\input texinfo   @c -*-texinfo-*-

@c %**start of header
@setfilename templates_parser.info
@settitle Templates Parser User's Guide
@setchapternewpage off
@syncodeindex fn cp

@iftex
@afourpaper
@end iftex

@c ----------------------------------------- MACRO

@c Macro used for all Templates_Parser examples
@c No cartouche on HTML as this is part of the css
@macro TPEXP{TXT}
@ifhtml
@smallexample
@group
\TXT\
@end group
@end smallexample
@end ifhtml
@ifnothtml
@cartouche
@smallexample
@group
\TXT\
@end group
@end smallexample
@end cartouche
@end ifnothtml
@end macro

@c ----------------------------------------- END MACRO

@titlepage

@title Templates Parser User's Guide
@subtitle Date: @today{}
@author AdaCore

@sp 1
@url{http://libre.act-europe.fr/aws}

@vskip 0pt plus 1filll

@page

Copyright @copyright{} 1999-2004, Pascal Obry

Copyright @copyright{} 2005-2010, AdaCore

@*

This document may be copied, in whole or in part, in any form or by any
means, as is or with alterations, provided that (1) alterations are clearly
marked as alterations and (2) this copyright notice is included
unmodified in any copy.

@end titlepage

@ifhtml
@c title page for the HTML documentation
@html
<font size="+2">
<p>Document revision level $Revision: 163211 $
<p>Date: @today{}
<p>AdaCore
</font>

<font size="+1">
<p>@url{http://libre.act-europe.fr/aws}
</font>

@page
@end html
@end ifhtml
@finalout

@contents

@ifinfo
@node Top
@top Templates Parser

@menu
* Introduction::
* Tags::
* Template statements::
* Macros::
* Other services::
* Templates_Parser API Reference::
* Index::
@end menu
@end ifinfo

@c ----------------------------------------------------------------------
@node Introduction
@chapter Introduction
@c ----------------------------------------------------------------------

@noindent
The templates parser package has been designed to parse files and to
replace some specific tags into these files by some specified values.

@noindent
The main goal was to ease the development of Web servers. In CGI
(@i{Common Gateway Interface}) mode you have to write the HTML page in
the program (in Ada or whatever other languages) by using some specific
libraries or by using only basic output functions like Ada @code{Put_Line} for
example. This is of course not mandatory but by lack of a good library
every Web development end up doing just that.

@noindent
The main problems with this approach are:

@itemize @bullet

@item It is painful to have to recompile the program each time you have
a slight change to do in the design (center an image, change the border
width of a table...)

@item You have the design and the program merged together. It means that
to change the design you must know the Ada language. And to change the
Ada program you need to understand what is going on with all these
inline HTML command.

@item You can't use the nice tools to generate your HTML.

@end itemize

@noindent
With the templates parser package these problems are gone. The code and
the design is @b{completely} separated. This is a very important
point. PHP or JSP have tried this but most of the time you have the
script embedded into the Web template. And worst you need to use another
language just for your Web development.

@itemize @bullet

@item The HTML page is separated from the program code. Then you can
change the design without changing the code. Moreover when you fix the
code you don't have to handle all the specific HTML output. And you do
not risk to break the design.

@item It is easier to work on the design and the program at the same time
using the right people for the job.

@item It reduces the number of @i{edit/build/test} cycles. Writing HTML
code from a program is error prone.

@item It is possible to use standard tools to produce the HTML.

@item You don't have to learn a new language.

@item The script is Ada, so here you have the benefit of all the Ada power.

@end itemize

@noindent
In fact, the Ada program now simply computes some values, gets some data
from a database or whatever and then calls the templates parser to output
a page with the data displayed. To the templates parser you just pass
the template file name and an associative table.

@noindent
It is even more convenient to have different displays with the same set
of data. You just have to provide as many templates as you like.

@c ----------------------------------------------------------------------
@node Tags
@chapter Tags
@c ----------------------------------------------------------------------

@menu
* Tags in template files::
* Translations::
* Discrete Boolean Composite values::
* Filters::
* Attributes::
* Predefined tags::
* Dynamic tags::
@end menu

@c -----------------------------------------------------------------------
@node Tags in template files
@section Tags in template files
@c -----------------------------------------------------------------------

@noindent
A tag is a string found in the template page and surrounded by a specific set
of characters. The default is @b{@@_} at the start and @b{_@@} at the
end of the tag. This default can be changed using @code{Set_Tag_Separators}
routine, @pxref{Templates_Parser API Reference}. Note that it must be changed
as the first API call and should not be changed after that.

The tag will be replaced by a value specified in the Ada code.
In this context, the role of the Ada code is therefore to prepare what is
known as a translation, and then pass it to the templates parser, along with
the name of the template file to parse. This results in an expanded version
of the templates file, where all tags have been replaced by the value given
in the Ada code.

Let's start with a simple example. Here is the contents of the file
@file{demo.tmplt}, which is a very basic template file:

@include demo.tmplt.texi

@noindent
On its own, this template has little interest. However, it is used from some
Ada code similar to the following @file{demo.adb} file:

@include demo.adb.texi

@noindent
Compile this program, link with the templates parser, and when you run it,
the output will be:

@include demo.adb.res

@noindent
As you can imagine, this is a bare bone example. More complex structures are
of course possible. One thing to note, though, is that the template file
requires no Ada knowledge for editing, and is strongly related to your
application domain. One of the main usage for such templates is to generate
web pages. This can be done by a designer that knows nothing of how your
Ada code works. But you can use templates in other domains, including to
generate Ada code.

@c ----------------------------------------------------------------------
@node Translations
@section Translations
@c ----------------------------------------------------------------------

@noindent
In your Ada code, you can associate one or more values with a name, and
then reference that name in the template file as we just saw above.

Associating the value(s) with the name is done through one of the @code{Assoc}
constructors, @pxref{Templates_Parser API Reference}. Ada's overloading
resolution mechanism will take care of calling the appropriate constructor
automatically.

These associations are then grouped into a dictionary. This dictionary
is passed along with the name of the template file to the @code{Parse}
routine itself, which generates the final expanded representation of the
template. In fact, you will almost never have to manipulate an association
directly, since as soon as it is created you store it in the dictionary.

There are two types of dictionaries in the templates parser:

@table @code

@item Translate_Table
@cindex Translate_Table

This is an array of associations. If you know the exact number of
associations when you write your code, this will generally provide
a very readable code. The array can be initialized as soon as it is
declared.

@TPEXP{
  @b{declare}
     T : @b{constant} Translate_Table :=
       (1 => Assoc ("NAME1", Value1),
        2 => Assoc ("NAME2", Value2));
  @b{begin}
     Put_Line (Parse ("demo.tmplt", T));
  @b{end};}

@item Translate_Set
@cindex Translate_Set

If, on the other hand, you do not know statically the number of
associations, it is generally a lot more flexible to use another type
of dictionary, which isn't limited in size. It is also better to use
this type of dictionary if you need extra code to compute the values.

@TPEXP{
  @b{declare}
     T : Translate_Set
  @b{begin}
     Insert (T, Assoc ("NAME1", Value1));
     Insert (T, Assoc ("NAME2", Value2));
  @b{end};}

@end table

@noindent
Internally, the templates parser will always convert all dictionaries
to a @code{Translate_Set}, which is much more efficient when we need to
look values up.

@c ----------------------------------------------------------------------
@node Discrete Boolean Composite values
@section Discrete, Boolean and Composite values
@c ----------------------------------------------------------------------

@noindent
As we just saw, the values by which a tag is replaced must be provided
by the Ada code. Such values can be provided in different formats,
depending on the intended use.

The three kinds of tags are @b{discrete}, @b{Boolean} and @b{composite}
tags. These are all ways to associate one or more value to a name, which
is the name used in the template file.

@table @b

@item discrete values
@cindex Tag, discrete
This represents a single value associated with a name. The types of value
currently supported are String, Unbounded_String and Integer.

@TPEXP{
    Insert (T, Assoc ("NAME", 2));
 Insert (T, Assoc ("NAME", "VALUE"));}

@item Boolean values
@cindex Tag, Boolean
These are similar to discrete values. However, they are more convenient
to manipulate within @code{@@@@IF@@@@} statements in the template. When
outside an @code{IF} statement, such values are represented as TRUE or
FALSE.

@TPEXP{Insert (T, Assoc ("NAME", True));}

@item composite values
@cindex Tag, composite
A composite tag is a variable which contains a set of values. In terms of
programming languages, these would generally be called vectors. Since each
value within that can itself be a composite tag, you can therefore build
multi-dimensional arrays.

These kind of variables will be used with the @code{TABLE} tag statement
@pxref{TABLE statement}. Outside a table statement, the tag is
replaced by all values concatenated with a specified separator. See
@code{Set_Separator} routine. Such tag are variables declared in the
Ada program a @code{Templates_Parser.Tag} type.

There are many overloaded constructors to build a composite tags (see "+"
operators).  The "+" operators are used to build a Tag item from
standard types like String, Unbounded_String, Character, Integer and
Boolean.

To add items to a Tag many overloaded operators are provided (see
"&" operators). The "&" operators add one item at the start or the end
of the tag. It is possible to directly add String, Unbounded_String,
Character, Integer and Boolean items using one of the overloaded operator.

A tag composed of only Boolean values TRUE or FALSE is called a
Boolean composite tag. This tag is to be used with a @code{IF} tag statement
inside a @code{TABLE} tag statement.

It is possible to build a composite tag having any number of nested
level. A vector is a composite tag with only one level, a matrix is a
composite tag with two level (a Tag with a set of vector tag).

Two aliases exists for composite tags with one or two nested level,
they are named @code{Vector_Tag} and @code{Matrix_Tag}. In the suite
of the document, we call @i{vector tag} a tag with a single nested
level and @i{matrix tag} a tag with two nested level.

@TPEXP{
   @i{--  Building a composite tag}
   @i{--  Then add it into a translate set}
   @b{declare}
     V : Tag;
     T : Translate_Set;
   @b{begin}
     @b{for} Index @b{in} 1 .. 10 @b{loop}
        V := V & I;
     @b{end loop};
     Insert (T, Assoc ("VECTOR", V));
   @b{end};}

@end table

@c --------------------------------------------------------------------------
@node Filters
@section Filters
@cindex Filters
@c --------------------------------------------------------------------------

@menu
* Predefined filters::
* User defined filters::
@end menu

@noindent
Within the template file, functions can be applied to tags. Such functions
are called @code{filters}. These filters might require one or more
parameters, see the documentation for each filter.

The syntax is:

@TPEXP{
@code{@@_[[FILTER1_NAME[(parameter)]:]FILTER2_NAME[(parameter)]:]SOME_VAR_@@}.
}

When multiple filters are associated to a tag, they are evaluated from right
to left. In the example above, @code{FILTER1_NAME} is applied to the result
of applying @code{FILTER2_NAME} to @code{SOME_VAR}.

Remember that one of the goals in using templates is to remove as much
hard-coded information from the actual Ada source, and move it into easily
editable external files. Using filters is a convenient way to give the template
designer the power to specify the exact output he wants, even without changing
the Ada code. For instance, imagine that one suddenly decides that some
names should be capitalized in a template. There are two solutions to such
a change in design:

@itemize @bullet
@item Modify the Ada code to capitalize strings before storing them in
a tag variable. What if, in the template, we need the name once capitalized,
and once with its original casing ? This means the Ada code would have to
create two tags.

@item Modify the template itself, and use a filter. A single tag is required
on the Ada side, which doesn't even have to be changed in fact. The template
would for instance become:

@TPEXP{@@_CAPITALIZE:VAR_@@ : constant String := "@@_VAR_@@";}
@end itemize

The templates parser comes with a number of predefined filters, that can be
used in various situations. Some of these are highly specialized, but most of
them are fairly general. You can also define your own filters, adapted to
specific needs you might have.

Here are some more examples using the predefined filters:
@TPEXP{If VAR is set to "@i{vector_tag}", ONE to "1" and TWO to "2" then:

@@_VAR_@@                                   ->  vector_tag
@@_UPPER:VAR_@@                             ->  VECTOR_TAG
@@_CAPITALIZE:VAR_@@                        ->  Vector_Tag
@@_EXIST:VAR_@@                             ->  TRUE
@@_UPPER:REVERSE:VAR_@@                     ->  GAT_ROTCEV
@@_MATCH(VEC.*):UPPER:VAR_@@                ->  TRUE
@@_SLICE(1..6):VAR_@@                       ->  vector
@@_REPLACE(([^_]+)):VAR_@@                  ->  vector
@@_REPLACE(([a-z]+)_([a-z]+)/\\2_\\1):VAR_@@  ->  tag_vector
@@_"+"(TWO):ONE_@@                          ->  3
@@_"-"(TWO):ONE_@@                          ->  -1}

@c ----------------------------------------------------------------------------
@c -- Predefined filters
@c ----------------------------------------------------------------------------

@node Predefined filters
@subsection Predefined filters

Here is the complete list of predefined filters that come with the templates
parser.

@table @code

@item "+"(@i{N}) or ADD(@i{N})
@cindex Filter, "+"

Add N to variable and return the result. If the current variable value
is not a number it returns the empty string. N must be a number or a
discrete tag variable whose value is a number.

@item "-"(@i{N}) or SUB(@i{N})
@cindex Filter, "-"

Subtract N to variable and return the result. If the current variable value
is not a number it returns the empty string. N must be a number or a
discrete tag variable whose value is a number.

@item "*"(@i{N}) or MULT(@i{N})
@cindex Filter, "*"

Multiply N with variable and return the result. If the current variable value
is not a number it returns the empty string. N must be a number or a
discrete tag variable whose value is a number.

@item "/"(@i{N}) or DIV(@i{N})
@cindex Filter, "/"

Divide variable by N and return the result. If the current variable value
is not a number it returns the empty string. N must be a number or a
discrete tag variable whose value is a number.

@item ABS
@cindex Filter, ABS

Returns the absolute value.

@item ADD_PARAM(@i{NAME[=VALUE]})
@cindex Filter, ADD_PARAM

Add a parameter into an URL. This routine adds the '?' and '&'
character if needed. @i{VALUE} can be a tag variable name.

@item BR_2_EOL(@i{EOL})
@cindex Filter, BR_2_EOL

Replaces all occurrences of the @code{<br>} HTML tag by a line terminator
determined by EOL. EOL must be either CR (Carriage-Return), LF (Line-Feed),
LFCR (Line-Feed followed by Carriage-Return) or CRLF (Carriage-Return
followed by Line-Feed).

@item BR_2_LF
@cindex Filter, BR_2_LF

Shortcut for BR_2_EOL(LF).

@item CAPITALIZE
@cindex Filter, CAPITALIZE

Put all characters in the variable in lower case except characters after
a space or an underscore which are set in upper-case.

@item CLEAN_TEXT
@cindex Filter, CLEAN_TEXT

Keep only letters and digits all others characters are changed to
spaces.

@item COMA_2_POINT
@cindex Filter, COMA_2_POINT

Replaces all comas by points.

@item CONTRACT
@cindex Filter, CONTRACT

Converts any suite of spaces by a single space character.

@item DEL_PARAM(@i{NAME})
@cindex Filter, DEL_PARAM

Delete parameter NAME from the URL. This routine removes the '?' and '&'
character if needed. Returns the input string as-is if the parameter
is not found.

@item EXIST
@cindex Filter, EXIST

Returns @b{True} if variable is set and has a value different that the null
string and @b{False} otherwise.

@item FILE_EXISTS
@cindex Filter, FILE_EXISTS

Returns @b{True} if variable is set and has a value that corresponds
to a file name present on the file system and @b{False} otherwise.

@item FORMAT_DATE(@b{FORMAT})
@cindex Filter, FORMAT_DATE

Returns the date with the given format. The date must be in the ISO
format (YYYY-MM-DD) eventually followed by a space and the time with
the format HH:MM:SS. If the date is not given in the right format it
returns the date as-is. The format is using the GNU/date description
patterns as also implemented in @code{GNAT.Calendar.Time_IO}.

@itemize @bullet
@item @i{Characters}:

@itemize
@item @b{%}: a literal %
@item @b{n}: a newline
@item @b{t}: a horizontal tab
@end itemize

@item @i{Time fields}:

@itemize
@item @b{%H}: hour (00..23)
@item @b{%I}: hour (01..12)
@item @b{%k}: hour ( 0..23)
@item @b{%l}: hour ( 1..12)
@item @b{%M}: minute (00..59)
@item @b{%p}: locale's AM or PM
@item @b{%r}: time, 12-hour (hh:mm:ss [AP]M)
@item @b{%s}: seconds  since 1970-01-01  00:00:00 UTC (a nonstandard extension)
@item @b{%S}: second (00..59)
@item @b{%T}: time, 24-hour (hh:mm:ss)
@end itemize

@item @i{Date fields}:

@itemize
@item @b{%a}: locale's abbreviated weekday name (Sun..Sat)
@item @b{%A}: locale's full weekday name, variable length (Sunday..Saturday)
@item @b{%b}: locale's abbreviated month name (Jan..Dec)
@item @b{%B}: locale's full month name, variable length (January..December)
@item @b{%c}: locale's date and time (Sat Nov 04 12:02:33 EST 1989)
@item @b{%d}: day of month (01..31)
@item @b{%D}: date (mm/dd/yy)
@item @b{%h}: same as %b
@item @b{%j}: day of year (001..366)
@item @b{%m}: month (01..12)
@item @b{%U}: week number of year with  Sunday as first day of week (00..53)
@item @b{%w}: day of week (0..6) with 0 corresponding to Sunday
@item @b{%W}: week number of year with  Monday as first day of week (00..53)
@item @b{%x}: locale's date representation (mm/dd/yy)
@item @b{%y}: last two digits of year (00..99)
@item @b{%Y}: year with four digits (1970...)
@end itemize

@item @i{Padding}:

By default,  date pads numeric fields with zeroes. GNU date recognizes the following nonstandard numeric modifiers:
@itemize
@item @b{-} (hyphen): do not pad the field
@item @b{_} (underscore): pad the field with spaces
@end itemize
@end itemize

@item FORMAT_NUMBER([@i{DIGITSEP}])
@cindex Filter, FORMAT_NUMBER

Returns the number with a separator added between each 3 digits
blocks. The decimal part is not transformed. If the data is not a
number nothing is done. The default separator is a space, although you can
specify any separator (a single character) you wish. DIGITSEP can also be
the name of another tag, whose value (or the first character of it) will be
used as a separator.

@item IS_EMPTY
@cindex Filter, IS_EMPTY

Returns @b{True} if variable is the empty string and @b{False} otherwise.

@item LF_2_BR
@cindex Filter, LF_2_BR

Replaces all occurrences of the character LF (Line-Feed) by a
@code{<br>} HTML tag.

@item LOWER
@cindex Filter, LOWER

Put all characters in the variable in lower-case.

@item MATCH(@i{REGEXP})
@cindex Filter, MATCH

Returns @b{True} if variable match the regular expression passed as
filter's parameter. The regular expression is using a format as
found in @file{gawk}, @file{sed} or @file{grep} tools.

@item MAX(@i{N})
@cindex Filter, MAX

Returns the maximum value between the variable and the parameter.

@item MIN(@i{N})
@cindex Filter, MIN

Returns the minimum value between the variable and the parameter.

@item MOD(@i{N})
@cindex Filter, MOD

Returns variable modulo N. If the current variable value is not a
number it returns the empty string. N must be a number or a
discrete tag variable whose value is a number.

@item NEG
@cindex Filter, NEG

Change the sign of the value.

@item NO_DYNAMIC
@cindex Filter, NO_DYNAMIC

This is a special command filter which indicates that the tag must not
be searched in the dynamic tags. See @pxref{Lazy_Tag}. @code{NO_DYNAMIC} must
be the first filter. This filter returns the value as-is.

@item NO_DIGIT
@cindex Filter, NO_DIGIT

Replaces all digits by spaces.

@item NO_LETTER
@cindex Filter, NO_LETTER

Replaces all letters by spaces.

@item NO_SPACE
@cindex Filter, NO_SPACE

Removes all spaces in the variable.

@item OUI_NON
@cindex Filter, OUI_NON

If variable value is @b{True} it returns @b{Oui}, if @b{False} it
returns @b{Non}, otherwise does nothing. It keeps the way @b{True/False} is
capitalized (all upper, all lower or first letter capital).

@item POINT_2_COMA
@cindex Filter, POINT_2_COMA

Replaces all comas by points.

@item REPEAT(@i{N})
@cindex Filter, REPEAT

Returns @i{N} times the variable, @i{N} being passed as filter's parameter.
@i{N} must be a number or a discrete tag variable whose value is a number.

@item REPEAT(@i{STR})
@cindex Filter, REPEAT

This is the second @code{REPEAT} form. In this case @i{STR} is repeated
a number of time corresponding to the variable value which must be a number.

@item REPLACE(@i{REGEXP}[/@i{STR}])
@cindex Filter, REPLACE

This filter replaces @b{\n} (where @i{n} is a number) @i{STR}'s
occurrences by the corresponding match from @i{REGEXP}. The first match
in @i{REGEXP} will replace @b{\1}, the second match @b{\2} and so
on. Each match in @i{REGEXP} must be parenthesized. It replaces only
the first match. @i{STR} is an optional parameter, its default value
is @b{\1}. It is possible to space characters in @i{STR} to avoid
parsing confusions. This is required if you need to have @b{@@_} or
@b{_@@} or a parenthesis in @i{STR} for example. @i{STR} can be a tag
variable name. @i{STR} can contain the following escaped characters :
@b{\n} Carriage Return, @b{\r} Line Feed and @b{\t} for Horizontal
Tabulation.

@item REPLACE_ALL(@i{REGEXP}[/@i{STR}])
@cindex Filter, REPLACE_ALL

Idem as above but replaces all occurrences.

@item REPLACE_PARAM(@i{NAME[=VALUE]})
@cindex Filter, REPLACE_PARAM

This is filter is equivalent to
ADD_PARAM(@i{NAME[=VALUE]}):DEL_PARAM(@i{NAME}). @i{VALUE} can be a
tag variable name.

@item REVERSE
@cindex Filter, REVERSE

Reverse the string.

@item SIZE
@cindex Filter, SIZE

Returns the size (number of characters) of the string value.

@item SLICE(@i{x .. y})
@cindex Filter, SLICE

Returns the sub-string starting from position x and ending to position
y. Note that the string to slice always start from position 1.
If x or y are negative, they are counted from the end of the string, so
that 0 matches the last character of the string, -1 matches the character
just before,...

@item TRIM
@cindex Filter, TRIM

Removes leading and trailing spaces.

@item UPPER
@cindex Filter, UPPER

Put all characters in the variable in upper-case.

@item WEB_ENCODE
@cindex Filter, WEB_ENCODE

As WEB_ESCAPE and also encodes all non 7-bit characters and non
printable characters using @b{&#xxx;} HTML encoding.

@item WEB_ESCAPE
@cindex Filter, WEB_ESCAPE

Replaces characters '<', '>', '"' and '&' by corresponding HTML
sequences: &lt; &gt; &quot; and &amp;

@item WEB_NBSP
@cindex Filter, WEB_NBSP

Replaces all spaces by an HTML non breaking space.

@item WRAP(@i{N})
@cindex Filter, WRAP

Wraps lines having more N characters.

@item YES_NO
@cindex Filter, YES_NO

If variable value is @b{True} it returns @b{Yes}, if @b{False} it
returns @b{No}, otherwise does nothing. It keeps the way @b{True/False} is
capitalized (all upper, all lower or first letter capital).

@end table

@c ---------------------------------------------------------------------------
@node User defined filters
@subsection User defined filters
@c ---------------------------------------------------------------------------

@noindent
It is also possible to define a new filter by registering a callback
routine associated with the filter name.

You can define three kinds of filters: filters that take no argument, and are
therefore simply used as in @@_FILTER:TAG_@@, filters that take one
or more arguments, used as in @@_FILTER(param1,param2):TAG_@@, and filters
that are implemented as tagged objects, and take the same form as the filters
with arguments described above.

The latter form of filters (using tagged types) provides slightly more
flexibility, as you can store your own user data in the filter when it is
registered. Among other things, this makes it possible to share filters
between various applications, when the filter needs to access some
application-specific variable as well.

The templates parser will not try to interpret the parameters for you, and
will simply return the string representation of the list of parameters,
for instance @code{"param1,param2"} in the example above. This provides
enhanced flexibility, since you are free to use any parameter-separator
you want, and to interpret parameters as integer, strings, references to
other tags,@dots{}

The templates parser doesn't support tag substitution within the parameter
list, but this is trivial to implement in your own code. For instance,
if the user has used @@_FILTER(REFTAG):TAG_@@, you are free to either
take @code{REFTAG} as a constant string, or as a reference to another tag,
to be looked up in a translation table. You should of course properly
document the behavior of your filter.

Here is the templates parser API for defining your own custom filters:

@TPEXP{      @b{type} Filter_Context @b{is record}
      Translations : Translate_Set;
      Lazy_Tag     : Dynamic.Lazy_Tag_Access;
   @b{end record};

   @b{type} Callback @b{is access function}
     (Value      : @b{in} String;
      Parameters : @b{in} String;
      Context    : @b{in} Filter_Context) @b{return} String;
   @i{--  User's filter callback}

   @b{type} Callback_No_Param @b{is access function}
     (Value   : @b{in} String;
      Context : @b{in} Filter_Context) @b{return} String;
   @i{--  User's filter callback}

   @b{procedure} Register_Filter
     (Name    : @b{in} String;
      Handler : @b{in} Callback);
   @i{--  Register user's filter Name using the specified Handler}

   @b{procedure} Register_Filter
     (Name    : @b{in} String;
      Handler : @b{in} Callback_No_Param);
   @i{--  Register user's filter Name using the specified Handler}}

In the above calls, Value is the value of the tag on which the filter
applies. In the examples above, that would be the value of @code{TAG}
as looked up in the translation table. Context contains the the translation
table and the current lazy tag object you can use if you need to look
up other tags.

Here is a simple example of a custom filter, which can be used to
generate HTML forms. In such a form, it is common to have some @code{<input>}
tags that need a @code{selected='selected'} attribute if the toggle
button should be selected. This can be done without the use of a filter,
of course, using a simple @code{@@@@IF@@@@} statement, but that makes the
template less readable. The custom filter below behaves as such: it takes
one argument, and compares the value of the tag on which the filter is
applied to that argument. If they are equal, the string
@code{selected='selected'} will be substituted. As a special case, if the
argument to the filter starts with a @code{'@@'} character, the argument
is interpreted as the name of a tag to look up first.

@TPEXP{
   @b{function} Custom_Select_Filter
     (Value      : @b{in} String;
      Parameters : @b{in} String;
      Context    : @b{in} Filter_Context) @b{return} String @b{is}
   begin
      @b{if} Parameters /= "" @b{and then} Parameters (Parameters'First) = '@@' @b{then}
         @b{if} Get (Get (Context.Translations,
                      Parameters (Parameters'First + 1 .. Parameters'Last))) =
           Value
         @b{then}
            return "selected='selected'";
         @b{end if};

      @b{elsif} Value = Parameters @b{then}
         return "selected='selected'";
      @b{end if};

      @b{return} "";
   @b{end} Custom_Select_Filter;

   Register_Filter ("SELECTED", Custom_Select_Filter'Access);
}

and a template would look like:

@TPEXP{
   <option value="foo" @@_SELECTED(@@SELECTED_STATUS):STATUS_@@ />}

@c --------------------------------------------------------------------------
@node Attributes
@section Attributes
@c --------------------------------------------------------------------------

@noindent
In addition to filters, you can also apply attributes to composite tags.
Attributes are placed after the tag name and preceded with a simple quote.
@code{@@_SOME_VAR['ATTRIBUTE_NAME]_@@}. It is possible to use filters
and attributes together. In that case the attribute is first evaluated and
the result is passed-through the filters.

You cannot define your own attributes.

Current supported attributes are:

@table @code

@item V'length
@cindex Attribute, 'Length

Returns the number of item in the composite tag (can be applied only
to a composite tag having a single nested level - a vector).

@item V'Up_Level(n)
@cindex Attribute, 'Up_Level

Use index from the table command @b{n} level(s) upper so this attribute must
be used in a nested table command tag. @code{'Up_Level} is equivalent
to @code{'Up_Level(1)} (can be applied only to a composite tag having
a single nested level - a vector).

@item M'Line
@cindex Attribute, 'Line

Returns the number of line in the composite tag. This is identical to
'Length but can be applied only to a composite tag having two nested
level - a matrix).

@item M'Min_Column
@cindex Attribute, 'Min_Column

Returns the size of smallest composite tag in M composite tag. This attribute
can be applied only to a composite tag having two nested level - a matrix.

@item M'Max_Column
@cindex Attribute, 'Max_Column

Returns the size of largest composite tag in M composite tag. This attribute
can be applied only to a composite tag having two nested level - a matrix.

@end table

@noindent
For example:

@TPEXP{If VEC is set to "@i{<1 , 2>}" and MAT to "@i{<a, b, c> ; <2, 3, 5, 7>}" then:

@@_VEC'Length_@@              ->  2
@@_ADD(3):VEC'Length_@@       ->  5
@@_MAT'Line_@@                ->  2
@@_MAT'Min_Column_@@          ->  3
@@_MAT'Max_Column_@@          ->  4}

@c --------------------------------------------------------------------------
@node Predefined tags
@section Predefined tags
@c --------------------------------------------------------------------------

@noindent
There are some specific tags that can be used in any
templates. Here is an exhaustive list:

@table @code

@item NOW
@cindex @@_NOW_@@

Current date and time with format "YYYY-MM-DD HH:MM:SS".

@item YEAR
@cindex @@_YEAR_@@

Current year number using 4 digits.

@item MONTH
@cindex @@_MONTH_@@

Current month number using 2 digits.

@item DAY
@cindex @@_DAY_@@

Current day number using 2 digits.

@item HOUR
@cindex @@_HOUR_@@

Current hour using range 0 to 23 using 2 digits.

@item MINUTE
@cindex @@_MINUTE_@@

Current minute using 2 digits.

@item SECOND
@cindex @@_SECOND_@@

Current seconds using 2 digits.

@item MONTH_NAME
@cindex @@_MONTH_NAME_@@

Current full month name (January .. December).

@item DAY_NAME
@cindex @@_DAY_NAME_@@

Current full day name (Monday .. Sunday).

@end table

@c ----------------------------------------------------------------------------
@node Dynamic tags
@section Dynamic tags
@cindex Dynamic tags
@c ----------------------------------------------------------------------------

@noindent
Dynamic tags are associations that are not created when @code{Parse} is called,
but only later on when they are actually needed.

Dynamic tags are handled through abstract interfaces and give the
opportunity to create tags dynamically while the template is being parsed.

@menu
* Lazy_Tag::
* Cursor_Tag::
@end menu

@c ---------------------------------------------------------------------------
@node Lazy_Tag
@subsection Lazy_Tag
@cindex Lazy_Tag
@c ---------------------------------------------------------------------------

@noindent
The @code{Lazy_Tag} object can be used to dynamically handle tags. Such
object can be passed to the @code{Parse} routines. If a template's tag
is not found in the translation dictionary, the @code{Lazy_Tag}'s Value
callback method is called by the parser. The default callback method
does nothing, it is up to the user to define it. The callback
procedure is defined as follow:

@TPEXP{@b{procedure} Value
  (Lazy_Tag     : @b{access} Dynamic.Lazy_Tag;
   Var_Name     : @b{in}     String;
   Translations : @b{in out} Translate_Set) @b{is abstract};
@i{--  Value is called by the Parse routines below if a tag variable was not}
@i{--  found in the set of translations. This routine must then add the}
@i{--  association for variable Name. It is possible to add other}
@i{--  associations in the translation table but a check is done to see if}
@i{--  the variable Name as been set or not. The default implementation does}
@i{--  nothing.}}

@noindent
One common usage is to handle tag variables that can be shared by
many templates and are not always used (because a conditional is False for
example). If computing the corresponding value (or values for a ...)
is somewhat expensive it is better to delay building such tag at the
point it is needed. Using a @code{Lazy_Tag} object, it is possible to do
so. The @code{Value} procedure will be called if the tag value is
needed. At this point, one can just add the corresponding association
into the @code{Translate_Set}. Note that it is possible to add more
than one association. If the association for @code{Var_Name} is not
given, this tag has no value.

@code{Value} will be called only once per template and per tag. This is so
that if the value for the tag is expensive to compute, you only pay the
price once, and the value is then cached for the remaining of the template.
If the value should be recomputed every time, you should consider using
a @code{Cursor_Tag} instead (@pxref{Cursor_Tag}).

@c ---------------------------------------------------------------------------
@node Cursor_Tag
@subsection Cursor_Tag
@cindex Cursor_Tag
@c ---------------------------------------------------------------------------

@noindent
In some cases, data structure on the Ada side can be so complex that it is
difficult to map it into a variable tag. The @code{Cursor_Tag} object has
been designed to work around such problem. Using a @code{Cursor_Tag}
it is possible to create an iterator through a data structure without
mapping it into a variable tag. The data stays on the Ada side.
To create a @code{Cursor_Tag} it is necessary to implement the following
abstract routines:

@TPEXP{@b{function} Dimension
  (Cursor_Tag : @b{access} Dynamic.Cursor_Tag;
   Var_Name   : @b{in}     String) @b{return} Natural @b{is abstract};
@i{--  Must return the number of dimensions for the given variable name. For}
@i{--  a matrix this routine should return 2 for example.}

@b{type} Path @b{is array} (Positive @b{range} <>) @b{of} Natural;
@i{--  A Path gives the full position of a given element in the cursor tag}

@b{function} Length
  (Cursor_Tag : @b{access} Dynamic.Cursor_Tag;
   Var_Name   : @b{in}     String;
   Path       : @b{in}     Dynamic.Path) @b{return} Natural @b{is abstract};
@i{--  Must return the number of item for the given path. The first}
@i{--  dimension is given by the Path (1), for the second column the Path is}
@i{--  (1, 2). Note that each dimension can have a different length. For}
@i{--  example a Matrix is not necessary square.}

@b{function} Value
  (Cursor_Tag : @b{access} Dynamic.Cursor_Tag;
   Var_Name   : @b{in}     String;
   Path       : @b{in}     Dynamic.Path) @b{return} String @b{is abstract};
@i{--  Must return the value for the variable at the given Path. Note that}
@i{--  this routine will be called only for valid items as given by the}
@i{--  dimension and Length above.}}

@c ----------------------------------------------------------------------
@node Template statements
@chapter Template statements
@c ----------------------------------------------------------------------

@noindent
There are five different type statements. A tag statement is surrounded
by @code{@@@@}. The tag statements are:

@menu
* Comments::
* INCLUDE statement::
* IF statement::
* TABLE statement::
* SET statement::
* INLINE statement::
* MACRO statement::
@end menu

@c -----------------------------------------------------------------------
@node Comments
@section Comments
@cindex Command, comments
@cindex Command, @@@@--
@c -----------------------------------------------------------------------

@noindent
Every line starting with @b{@@@@--} are comments and are completely
ignored by the parser. The resulting page will have the exact same
format and number of lines with or without the comments.

@TPEXP{@@@@-- This template is used to display the client's data
@@@@-- It uses the following tags:
@@@@--
@@@@--    @@_CID_@@       Client ID
@@@@--    @@_ITEMS_V_@@   List of items (vector tag)

<P>Client @@_CID_@@

...}

@c -----------------------------------------------------------------------
@node INCLUDE statement
@section INCLUDE statement
@cindex Command, INCLUDE
@c -----------------------------------------------------------------------

@noindent
This statement is used to include another template file. This is useful if you
have the same header and/or footer in all your HTML pages. For example:

@TPEXP{@@@@INCLUDE@@@@ header.tmplt

<P>This is by Web page

@@@@INCLUDE@@@@ footer.tmplt}

@noindent
It is also possible to pass arguments to the include file. These parameters
are given after the include file name. It is possible to reference these
parameters into the included file with the special variable names
@code{@@_$<n>_@@}, where @i{n} is the include's parameter index (0 is
the include file name, 1 the first parameter and so on).

@TPEXP{@@@@INCLUDE@@@@ another.tmplt @@_VAR_@@ azerty}

@noindent
In file @file{another.tmplt}

@table @code
@item @@_$0_@@
is another.tmplt
@item @@_$1_@@
is the variable @@_VAR_@@
@item @@_$2_@@
is the string "azerty"
@end table

If an include variable references a non existing include parameter the
tag is kept as-is.

Note that it is possible to pass the include parameters using names,
a set of positional parameters can be pass first, so all following
include commands are identical:

@TPEXP{@@@@INCLUDE@@@@ another.tmplt one two three four "a text"
@@@@INCLUDE@@@@ another.tmplt (one, two, 3 => three, 4 => four, 5 => "a text")
@@@@INCLUDE@@@@ another.tmplt (one, 5 => "a text", 3 => three, 2 => two, 4 => four)}

@noindent
The file name can also be a tag. In this case the file loading is deferred at
the parsing time.

@noindent
For security reasons the filename can't be a full pathname. If a full
pathname is passed then the leading directory separator is removed.

@c -----------------------------------------------------------------------
@node IF statement
@section IF statement
@cindex Command, IF
@c -----------------------------------------------------------------------

@noindent
This is the conditional statement. The complete form is:

@TPEXP{@@@@IF@@@@ <expression1>
   part1
@@@@ELSIF@@@@ <expression2>
   part2
@@@@ELSE@@@@
   part3
@@@@END_IF@@@@}

@noindent
<expression> is TRUE if it evaluates to one of "TRUE", "T" or
"1" and FALSE otherwise. Note that the test is not case sensitive.

@noindent
The part1 one will be parsed if expression1 evaluate to TRUE, part2
will be parsed if expression2 evaluate to TRUE and the part3 will
be parse in any other case. The @code{ELSIF} and @code{ELSE} parts are
optional.

The expression here is composed of Boolean variables
and/or Boolean expression. Recognized operators are:

@cindex Command, IF expression
@table @code
@item A = B
Returns TRUE if A equal B

@item A /= B
Returns TRUE if A is not equal B

@item A > B
Returns TRUE if A greater than B. If A and B are numbers it returns the
the number comparison (5 > 003 = TRUE) otherwise it returns the string
comparison (``5'' > ``003'' = FALSE).

@item A >= B
Returns TRUE if A greater than or equal to B. See above for rule about numbers.

@item A < B
Returns TRUE if A lesser than B. See above for rule about numbers.

@item A <= B
Returns TRUE if A lesser than or equal to B. See above for rule about numbers.

@item A and B
Returns TRUE if A and B is TRUE and FALSE otherwise.

@item A or B
Returns TRUE if A or B is TRUE and FALSE otherwise.

@item A xor B
Returns TRUE if either A or B (but not both) is TRUE and FALSE otherwise.

@item A in B
Returns TRUE if A is found into the composite tag B and FALSE
otherwise. B must be a tag. If B contains a single value then this
expression is equivalent to (A = B).

@item not A
Returns TRUE if either A is FALSE and FALSE otherwise.
@end table

The default evaluation order is done from left to right, all operators
having the same precedence. To build an expression it is possible to
use parenthesis to change the evaluation order. A value with
spaces must be quoted as a string. So valid expressions could be:

@TPEXP{@@@@IF@@@@ (@@_VAR1_@@ > 3) or (@@_COND1_@@ and @@_COND2_@@)

@@@@IF@@@@ not (@@_VAR1_@@ > 3) or (@@_COND1_@@ and @@_COND2_@@)

@@@@IF@@@@ (@@_VAR1_@@ > 3) and not @@_COND1_@@

@@@@IF@@@@ @@_VAR1_@@ = "a value"}

@noindent
Note also that variables and values can be surrounded by quotes if needed.
Quotes are needed if a value contain spaces.

Let's see an example using an @code{IF} tag statement. With the following
template:

@include user.tmplt.texi

@noindent
The following program:

@include user1.adb.texi

@noindent
Will display:

@include user1.adb.res

@noindent
But the following program:

@include user2.adb.texi

@noindent
Will display:

@include user2.adb.res

@c -----------------------------------------------------------------------
@node TABLE statement
@section TABLE statement
@cindex Command, TABLE
@c -----------------------------------------------------------------------

@noindent
Table tags are useful to generate @code{HTML} tables for example.
Basically the code between the @code{@@@@TABLE@@@@} and
@code{@@@@END_TABLE@@@@} will be repeated as many times as the vector
tag has values. If many vector tags are specified in a table
statement, the code between the table will be repeated a number of
times equal to the maximum length of all vector tags in the
@code{TABLE} tag statement.

A @code{TABLE} tag statement is a kind of implicit iterator. This is a very
important concept to build HTML tables. Using a composite tag variable in
a @code{@@@@TABLE@@@@} tag statement it is possible to build very
complex Web pages.

Syntax:

@cindex Command, TERMINATE_SECTIONS
@cindex Command, REVERSE
@cindex Command, TERSE
@TPEXP{@@@@TABLE['REVERSE]['TERMINATE_SECTIONS]['TERSE]@@@@
      ...
   [@@@@BEGIN@@@@]
      ...
   [@@@@SECTION@@@@]
      ...
   [@@@@END@@@@]
      ...
@@@@END_TABLE@@@@}

@noindent
Let's have an example. With the following template:

@include table.tmplt.texi

@noindent
And the following program:

@include table.adb.texi

@noindent
The following output will be generated:

@include table.adb.res

@noindent
Note that we use vector tag variables here. A discrete variable tag in a table
will be replaced by the same (the only one) value for each row. A vector
tag outside a table will be displayed as a list of values, each value
being separated by a specified separator. The default is a comma and a
space ", ".

The complete prototype for the @code{Tag} Assoc function is:

@TPEXP{@b{function} Assoc (Variable  : @b{in} String;
                Value     : @b{in} Tag;
                Separator : @b{in} String    := Default_Separator)
                @b{return} Association;
@i{--  Build an Association (Variable = Value) to be added to Translate_Table.}
@i{--  This is a tag association. Separator will be used when outputting the}
@i{--  a flat representation of the Tag (outside a table statement).}}

@noindent
A table can contain many sections. The section to use will be selected
depending on the current line. For example, a table with two sections
will use different data on even and odd lines. This is useful when you
want to alternate the line background color for a better readability
when working on HTML pages.

@noindent
A table with sections can have attributes:

@table @code

@item REVERSE

The items will be displayed in the reverse order.

@item TERMINATE_SECTIONS

This ensure that the table output will end
with the last section. If the number of data in the vector variable tag
is not a multiple of the number of sections then the remaining section
will be complete with empty tag value.

@item TERSE

Empty lines won't be output. If the composite tag used into the table has
an empty value then the corresponding line won't be output. This is
especially important to avoid empty ending lines for table containing
vector of different size.

@end table

@include table_section.tmplt.texi

@noindent
And the following program:

@include table_section.adb.texi

@noindent
The following output will be generated:

@include table_section.adb.res

@noindent
It is important to note that it is possible to avoid code
duplication by using the @code{@@@@BEGIN@@@@} and @code{@@@@END@@@@}
block statements. In this case only the code inside the block is part
of the section, the code outside is common to all sections. Here is
an example to generate an HTML table with different colors for each line:

@noindent
The template file above can be written this way:
@include table_block.tmplt.texi

@noindent
Into a table construct there are some additional variable tags available:

@table @code
@item @@_UP_TABLE_LINE_@@
@cindex @@_UP_TABLE_LINE_@@

This tag will be replaced by the table line number of the upper table
statement. It will be set to 0 outside a table statement or inside a
single table statement.

@item @@_TABLE_LINE_@@
@cindex @@_TABLE_LINE_@@

This tag will be replaced by the current table line number. It will be
replaced by 0 outside a table statement.

@item @@_NUMBER_LINE_@@
@cindex @@_NUMBER_LINE_@@

This is the number of line displayed in the table. It will be replaced
by 0 outside a table statement.

@item @@_TABLE_LEVEL_@@
@cindex @@_TABLE_LEVEL_@@

This is the table level number. A table construct declared in a table
has a level value of 2.  It will be replaced by 0 outside a table statement.

@end table

@noindent
Let's have a look at a more complex example with mixed IF and TABLE
statements.

@noindent
Here is the template:

@include table_if.tmplt.texi

@noindent
And the following program:

@include table_if.adb.texi

@noindent
The following output will be generated:

@include table_if.adb.res

@noindent
Table tag statements can also be used with matrix tag or more nested
tag variables. In this case, for a tag variable with N nested levels,
the Nth closest enclosing @code{TABLE} tag statement will be used for
the corresponding index. If there are not enough indexes, the last
axis are just streamed as a single text value.

@noindent
Let's see what happens for a matrix tag:

@enumerate

@item Inside a table of level 2 (a TABLE statement inside a TABLE
statement).

@noindent
In this case the first @code{TABLE} iterates through the matrix lines.
First iteration will use the first matrix's vector, second
iteration will use the second matrix's vector and so on. And the second
@code{TABLE} will be used to iterate through the vector's values.

@item Inside a table of level 1.

@noindent
In this case the @code{TABLE} iterates through the matrix lines. First
iteration will use the first matrix's vector, second iteration will
use the second matrix's vector and so on. Each vector is then converted to
a string by concatenating all values using the specified separator
(see Assoc constructor for Tag or @code{Set_Separator} routine).

@item Outside a table statement.

@noindent
In this case the matrix is converted to a string. Each line represents
a vector converted to a string using the supplied separator (see point
2 above), and each vector is separated by an ASCII.LF character. The
separators to use for each level can be specified using @code{Set_Separator}.

@end enumerate

@noindent
Let's look at an example, with the following template:

@include matrix.tmplt.texi

@noindent
Using the program:

@include matrix.adb.texi

@noindent
We get the following result:

@include matrix.adb.res

@c ---------------------------------------------------------------------------
@node SET statement
@section SET statement
@cindex Command, SET
@c ---------------------------------------------------------------------------

@noindent
The @code{SET} command tag can be used to define a constant or an
alias for an include file parameter. This is especially important in
the context of reusable template files. For example, instead of having
many references to the @b{red} color in an HTML document, it is better to
define a constant @var{COLOR} with the value @b{red} and use @var{COLOR}
everywhere. It is then easier to change the color afterward.

@noindent
The first form, to define a simple constant that can be used as any
other variable in a template file, is:

@TPEXP{@@@@SET@@@@ <name> = <value>}

@noindent
The second form, to define an alias for a template file parameter, is:

@TPEXP{@@@@SET@@@@ <name> = $n [| <default_value>]}

@noindent
In this case <name> is an alias for the Nth include parameter. In this
form it is also possible to define a default value that would be used
if the Nth include parameter is not specified.

Some examples:

@TPEXP{@@@@SET@@@@ COLOR = red

@@@@SET@@@@ SIZE = $1

@@@@SET@@@@ COLOR = $4 | green}

@noindent
It is important to note that a variable is set global to a template
file. It means that constants set into an include file are visible
into the parent template. This is an important feature to be able to
have a "theme" like include template file for example.

@c ---------------------------------------------------------------------------
@node INLINE statement
@section INLINE statement
@cindex Command, INLINE
@c ---------------------------------------------------------------------------

@noindent
The @code{INLINE} statement can be used to better control the
result's layout. For example it is not possible to have the results of
a vector tag on the same line, also it is not possible to have a
conditional output in the middle of a line. The @code{INLINE} block
tag statement can be used to achieve that.

Elements in an inlined block are separated by a single space by
default. It is possible to specify any string as the separator. The
text layout on an @code{INLINE} block has no meaning (the lines are
trimmed on both side). As part of the inline command it is possible to
specify texts to output before and after the block.

@noindent
Syntax:

@TPEXP{@@@@INLINE[(<before>)(<separator>)(<after>)]@@@@
      ...
@@@@END_INLINE@@@@}

@noindent
There are three supported uses:

@table @code
@item @@@@INLINE@@@@

In this case there is no text before and after the block and the
separator is a single space.

@item @@@@INLINE(<separator>)@@@@

In this case there is no text before and after the block and the
separator is the string given as parameter @i{<separator>}.

@item @@@@INLINE(<before>)(<separator>)(<after>)@@@@

In this case all three values are explicitly given.
@end table

@noindent
@i{<before>}, @i{<separator>} and @i{<after>} may contain control characters:

@table @code
@item \n
To insert a new-line (CR+LF or LF depending on the Operation System)

@item \r
To insert a line-feed

@item \\
To insert a single backslash
@end table

@noindent
Let's look at an example, with the following template:

@include table_inline.tmplt.texi

@noindent
Using the program:

@include table_inline.adb.texi

@noindent
We get the following result:

@include table_inline.adb.res

@noindent
Another example with an @code{IF} tag statement:

@include if_inline.tmplt.texi

@noindent
Using the program:

@include if_inline.adb.texi

@noindent
We get the following result:

@include if_inline.adb.res

@c ---------------------------------------------------------------------------
@node MACRO statement
@section MACRO statement
@cindex Command, MACRO
@c ---------------------------------------------------------------------------

@noindent
The @code{MACRO} statement is used to defined macros that can be used
in other places in the template. The macro statement takes a single
parameter which is the name of the macro.

@noindent
Syntax:

@TPEXP{@@@@MACRO(NAME)@@@@
      ...
@@@@END_MACRO@@@@}

@noindent
The code inside the macro can be anything supported by the templates
engine. There is no restriction. The parameters inside the macro are
referenced as @@_$N_@@ (where N is a number and corresponds to the Nth
parameter passed to the macro). There is no maximum number of
parameters. A reference to a parameter that has no corresponding formal
parameter at the call point is ignored (the value will be the empty
string).

@noindent
For example:

@include macro.tmplt.texi

For using macros @pxref{Macros}.

@c ----------------------------------------------------------------------
@node Macros
@chapter Macros
@c ----------------------------------------------------------------------

@noindent
A macro usage is like a tag but with a set of parameters passed inside
parenthesis. Macros support all filters but attributes can't be
used. It is important to note that macros are expanded at the point of
their calls. This implementation maximizes speed but uses more memory
as the definition is not shared. If the code is large it may be better
to use an @@@@INCLUDE@@@@ as the code is not expanded.

@noindent
Syntax:

@TPEXP{
@code{@@_[[FILTER[(parameter)]:]MACRO_NAME([PARAM1][,N=>PARAMN])_@@}.
}

@noindent
A macro call can have positional parameters (like @code{PARAM1} above)
or named (where the name is a number corresponding to the actual
parameter position) parameters (like @code{PARAMN} above).

@noindent
With the following definition:

@include macro.tmplt.texi

@noindent
Using the program:

@include macro.adb.texi

@noindent
We get the following result:

@include macro.adb.res

@c ----------------------------------------------------------------------

@node Other services
@chapter Other services

@menu
* Tag utils::
* XML representation::
* Templates2Ada::
* Templatespp::
* Debug::
@end menu

@node Tag utils
@section Tag utils
@cindex Tag utils

@noindent
The child package @code{Utils}, @pxref{Templates_Parser.Utils}
contains a routine to encode a Tag variable into a string and the
inverse routine that build a Tag given it's string
representation. This is useful for example, in the context of AWS to
store a Tag into a session variable. See the AWS project.

@node XML representation
@section XML representation
@cindex XML

@noindent
The child package @code{XML}, @pxref{Templates_Parser.XML} contains
routines to save a @code{Translation_Set} into an XML document or to
create a @code{Translation_Set} by loading an XML document. The XML
document must conform to a specific @code{DTD} (see the Ada spec file).

@c --------------------------------------------------------------------------
@c --  Templates2Ada
@c --------------------------------------------------------------------------

@node Templates2Ada
@section Templates2Ada
@cindex templates2ada

@noindent
@code{templates2ada} is a tool that will generate a set of Ada
packages from a templates file. These Ada packages can then be used in
your application to avoid hard-coded strings, and help maintain the
templates and the code synchronized.

One of its goal is to ensure that you are only setting tags that actually
exist in the template (and thus prevent, as much as possibly, typos in the
name of tags); also, when combined with other tools, to help ensure that all
tags needed by the template are properly set.

Templates2ada also has special knowledge about HTTP constructs
and will generate Ada constants for the HTTP parameters you might receive in
return. Once more the goal is to help avoid typos in the Ada code.

For instance, we will consider a simple template file, found in a local
file @file{resources/block1.thtml}. This template contains the following simple
html code:

@TPEXP{
<form>
  <input name="PARAM1" value="@@_TAG1_@@" />
  <input name="PARAM2" value="@@_TAG2_@@" />
</form>}

When you run @file{templates2ada} (as described in the following subsection),
the following Ada package will be generated. Note that this is only the
default output of @file{templates2ada}, which can be fully tailored to your
needs.

@TPEXP
{@b{package} Templates.Block1 @b{is}
  pragma Style_Checks (Off);
  Template : constant string := "resources/block1.thtml";
  Tag1 : constant String := "TAG1";
  Tag2 : constant String := "TAG2";
  @b{package} Http @b{is}
    Param1 : constant String := "PARAM1";
    Param2 : constant String := "PARAM2";
  @b{end} Http;
@b{end} Templates.Block1;}

@code{templates2ada} knows about special constructs in the template file.
Such templates are generally associated with html pages. It is possible to
specify within the template itself what the url associated with the template
is, so that it provides a convenient link between the two. Likewise, you
can also define explicitly what the possible HTTP parameters are when loading
that page. This is mostly useful when those parameters do not correspond to
some form fields within the page itself. The syntax for these two is the
following:

@TPEXP{
@@--  HTTP_URL(the_url): any comment you want
@@--  HTTP_GET(param1_name): description of the parameter
@@--  HTTP_GET(param2_name): description of the parameter
}

and that results in the following constants in the generated Ada package:

@TPEXP{
@b{package} Templates.Block1 @b{is}
  URL : constant String := "the_url";
  @b{package} Http @b{is}
     Param1_Name : constant String := "param1_name";
     Param2_Name : constant String := "param2_name";
  @b{end} Http;
@b{end} Templates.Block1;}

The templates parser API lets you define your own custom filters. It is
often useful for those filters to take parameters, just like the predefined
filters do. However, it is also useful for these parameters to be able to
check the value of other tags. One convention for doing this is to start the
name of the parameter with "@". See for example the example in
@pxref{User defined filters}. As a reminder, the template would look like

@TPEXP{
   <option value="foo" @@_SELECTED(@@SELECTED_STATUS):STATUS_@@ />}

The @code{templates2ada} tool knows about this special convention, and would
generate the following Ada package from this example:

@TPEXP{
@b{package} Templates.Block1 @b{is}
   Selected_Status : @b{constant} String := "SELECTED_STATUS";
   Status : @b{constant} String := "STATUS";
@b{end} Templates.Block1;}

@c --------------------------------------------------------------------------
@c -- Templates2Ada -- Running templates2ada
@c --------------------------------------------------------------------------

@subsection Running templates2ada
@noindent
This tool parses all the template files found in a directory, and then
generate an output file from these, based on a template file
(a default example of which is provided as @file{templates.tads}). The
latter contains in fact two examples, depending on whether one Ada
package should be generated per template, or whether a single package
should be build. In the former case, if you are using the GNAT compiler,
you should run @code{gnatchop} on the resulting file. Here is an example
to run this tool for the example we described above.

@TPEXP
{$ rm -f src/templates/*.ads
$ templates2ada -d resources/ -o src/templates/generated -r
$ cd src/templates; gnatchop -w -q generated
$ rm -f src/templates/generated}

If, in you Ada code, you no longer use hard-coded strings but only the
constants found in the output packages, this will ensure that you are
not trying to set tags that are never used in the template.

The other check that impacts the quality of your code is to ensure that
all tags that are used by the templates are properly set. This cannot be
ensured by the compiler only, but using an external tool it is relatively
to do.

For instance, if you are using GNAT, we recommend the following additional
targets in your @file{Makefile}:

@TPEXP
{  unset_tags:
        gnat xref -u main.adb | fgrep templates-}

This checks for all unused entities in files called @file{templates-*},
which are the files generated by @file{templates2ada}.

@file{templates2ada} can be used in other situations as well. For instance,
one possible use is to generate, as output, a new template file that itself
contains a series of @code{@@@@SET@@@@} commands. This generated file can
then be @code{@@@@INCLUDE@@@@}d in your own templates. We have used it with
some success when implementation a web server: it is often the case that hyper
links refer to other pages in the same server. We have avoided hard-coding the
URLs and the names of their HTTP GET parameters, by fetching these names from
the generated file we were talking above.

The templates parser comes with an example file, called @file{all_urls.thtml},
which can be used with the @code{-t} switch to @code{templates2ada}, and will
generated a template file as output. You would use it as:

@TPEXP
{@@@@INCLUDE@@@@ all_urls.html
<a href="@@_URI_BLOCK1_@@?@@_HTTP_BLOCK1__PARAM1_@@=12" />}

@noindent
and this ensures the link is valid.

@file{templates2ada} supports a number of command line switches:

@itemize @bullet
@item -d <dir>

This switch specifies the directory in which the templates file are
searched for.

@item -o <file>

This switch specifies the output file name

@item -e <ext>

This file specifies the file name extension for template files. All
files in the directory that have this extension will be processed by
templates2ada.

@item -t <tmplt>

This file specifies the template file to be used for the output file.
The templates parser comes with an example for such a file, called
@file{templates.tads}, that you can adapt to your own needs.

@item -r

Sub directories of the one specified by @code{-d} will also be searched.

@item -v

Activate the verbose mode. This will output a warning when an http
parameter has a name made only of template parser tags, since no matching
entry can then be created for it in the output file.

@end itemize

@c ---------------------------------------------------------------------------
@c --  Templates2ada -- customizing
@c ---------------------------------------------------------------------------

@subsection Customizing templates2ada
@noindent

As was mentioned before, the output of templates2ada is a single file that
results from parsing a template file. An example of such a file is provided
in the templates2ada distribution, as @file{templates.tads}.

You are strongly encouraged to modify this file to adapt it to your needs,
and then use the @code{-t} switch to @file{templates2ada} to make use of your
modified file.

This file contains extensive comments on how to make use, and customize, it.
This documentation is not duplicated here

@c --------------------------------------------------------------------------
@c --  Templatespp
@c --------------------------------------------------------------------------

@node Templatespp
@section Templatespp
@cindex templatespp

@noindent
@code{templatespp} is a pre-processor based on the template parser. It is
generally used from scripts to process files and generate other files. One
of the possible uses, for instance, is to write the CSS (style-sheet) of a
web site as a template file (for instance @file{mycss.tcss}), and use
template parser structures in there. This is a good way to share colors for
instance, or to name constants, as is often done in Ada code.

Here is a small example of such a CSS:

@TPEXP{
@@@@SET@@@@ COLOR1=blue
@@@@SET@@@@ COLOR2=red
@@@@SET@@@@ LENGTH1=10

body @{background:@@_COLOR1_@@@}
div  @{background:@@_COLOR2_@@@}
ul.class @{background:@@_COLOR1_@@@}  /* same color as body */

ul   @{width:@@_ADD(3):LENGTH1_@@px@} /* ul 3 pixels wider than li */
li   @{width:@@_LENGTH1_@@px@}
}

Such a file would be processed with the following command line:

@TPEXP{
   templatespp -o mycss.css mycss.tcss
}

@c ---------------------------------------------------------------------------
@c --  Debug
@c ---------------------------------------------------------------------------

@node Debug
@section Debug
@cindex Debug

@noindent
A set of routines to help to debug the @code{Templates_Parser} engine,
@pxref{Templates_Parser.Debug}. For example, @code{Debug.Print_Tree}
will display, to the standard output, a representation of the internal
semantic tree for a template file.

@c ----------------------------------------------------------------------
@node Templates_Parser API Reference
@appendix Templates_Parser API Reference
@c ----------------------------------------------------------------------

@menu
Templates_Parser User's API

* Templates_Parser::
* Templates_Parser.Debug::
* Templates_Parser.Utils::
* Templates_Parser.XML::
@end menu

@page
@node Templates_Parser
@appendixsec Templates_Parser
@cindex Templates_Parser

@include templates_parser.ads.texi

@page
@node Templates_Parser.Debug
@appendixsec Templates_Parser.Debug
@cindex Templates_Parser.Debug

@include templates_parser-debug.ads.texi

@page
@node Templates_Parser.Utils
@appendixsec Templates_Parser.Utils
@cindex Templates_Parser.Utils

@include templates_parser-utils.ads.texi

@page
@node Templates_Parser.XML
@appendixsec Templates_Parser.XML
@cindex Templates_Parser.XML

@include templates_parser-xml.ads.texi

@c ----------------------------------------------------------------------

@node Index
@unnumbered Index

@printindex cp

@bye
