1Parse::Template(3)    User Contributed Perl Documentation   Parse::Template(3)
2
3
4

NAME

6       Parse::Template - Processor for templates containing Perl expressions
7

SYNOPSIS

9         use Parse::Template;
10
11         my %template =
12           (
13            'TOP' =>  q!Text before %%$self->eval('DATA')%% text after!,
14            'DATA' => q!Insert data: ! .
15                      q!1. List: %%"@list$N"%%! .
16                      q!2. Hash: %%"$hash{'key'}$N"%%! .
17                      q!3. File content: %%<FH>%%! .
18                      q!4. Sub: %%&SUB()$N%%!
19           );
20
21         my $tmplt = new Parse::Template (%template);
22         open FH, "< foo";
23
24         $tmplt->env('var' => '(value!)');
25         $tmplt->env('list' => [1, 2, 10],
26                     'N' => "\n",
27                     'FH' => \*FH,
28                     'SUB' => sub { "->content generated by a sub<-" },
29                     'hash' => { 'key' => q!It\'s an hash value! });
30         print $tmplt->eval('TOP'), "\n";
31

DESCRIPTION

33       The "Parse::Template" class evaluates Perl expressions placed within a
34       text.  This class can be used as a code generator, or a generator of
35       documents in various document formats (HTML, XML, RTF, etc.).
36
37       The principle of template-based text generation is simple.  A template
38       consists of a text which includes expressions to be evaluated.
39       Interpretation of these expressions generates text fragments which are
40       substituted in place of the expressions.  In the case of
41       "Parse::Template" the expressions to be evaluated are Perl expressions
42       placed within two "%%".
43
44       Evaluation takes place within an environment in which, for example, you
45       can place data structures which will serve to generate the parts to be
46       completed.
47
48                    TEMPLATE
49                  Text + Perl Expression
50                       |
51                       +-----> Evaluation ----> Text(document or program)
52                       |
53                  Subs + Data structures
54                   ENVIRONMENT
55
56       The "Parse::Template" class permits decomposing a template into parts.
57       These parts are defined by a hash passed as an argument to the class
58       constructor: "Parse::Template-">"new('someKey', '... text with
59       expressions to evaluate ...')".  Within a part, a sub-part can be
60       included by means of an expression of the form:
61
62         $self->eval('SUB_PART_NAME')
63
64       $self designates the instance of the "Parse::Template" class.  In an
65       expression you can also use the $part which contains the part of the
66       template where the expression is found.
67
68       Within an expression it is possible to specify only the name of a part
69       to be inserted.  In this case a subroutine with the name of this part
70       is generated dynamically.  In the example given in the synopsis, the
71       insertion of the "TOP" part can thus be rewritten as follows:
72
73         'TOP' => q!Text before %%DATA()%% text after!
74
75       "DATA()" is placed within "%%" and is in effect treated as an
76       expression to be evaluated.
77
78       The subroutines take arguments.  In the following example, the argument
79       is used to control the depth of recursive calls of a template:
80
81         print Parse::Template->new(
82           'TOP' => q!%%$_[0] < 10 ? '[' . TOP($_[0] + 1) . ']' : ''%%!
83          )->eval('TOP', 0);
84
85       $_[0] initially contains 0. "TOP" is included as long as the argument
86       is less than 10.  For each inclusion, 1 is added to the argument.
87
88       The "env()" method permits constructing the environment required for
89       evaluation of a template.  Each entry to be defined within this
90       environment must be specified using a key consisting of the name of the
91       symbol to be created, associated with a reference whose type is that of
92       the entry to be created within this environment (for example, a
93       reference to an array to create an array).  A scalar variable is
94       defined by associating the name of the variable with its value.  A
95       scalar variable containing a reference is defined by writing
96       "'var'=">"\$variable", where $variable is a lexical variable that
97       contains the reference.
98
99       Each instance of "Parse::Template" is defined within a specific class,
100       a subclass of "Parse::Template".  The subclass contains the environment
101       specific to the template and inherits methods from the
102       "Parse::Template" class.
103
104       If a template is created from an existing template (i.e. calling "new"
105       as a method of the existing template), it inherits all the parts
106       defined by its ancestor.
107
108       In case of a syntax error in the evalutaion of an expression,
109       "Parse::Template" tries to indicate the template part and the
110       expression that is "incriminated".  If the variable
111       $Parse::Template::CONFESS contains the value TRUE, the stack of
112       evaluations is printed.
113

METHODS

115       new HASH
116           Constructor for the class. "HASH" is a hash which defines the
117           template text.
118
119           Example:
120
121             use Parse::Template;
122             $t = new Parse::Template('key' => 'associated text');
123
124       env HASH
125       env SYMBOL
126           Permits defining the environment that is specific to a template.
127
128           "env(SYMBOL)" returns the reference associated with the symbol, or
129           "undef" if the symbol is not defined.  The reference that is
130           returned is of the type indicated by the character ("&, $, %, @,
131           *") that prefixes the symbol.
132
133           Examples:
134
135             $tmplt->env('LIST' => [1, 2, 3])}   Defines a list
136
137             @{$tmplt->env('*LIST')}             Returns the list
138
139             @{$tmplt->env('@LIST')}             Ditto
140
141       eval PART_NAME
142           Evaluates the template part designated by "PART_NAME".  Returns the
143           string resulting from this evaluation.
144
145       getPart PART_NAME
146           Returns the designated part of the template.
147
148       ppregexp REGEXP
149           Preprocesses a regular expression so that it can be inserted into a
150           template where the regular expression delimiter is either a "/" or
151           a "!".
152
153       setPart PART_NAME => TEXT
154           "setPart()" permits defining a new entry in the hash that defines
155           the contents of the template.
156

EXAMPLES

158       The "Parse::Template" class can be used in all sorts of amusing ways.
159       Here are a few illustrations.
160
161   HTML Generator
162       The first example shows how to generate an HTML document by using a
163       data structure placed within the evaluation environment.  The template
164       consists of two parts, "DOC" and "SECTION".  The "SECTION" part is
165       called within the "DOC" part to generate as many sections as there are
166       elements in the array "section_content".
167
168         my %template = ('DOC' => <<'END_OF_DOC;', 'SECTION' => <<'END_OF_SECTION;');
169         <html>
170         <head></head>
171         <body>
172         %%
173         my $content;
174         for (my $i = 0; $i <= $#section_content; $i++) {
175           $content .= SECTION($i);
176         }
177         $content;
178         %%
179         </body>
180         </html>
181         END_OF_DOC;
182         %%
183         $section_content[$_[0]]->{Content} =~ s/^/<p>/mg;
184         join '', '<H1>', $section_content[$_[0]]->{Title}, '</H1>',
185                          $section_content[$_[0]]->{Content};
186         %%
187         END_OF_SECTION;
188
189         my $tmplt = new Parse::Template (%template);
190
191         $tmplt->env('section_content' => [
192             {
193               Title => 'First Section',
194               Content => 'Nothing to write'
195             },
196             {
197               Title => 'Second section',
198               Content => 'Nothing else to write'
199             }
200           ]
201         );
202
203         print $tmplt->eval('DOC'), "\n";
204
205   HTML generation using functional notation
206       The second example shows how to generate an HTML document using a
207       functional notation, in other words, obtaining the text:
208
209         <P><B>text in bold</B><I>text in italic</I></P>
210
211       from:
212
213         P(B("text in bold"), I("text in italic"))
214
215       The functions P(), B() and I() are defined as parts of a template.  The
216       Perl expression that permits producing the content of an element is
217       very simple, and reduces to:
218
219         join '', @_
220
221       The content to be evaluated is the same regardless of the tag and can
222       therefore be placed within a variable.  We therefore obtain the
223       following template:
224
225         my $ELT_CONTENT = q!%%join '', @_%%!;
226         my $HTML_T1 = new Parse::Template(
227              'DOC' => '%%P(B("text in bold"), I("text in italic"))%%',
228              'P'   => qq!<P>$ELT_CONTENT</P>!,
229              'B'   => qq!<B>$ELT_CONTENT</B>!,
230              'I'   => qq!<I>$ELT_CONTENT</I>!,
231             );
232         print $HTML_T1->eval('DOC'), "\n";
233
234       We can go further by making use of the $part variable, which is defined
235       by default in the environment of evaluation of the template:
236
237         my $ELT_CONTENT = q!%%"<$part>" . join('', @_) . "</$part>"%%!;
238         my $HTML_T2 = new Parse::Template(
239              'DOC' => '%%P(B("text in bold"), I("text in italic"))%%',
240              'P'   => qq!$ELT_CONTENT!,
241              'B'   => qq!$ELT_CONTENT!,
242              'I'   => qq!$ELT_CONTENT!,
243             );
244         print $HTML_T2->eval('DOC'), "\n";
245
246       Let's look at another step which automates the production of
247       expressions from the list of HTML tags which are of interest to us:
248
249         my $DOC = q!P(B("text in bold"), I("text in italic"))!;
250         my $ELT_CONTENT = q!%%"<$part>" . join('', @_) . "</$part>"%%!;
251         my $HTML_T3 = new Parse::Template(
252              'DOC' => qq!%%$DOC%%!,
253              map { $_ => $ELT_CONTENT } qw(P B I)
254             );
255         print $HTML_T3->eval('DOC'), "\n";
256
257       To benefit from the possibility of using the template parts as
258       procedures, we can inherit from the generated template class:
259
260         use Parse::Template;
261         my $ELT_CONTENT = q!%%"<$part>" . join('', @_) . "</$part>"%%!;
262         my $G = new Parse::Template(
263              map { $_ => $ELT_CONTENT } qw(H1 B I)
264             );
265         @main::ISA = ref($G);
266         *AUTOLOAD = \&Parse::Template::AUTOLOAD;
267         print H1(B("text in bold"), I("text in italic"));
268
269       The reference to "Parse::Template::AUTOLOAD" avoids the warning
270       message:
271
272         Use of inherited AUTOLOAD for non-method %s() is deprecated
273
274       Not very elegant.
275
276   HTML generation by method call
277       With a slight transformation it is possible to use a method-invocation
278       notation:
279
280         my $ELT_CONTENT = q!%%shift(@_); "<$part>" . join('', @_) . "</$part>"%%!;
281         my $HTML_T4 = new Parse::Template(
282              map { $_ => $ELT_CONTENT } qw(P B I)
283             );
284         print $HTML_T4->P(
285                           $HTML_T4->B("text in bold"),
286                           $HTML_T4->I("text in italic")
287                          ), "\n";
288
289       The "shift(@_)" permits getting rid of the template object, which we
290       don't need within the expression.
291
292   Inheritance of parts
293       In the following example the child template $C inherits the parts
294       defined in its parent template $A:
295
296         my %ancestor =
297           (
298            'TOP' => q!%%"Use the $part model and -> " . CHILD()%%!,
299            'ANCESTOR' => q!ANCESTOR %%"'$part' part\n"%%!,
300           );
301
302         my %child =
303           (
304            'CHILD' => q!CHILD %%"'$part' part"%% -> %%ANCESTOR() . "\n"%%!,
305           );
306         my $A = new Parse::Template (%ancestor);
307         my $C = $A->new(%child);
308         print $C->TOP();
309
310       The part <TOP> defined in $A can be called directly from $C, that
311       derives from $A.
312
313   Other examples
314       "Parse::Template" was initially created to serve as a code generator
315       for the "Parse::Lex" class.  You will find other examples of its use in
316       the classes "Parse::Lex", "Parse::CLex" and "Parse::Token".
317

NOTES CONCERNING THE CURRENT VERSION

319       I would be very interested to receive your comments and suggestions.
320

BUGS

322       Instances are not destroyed.  Therefore, do not use this class to
323       create a large number of instances.
324

AUTHOR

326       Philippe Verdret (with translation of documentation into English by
327       Ocrat)
328
330       Copyright (c) 1995-2001 Philippe Verdret. All rights reserved.  This
331       module is free software; you can redistribute it and/or modify it under
332       the same terms as Perl itself.
333
334
335
336perl v5.30.0                      2019-07-26                Parse::Template(3)
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