User Contributed Perl Documentation lib::Text::Macros(3)
NAME
Text::Macros.pm - an object-oriented text macro engine
SYNOPSIS
use Text::Macros;
# poetic:
my $macro_expander = new Text::Macros qw( {{ }} );
$text = expand_macros $macro_expander $data_object, $text;
# noisy:
$macro_expander = Text::Macros->new( "\Q[[", "\Q]]", 1 );
print $macro_expander->expand_macros( $data_object, $text );
DESCRIPTION
Typical usage might look like this:
my $template = <<EOF;
To: [[ RecipientEmail ]]
From: [[ SenderEmail ]]
Subject: Payment Past Due on Account # [[ AccountNum ]]
Dear [[ RecipientName ]]:
Your payment of [[ PaymentAmount ]] is [[ DaysPastDue ]] days past due.
EOF
# get a data object from somewhere, e.g.:
my $data_object = $database->get_record_object( 'acctnum' => $account_num );
# make a macro expander:
my $macro_expander = Text::Macros->new( "\Q[[", "\Q]]" );
# expand the macros in the template:
my $email_text = $macro_expander->expand_macros( $data_object, $template );
To support this, a "data object" would need to exist which
would need to define methods which will be used as macro
names, e.g. like this:
package RecordObject;
sub RecipientEmail { $_[0]->{'RecipientEmail'} }
sub SenderEmail { $_[0]->{'SenderEmail'} }
sub AccountNum { $_[0]->{'AccountNum'} }
sub RecipientName { $_[0]->{'RecipientName'} }
sub PaymentAmount { $_[0]->{'PaymentAmount'} }
sub DaysPastDue { $_[0]->{'DaysPastDue'} }
Alternatively, the data object class might have AUTOLOAD
defined, for example like this:
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package RecordObject;
sub AUTOLOAD {
my $self = shift;
my $name = $AUTOLOAD;
$name =~ s/.*:://;
$self->{$name}
}
If this is the case, then the macro expander should be
instructed not to assert that the macro names encountered
are valid for the object -- since CAN might fail, even
though the calls will be handled by AUTOLOAD. To do this,
pass a true value for the third value to the constructor:
my $macro_expander = Text::Macros->new( "\Q[[", "\Q]]", 1 );
Macros can take arguments. Any strings which occur inside
the macro text after the macro name will be passed as
arguments to the macro method call. By default, the macro
name and any arguments are all separated by newlines. You
can override this behavior; see the documentation of
parse_args, below.
Example:
$macro_expander = new Macros qw( {{ }} );
print $macro_expander->expand_macros( $cgi_query,
"You entered {{ param
Name }} as your name."
);
This will replace the substring
{{ param
Name }}
with the result of calling
$cgi_query->param("Name")
(Obviously this example is a little contrived.)
METHODS
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The Constructor
Text::Macros->new( $open_delim, $close_delim, $no_CAN_check, $parse_args_cr );
The delimiters are regular expressions; this gives you the
greatest power in determining how macros are to be detected
in the text. But it means that if you simply want them to
be considered literal strings, then you must quotemeta them.
Since the macro expander will be calling object methods, you
have an option: do you want any encountered macro names to
be required to be valid for the given object? Or do you
have some kind of autoloading in effect, which will handle
undefined methods?
If you have some kind of autoloading, pass a true value for
the third argument to new(). If you want the expander to
assert CAN for each method, pass false (the default).
The fourth argument, $parse_args_cr, is a reference to a sub
which implements your macro argument parsing policy. See
the section on parse_args, below.
The Main Method: Expand Macros
$text = $macro_expander->expand_macros( $data_object, $text );
The $data_object argument is not an object of the Macros
package. Rather, this is the object upon which the macro
will be called as a method.
expand_macros() returns the result of replacing all the
macros it finds with their appropriate expansions. Note
that recursion can occur; that is, if the expansion of a
macro results in text which also contains a valid macro,
that new macro will also be expanded. The text will be
scanned for macros, and those macros will be expanded, until
none are found.
A Utility Method: Call Macro
$macro_expander->call_macro( $data_object, $macro_name, @arguments );
This is used internally by expand_macros(), but you can call
it directly if you wish.
Essentially all this does is this:
$macro_expander->call_macro( $data_object, $macro_name, @arguments );
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results in the call:
$data_object->$macro_name( @arguments );
All the macros supported by the data object can be
predefined, or you might have some kind of autoloading
mechanism in place for it. If you have autoloading in
effect, you should have passed a true value as the third
argument to new(). If you pass false (the default), the
call_macro() will check to see that the object CAN do the
method; and if it can't an exception will be thrown.
Note: data objects' macro methods must return a string.
They can take any number of arguments, which will all be
strings.
Parsing the Macro Arguments: parse_args
This is used internally by expand_macros().
expand_macros tries to call the sub which was passed by
reference as the fourth argument to new(), if there was one.
If no such coderef was given to the constructor, then
expand_macros calls the parse_args method in the
Text::Macros class, which implements the default behavior of
splitting the arg text on newlines, triming off
leading/trailing whitespace, and then dropping any list
elements which are '' (empty strings).
To implement some behavior other than the default, you may
derive a class from Text::Macros which overrides parse_args.
The parse_args method takes the Text::Macros object
reference as the first arg (as usual), and the macro text as
the second argument. This is all the text between the
delimiters, as it occurs in the template text. This method
is responsible for extracting the macro name and the values
of any arguments from the macro text. It is advisable that
the parse_args routine strip any leading and trailing
whitespace from the argument values. (It happens
automatically for the macro name, though, so you needn't
worry about that.)
Example:
package MyMacroParser;
@ISA = qw( Text::Macros );
sub parse_args {
my( $self, $macro_text ) = @;
# return a list of args extracted from $macrotext...
}
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And then, of course, you would instantiate a MyMacroParser
rather than a Text::Macros. Everything else about its usage
would be identical.
If you prefer, you can redefine the Text::Macros::parse_args
sub directly. That might look something like this:
*Text::Macros::parse_args = sub {
my( $self, $macro_text ) = @;
# return a list of args extracted from $macrotext...
};
Alternatively, you may pass a code reference as the fourth
argument to new(). The arguments to and results from this
sub are the same as for the parse_args method, as described
above, even though it is not (necessarily) a method itself.
The precedence is this: if a sub was passed to new(), that
is called; if not, the parse_args() of the derived class is
called, if defined; if not, the parse_args() of the base
class (Text::Macros) is called.
EXAMPLES
Brief examples of all these usage techniques can be found in
the test script, test.pl, which accompanies this
distribution. Any questions can be directed to the author
via email.
AUTHOR
jdporter@min.net (John Porter)
COPYRIGHT
This module is free software; you may redistribute it and/or
modify it under the same terms as Perl itself.
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