PS: As an example, I should mention that the Caml scanf function is
powerful enough to allow the definition of a polymorphic list scanner
generator, that can be apply to any element specific scanner to
provide a scanner for lists of those elements' type: this is indeed
polymorphic higher-order scanning, well in the spirit of functional
programming, and I doubt you can easily obtain that with the C scanf
(nor program the Caml polymorphic list scanner with your good old C
scanf knowledge)...

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Re: [Caml-list] Printing text with holes

[Richard Jones]

On Mon, Sep 29, 2003 at 10:48:02PM +0200, Pierre Weis wrote:
> However, concerning printf, you should realize that the Caml printf
> facility (or scanf, to mention another facility that uses format
> strings) are not mere transpositions of their C equivalent. [...] their
> typechecking is entirely static,

On this one small point, people who have been using gcc have had
type safe printf/scanf for at least the last 15 years.

Rich.

-- 
Richard Jones. http://www.annexia.org/ http://freshmeat.net/users/rwmj
Merjis Ltd. http://www.merjis.com/ - all your business data are belong to you.
MONOLITH is an advanced framework for writing web applications in C, easier
than using Perl & Java, much faster and smaller, reusable widget-based arch,
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Re: [Caml-list] Printing text with holes

[Fred Yankowski]

On Mon, Sep 29, 2003 at 10:52:34PM +0100, Richard Jones wrote:
> On this one small point, people who have been using gcc have had
> type safe printf/scanf for at least the last 15 years.

What do you mean?  Compiling the following with gcc 2.95.4 and
executing it causes a seg fault on my Linux 2.4.20 system:

	main() {  printf("%s", 'a'); }

-- 
Fred Yankowski      fred@ontosys.com           tel: +1.630.879.1312
OntoSys, Inc	    PGP keyID: 7B449345        fax: +1.630.879.1370
www.ontosys.com     38W242 Deerpath Rd, Batavia, IL 60510-9461, USA

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Re: [Caml-list] Printing text with holes

[Daniel M. Albro]

	I assume he means that it won't compile if you use
"gcc -Wall -Werror".

						- Dan Albro

On Mon, 2003-09-29 at 15:07, Fred Yankowski wrote:
> On Mon, Sep 29, 2003 at 10:52:34PM +0100, Richard Jones wrote:
> > On this one small point, people who have been using gcc have had
> > type safe printf/scanf for at least the last 15 years.
> 
> What do you mean?  Compiling the following with gcc 2.95.4 and
> executing it causes a seg fault on my Linux 2.4.20 system:
> 
> 	main() {  printf("%s", 'a'); }
-- 
Daniel M. Albro <albro@humnet.ucla.edu>

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Re: [Caml-list] Printing text with holes

[Richard Jones]

On Mon, Sep 29, 2003 at 03:14:31PM -0700, Daniel M. Albro wrote:
> 
> 	I assume he means that it won't compile if you use
> "gcc -Wall -Werror".

Indeed. Which for all practical purposes means it's type safe.

Rich.

-- 
Richard Jones. http://www.annexia.org/ http://freshmeat.net/users/rwmj
Merjis Ltd. http://www.merjis.com/ - all your business data are belong to you.
 All new technology is irrelevant until it is taken up by the public.

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Re: [Caml-list] Printing text with holes

[Matthieu Sozeau]

On Tuesday 30 September 2003 00:07, Fred Yankowski wrote:
> On Mon, Sep 29, 2003 at 10:52:34PM +0100, Richard Jones wrote:
> > On this one small point, people who have been using gcc have had
> > type safe printf/scanf for at least the last 15 years.
>
> What do you mean?  Compiling the following with gcc 2.95.4 and
> executing it causes a seg fault on my Linux 2.4.20 system:
>
> 	main() {  printf("%s", 'a'); }

gcc is permissive by default, use -Wall !
-- 
Matthieu Sozeau
www: http://mattam.ath.cx

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Re: [Caml-list] Printing text with holes

[Brian Hurt]

On Mon, 29 Sep 2003, Fred Yankowski wrote:

> On Mon, Sep 29, 2003 at 10:52:34PM +0100, Richard Jones wrote:
> > On this one small point, people who have been using gcc have had
> > type safe printf/scanf for at least the last 15 years.
> 
> What do you mean?  Compiling the following with gcc 2.95.4 and
> executing it causes a seg fault on my Linux 2.4.20 system:
> 
> 	main() {  printf("%s", 'a'); }
> 
> 

It spits out warnings, not errors, if you add the -Wformat (or, 
alternatively, the -Wall) option to your compile flags.

Brian


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Re: [Caml-list] Printing text with holes

[Brian Hurt]

On Mon, 29 Sep 2003, Pierre Weis wrote:

> > On Mon, 29 Sep 2003, Jean-Marc EBER wrote:
> > 
> > > With "old" printf approach, you write something like:
> > > let _ =
> > >    printf "Hello %s %s! It is %i o'clock.\n" first_name last_name time
> > 
> > It also allows you to do:
> > 
> > let _ = printf "Hello %s %s! It is %i o'clock.\n" name time
> 
> This is not well-typed and the error is properly spotted by the compiler:

Because the compiler understands printf strings as a special case.  I do 
not know of a way I could write printf in standard Ocaml.  You need 
specialized compiler support.  Which makes it very difficult to extend, at 
best.  You basically end up mucking about in p4.

At heart, printf is doing two seperate jobs.  First, it's formating binary 
data (integers, floating points, etc) into there textual/formatted 
representations.  And second, they are outputing said formatted strings.  
These are two completely different jobs which should be done by different 
blocks of code.  Java started recognizing this when they seperated the 
formatting objects from the i/o objects.  And for all of it's limitations, 
and Java I/O has it's limitations, I think it hit upon a better solution 
than printf.  Of course, Java's I/O model isn't radical or new, as any 
Unix shell programmer will tell you.

> Absolutely. This exactly similar to what the compiler does when
> reading string constants in order to properly look for escapes, or
> when it reads strings of digits to decide if it means an integer or a
> floating point number.

Printf is at a completely different level of complexity than simply 
escaping strings.  Escaping strings (and differentiating integers from 
floats) can be done entirely in the lexer.

I've actually written printf implementations.  Even ignoring "amusing" 
complications like locales and floating point numbers, they are not simple 
beasts.  

> You are absolutely right: good old C functions have not automatically
> good old interfaces (for a counterexample just consider ioctl, malloc
> and free, compared to their void equivalent in Caml, or longjump and
> setjump compared with the nice try raise constructs). Conversely, we
> must admit that good old C functions do not necessarily have a bad
> interface, isn't it ?  (May I mention as an example the basic
> arithmetic operators ?)

There is very little in the standard C libraries I would consider "good" 
outside of C.  Primarily because (IMHO) there is very little in the 
standard C libraries.  Nor is C particularly noted for it's ease of 
manipulation of strings and I/O.  About all I ever hear anyone say about C 
and text manipulation is that it's better than FORTRAN, which qualifies as 
damning with faint praise.  Now, the Unix command line, *there* is an 
environment good for text processing.  Good enough that it's been stolen 
in one way or another at least twice (Java and Perl- Perl doing a more 
thorough job of stealing, while Java stole the basic concepts).

Here's how it would work- you would have three categories of objects.  
The first category would be sources and sinks.  A source is an object with
a read function, a sink is an object with a write function.  These objects 
would represent files and strings and network sockets etc.  The second 
category is filters.  A filter looks to the outside just like a source or 
a sink, but instead of being a final destination it just does something to 
the data and then passes it along.  A classic example of a filter is an 
encryption object- looks just like a sink, but when you write data to it, 
it encrypts the data and then writes it in turn to another sink (which may 
be another filter).  The third category of objects is formating 
objects or functions.  These take binary data and turn them into string 
representations.  A classic example here is string_of_int.

Note that since I'm working within the language, all the parts are easily 
extensible and replaceable.

Brian


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Re: [Caml-list] Printing text with holes

[David Brown]

On Mon, Sep 29, 2003 at 11:40:21PM -0500, Brian Hurt wrote:

> At heart, printf is doing two seperate jobs...

I've done considerable programming both in languages that have
printf-style formatting (checked and unchecked), as well as languages
that require operators or such to build up formatting.  Any time I've
wanted to output something, I have one of two responses, depending on
the language:

  - Grumble, grumble, grumble.
  - Just write it.

You can probably guess which is which.  That ocaml has been able to
integrate printf formatting in a type-safe way is truly amazing, and to
me one of the things that makes ocaml a wonderful language.

True, it isn't universally extensibly, but it is a lot more so than most
people think.

Dave

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Re: [Caml-list] Printing text with holes

[Martin Jambon]

On Mon, 29 Sep 2003, Jean-Marc EBER wrote:

> >
> > This would allow you to do:
> > let _ = stdout <$ "Hello " <$ first_name <$ " " <$ last_name <$ "! It is "
> > <$ (string_of_int time) <$ " o'clock.\n";;
> >
> > Not quite as clean, but close, and it doesn't require p4.
> >
>
> With "old" printf approach, you write something like:
> let _ =
>    printf "Hello %s %s! It is %i o'clock.\n" first_name last_name time
>
> Matter of taste: I prefer the printf version.
>
> More generally, I have found the printf approach (more precisely OCaml's
> Format 'magic' standard module) of incredible power and flexibility, if
>   (and only if :-) ) used consistently through *all* your program. This
> is especially true when you generate "big" documents, where you compose
> recursively many "nice" ways to pretty-print your result(s).

Yes, printf is OK if you don't have to do many substitutions in one time.
This is probably the case most of the time for printing structured output.
But printing human-readable text has a strong constraint: it must fit on
one 2-dimensional page, with a nice appearance and few empty parts.
This is why the programmer likes to have an overview of the
output. Having an overview of the output (its shape) is totally
useless if you need to print tree-like data to be read by a machine.
Just imagine that we want to use a kind of LaTeX or HTML formatting style
from Caml, or find some better solution :-)

In our situation, the problem is that the efforts required for a
modification (let's say the insertion of a new variable) grow with the
size of the output. This is even harder when all your variables have the
same type and if there is more than one screen between the format
specifier and the variable.

Well, I just extracted some code from one of my CGI programs.
Here, the purpose is to print one line of an HTML table, where one column
should appear in bold face (using arrays containing strings "" or "<b>" or
"</b>").
Here is the code:

let print_binary_patch id bb be ranking p =
  let volume1 = p.patch_1.volume in
  let volume2 = p.patch_2.volume in
  let vol_percentage1 = p.patch_1.relative_volume *. 100. in
  let vol_percentage2 = p.patch_2.relative_volume *. 100. in

  let print_option = function
      None -> ()
    | Some s -> << ($s) >> in
  <<
<tr>
  <td>$int{ranking} $matched_tags{p}
  [<a href="$sumo_focus_url?id=$id&index=$int{p.patch_global.patch_number}&quick=false" target=_blank>View</a>]
  [<a href="$sumo_focus_url?id=$id&index=$int{p.patch_global.patch_number}&quick=true" target=_blank>Quick view</a>]</td>
  <td>${bb.(1)}$g{p.patch_global.patch_size}${be.(1)}</td>
  <td>${bb.(2)}$r1{vol_percentage1}% ($r1{volume1})${be.(2)}</td>
  <td>${bb.(3)}$r2{vol_percentage2}% ($r2{volume2})${be.(3)}</td>
  <td>${bb.(4)}$int{p.patch_1.pdb_group_number}${be.(4)}</td>
  <td>${bb.(5)}$int{p.patch_2.pdb_group_number}${be.(5)}</td>
  <td>${bb.(6)}$f3{p.patch_global.patch_sumo_score}${be.(6)}</td>
</tr>
>>

This does not look very beautiful, but for me it is important to have a
compact representation where one line of source code produces not less
than one line of output. This allows to have a global overview of the
output without having to run the program.
The above piece of code has 28 holes... that we must be able to modify at
any time, just because we don't print all the data.



I would like to thank everyone for expressing their opinion on the
subject!


-- Martin

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Re: [Caml-list] Printing text with holes

[Pierre Weis]

[...]
> Well, I just extracted some code from one of my CGI programs.
> Here, the purpose is to print one line of an HTML table, where one column
> should appear in bold face (using arrays containing strings "" or "<b>" or
> "</b>").
> Here is the code:
> 
> let print_binary_patch id bb be ranking p =
>   let volume1 = p.patch_1.volume in
>   let volume2 = p.patch_2.volume in
>   let vol_percentage1 = p.patch_1.relative_volume *. 100. in
>   let vol_percentage2 = p.patch_2.relative_volume *. 100. in
> 
>   let print_option = function
>       None -> ()
>     | Some s -> << ($s) >> in
>   <<
> <tr>
>   <td>$int{ranking} $matched_tags{p}
>   [<a href="$sumo_focus_url?id=$id&index=$int{p.patch_global.patch_number}&quick=false" target=_blank>View</a>]
>   [<a href="$sumo_focus_url?id=$id&index=$int{p.patch_global.patch_number}&quick=true" target=_blank>Quick view</a>]</td>
>   <td>${bb.(1)}$g{p.patch_global.patch_size}${be.(1)}</td>
>   <td>${bb.(2)}$r1{vol_percentage1}% ($r1{volume1})${be.(2)}</td>
>   <td>${bb.(3)}$r2{vol_percentage2}% ($r2{volume2})${be.(3)}</td>
>   <td>${bb.(4)}$int{p.patch_1.pdb_group_number}${be.(4)}</td>
>   <td>${bb.(5)}$int{p.patch_2.pdb_group_number}${be.(5)}</td>
>   <td>${bb.(6)}$f3{p.patch_global.patch_sumo_score}${be.(6)}</td>
> </tr>
> >>
> 
> This does not look very beautiful, but for me it is important to have a
> compact representation where one line of source code produces not less
> than one line of output. This allows to have a global overview of the
> output without having to run the program.
> The above piece of code has 28 holes... that we must be able to modify at
> any time, just because we don't print all the data.
> 
> I would like to thank everyone for expressing their opinion on the
> subject!
> 
> -- Martin

In this case, I surely would use a template file, read the template in
memory, build the substitution function (with a hash table ?) for the
dollar identifiers and then use string substitution with
Buffer.add_subtitute to produce the output in a Buffer.t value.

Hope this helps,

Pierre Weis

INRIA, Projet Cristal, Pierre.Weis@inria.fr, http://pauillac.inria.fr/~weis/


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Re: [Caml-list] Printing text with holes

[skaller]

On Tue, 2003-09-30 at 04:57, Martin Jambon wrote:
> On Mon, 29 Sep 2003, Jean-Marc EBER wrote:

>   <<
> <tr>
>   <td>$int{ranking} $matched_tags{p}
>   [<a href="$sumo_focus_url?id=$id&index=$int{p.patch_global.patch_number}&quick=false" target=_blank>View</a>]
>   [<a href="$sumo_focus_url?id=$id&index=$int{p.patch_global.patch_number}&quick=true" target=_blank>Quick view</a>]</td>
>   <td>${bb.(1)}$g{p.patch_global.patch_size}${be.(1)}</td>
>   <td>${bb.(2)}$r1{vol_percentage1}% ($r1{volume1})${be.(2)}</td>
>   <td>${bb.(3)}$r2{vol_percentage2}% ($r2{volume2})${be.(3)}</td>
>   <td>${bb.(4)}$int{p.patch_1.pdb_group_number}${be.(4)}</td>
>   <td>${bb.(5)}$int{p.patch_2.pdb_group_number}${be.(5)}</td>
>   <td>${bb.(6)}$f3{p.patch_global.patch_sumo_score}${be.(6)}</td>
> </tr>
> >>
> 
> This does not look very beautiful, but for me it is important to have a
> compact representation where one line of source code produces not less
> than one line of output. 

You have it easy. You're mainly concerned with nice line breaks.
Consider if you were formatting a plain text table and needed
to have a view of *column* positions. That's where you start
renaming all your variables to exactly 4 letters so you can check
that things line up vertically .. :)

I have this kind of problem (vaguely) in Felix and the only
solution I found was "suck it and see".

[I'm generating C++ and I want the output layout to look nice ..]




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Re: [Caml-list] Printing text with holes

[Martin Jambon]

On 30 Sep 2003, skaller wrote:

> You have it easy. You're mainly concerned with nice line breaks.
> Consider if you were formatting a plain text table and needed
> to have a view of *column* positions. That's where you start
> renaming all your variables to exactly 4 letters so you can check
> that things line up vertically .. :)
>
> I have this kind of problem (vaguely) in Felix and the only
> solution I found was "suck it and see".
>
> [I'm generating C++ and I want the output layout to look nice ..]

So we need some kind of WYSIWYG editors.
Imagine your source code contains "special regions", that you can edit
using a custom WYSIaWYG editor (what you see is almost what you get),
called from your favorite text editor.
Maybe it would be enough to specify line-breaking keywords and tabulation
marks to generate a minimalist WYSIaWYG editor.

(*BEGIN { tabs = [Before "<td>"; Before "<th>"; Before "</tr>"];
          newlines = [After "<br>"; After "</tr>"] } *)
<table>
 <tr><th>$header_number_1</th><th>$short</th></tr>
 <tr><td>$x</td><td>$y</td></tr>
</table>
(*END *)

would be displayed as:

 <table>
  <tr><th>$header_number_1</th><th>$short</th></tr>
  <tr><td>$x</td>              <td>$y</td>    </tr>
 </table>

(+ syntax highlighting for fake spaces, insertions, keywords, ...)



-- Martin


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Re: [Caml-list] Printing text with holes

[Richard Jones]

On Mon, Sep 29, 2003 at 11:39:32AM -0500, Brian Hurt wrote:
> On Mon, 29 Sep 2003, Martin Jambon wrote:
> 
> > Hello,
> > 
> > I am curious to know what people use to print long text written in a
> > natural language, and containing many holes, like dynamically generated
> > web pages.
> 
> I agree.  I think printf is a horrible way to do output.  Reasons include, 
> but are not limited to, the fact that you are basically creating a new 
> "mini-language" (the formatting language) which has to be type checked 
> etc. seperately from the main language, that the values being put into the 
> string are listed far from their positions in the string (your problem) 
> leading to missing parameters, parameters in the wrong order, etc.

Well it may not be theoretically any good, but practically printf is
immensely usable.

Rich.

-- 
Richard Jones. http://www.annexia.org/ http://freshmeat.net/users/rwmj
Merjis Ltd. http://www.merjis.com/ - all your business data are belong to you.
"My karma ran over your dogma"

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Re: [Caml-list] Printing text with holes

[Pierre Weis]

Hello,

> I am curious to know what people use to print long text written in a
> natural language, and containing many holes, like dynamically generated
> web pages.
[...]
> Does anyone need this kind of approach?
> Any better ideas?
> 
> I put my implementation here (it is quite ugly, I still ignore everything
> about Camlp4):
>   http://martin.jambon.free.fr/bazar/printfer.tar.gz

Many people use the same approach with dollars. In the 3.07 release of
Objective Caml there is some support to easily obtain such a feature:
in the interface of the module Buffer, we find

val add_substitute : t -> (string -> string) -> string -> unit
(** [add_substitute b f s] appends the string pattern [s] at the end
   of the buffer [b] with substitution.
   The substitution process looks for variables into
   the pattern and substitutes each variable name by its value, as
   obtained by applying the mapping [f] to the variable name. Inside the
   string pattern, a variable name immediately follows a non-escaped
   [$] character and is one of the following:
   - a non empty sequence of alphanumeric or [_] characters,
   - an arbitrary sequence of characters enclosed by a pair of
   matching parentheses or curly brackets.
   An escaped [$] character is a [$] that immediately follows a backslash
   character; it then stands for a plain [$].
   Raise [Not_found] if the closing character of a parenthesized variable
   cannot be found. *)

This may be used to create strings with $identifiers to expand in them.

Hope this helps,

Pierre Weis

INRIA, Projet Cristal, Pierre.Weis@inria.fr, http://pauillac.inria.fr/~weis/


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Re: [Caml-list] Printing text with holes

[Karl Zilles]

Martin Jambon wrote:
> Hello,
> 
> I am curious to know what people use to print long text written in a
> natural language, and containing many holes, like dynamically generated
> web pages.
> 

I just used HereDoc to create a set of web pages, and found it pleasant 
to work in.

I used his old codebase, instead of the alpha version, since it looks 
like the alpha version hasn't been touched in 2 years.

http://www.eleves.ens.fr/home/frisch/soft.html#HereDoc

He has a syntax like yours:

<< Hello, $firstname $lastname. >>

or

<< I am $$ string_of_int age $$ years old >>

He doesn't appear to have any syntactic sugar for conversions.  Which 
wasn't a problem.

He has constructs for creating loops, and the ability to include 
templates from other files.

He's also abstracted out the printing so that you can tell it where you 
want to send the generated text.

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Re: [Caml-list] Printing text with holes

[Pierre Weis]

> Martin Jambon wrote:
> > Hello,
> > 
> > I am curious to know what people use to print long text written in a
> > natural language, and containing many holes, like dynamically generated
> > web pages.

I just use htmlc, which is simple and efficient:

  http://pauillac.inria.fr/htmlc/

It uses $identifiers as you suggested, + some Server Side Includes
expansions, + local environment definition facilities, + what you
would like to add to it in the future :)

Here is a brief excerpt of the Changes file:

1.20 (Documents environment variables expansion)
----
 - Inside documents variables of the form $X, $(X), or ${X} are
   considered to be bound in the Htmlc's global environment hash table
   and expanded as their corresponding string associated value.
 - New -e argument to load environment files that set up Htmlc's
   global environment table. Environment files are list of lines
   that contain a variable name and an associated string (following
   Caml' lexical conventions).
 - New server side directive: the line
   <!--#include environment="filename"-->
   in a document loads environment file ``filename'' and enriches the
   global environment accordingly.
 - New -s compilation flag to expand .shtml files into .html files.

1.10 (User's environment variables expansion)
----
 - Throughout documents passed to htmlc, tags of the form <$X>
   are considered to reference the variable X in the user's
   gloabal environment: <$HOME> is thus replaced by the string
   representation of the user's HOME directory.
   (This expansion mechanism is disabled when including verbatim
   files).

Hope this helps,

Pierre Weis

INRIA, Projet Cristal, Pierre.Weis@inria.fr, http://pauillac.inria.fr/~weis/


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Re: [Caml-list] Printing text with holes

[Jean-Christophe Filliatre]

 > > Martin Jambon wrote:
 > > > Hello,
 > > > 
 > > > I am curious to know what people use to print long text written in a
 > > > natural language, and containing many holes, like dynamically generated
 > > > web pages.

I use my own HTML pre-processor, yamlpp, available at

	http://www.lri.fr/~filliatr/yamlpp.en.html

which is no more than a 130 lines long ocamllex program.

-- 
Jean-Christophe

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