BibTeX::Value(3pm)
NAME
Text::BibTeX::Value - interfaces to BibTeX values and simple values
SYNOPSIS
use Text::BibTeX;
$entry = new Text::BibTeX::Entry;
# set the 'preserve_values' flag to 1 for this parse
$entry->parse ($filename, $filehandle, 1);
# 'get' method now returns a Text::BibTeX::Value object
# rather than a string
$value = $entry->get ($field);
# query the `Value' object (list of SimpleValue objects)
@all_values = $value->values;
$first_value = $value->value (0);
$last_value = $value->value (-1);
# query the simple value objects -- type will be one of BTAST_STRING,
# BTAST_MACRO, or BTAST_NUMBER
use Text::BibTex (':nodetypes'); # import "node type" constants
$is_macro = ($first_value->type == BTAST_MACRO);
$text = $first_value->text;
DESCRIPTION
The "Text::BibTeX::Value" module provides two classes,
"Text::BibTeX::Value" and "Text::BibTeX::SimpleValue", which
respectively give you access to BibTeX "compound values" and "simple
values". Recall that every field value in a BibTeX entry is the
concatenation of one or more simple values, and that each of those
simple values may be a literal string, a macro (abbreviation), or a
number. Normally with "Text::BibTeX", field values are "fully
processed," so that you only have access to the string that results
from expanding macros, converting numbers to strings, concatenating all
sub-strings, and collapsing whitespace in the resulting string.
- For example, in the following entry:
- @article{homer97,
author = "Homer Simpson" # and # "Ned Flanders",
title = {Territorial Imperatives in Modern Suburbia},
journal = jss,
year = 1997 - }
- we see the full range of options. The "author" field consists of three
simple values: a string, a macro ("and"), and another string. The
"title" field is a single string, and the "journal" and "year" fields
are, respectively, a single macro and a single number. If you parse
this entry in the usual way:
$entry = new Text::BibTeX::Entry $entry_text;- then the "get" method on $entry would return simple strings. Assuming that the "and" macro is defined as " and ", then
$entry->get ('author')- would return the Perl string "Homer Simpson and Ned Flanders".
- However, you can also request that the library preserve the input
values in your entries, i.e. not lose the information about which
values use macros, which values are composed of multiple simple values, and so on. There are two ways to make this request: per-file and perentry. For a per-file request, use the "preserve_values" method on
your "File" object:
$bibfile = new Text::BibTeX::File $filename;
$bibfile->preserve_values (1);- $entry = new Text::BibTeX::Entry $bibfile;
$entry->get ($field); # returns a Value object - $bibfile->preserve_values (0);
$entry = new Text::BibTeX::Entry $bibfile;
$entry->get ($field); # returns a string - If you're not using a "File" object, or want to control things at a
finer scale, then you have to pass in the "preserve_values" flag when
invoking "read", "parse", or "parse_s" on your "Entry" objects:
# no File object, parsing from a string
$entry = new Text::BibTeX::Entry;
$entry->parse_s ($entry_text, 0); # preserve_values=0 (default)
$entry->get ($field); # returns a string- $entry->parse_s ($entry_text, 1);
$entry->get ($field); # returns a Value object - # using a File object, but want finer control
$entry->read ($bibfile, 0); # now get will return strings (default) $entry->read ($bibfile, 1); # now get will return Value objects - A compound value, usually just called a value, is simply a list of
simple values. The "Text::BibTeX::Value" class (hereinafter
abbreviated as "Value") provides a simple interface to this list; you
can request the whole list, or an individual member of the list. The
"SimpleValue" class gives you access to the innards of each simple
value, which consist of the type and the text. The type just tells you if this simple value is a string, macro, or number; it is represented
using the Perl translation of the "node type" enumeration from C. The possible types are "BTAST_STRING", "BTAST_NUMBER", and "BTAST_MACRO".
The text is just what appears in the original entry text, be it a
string, number, or macro. - For example, we could parse the above entry in "preserve values" mode
as follows:
$entry->parse_s ($entry_text, 1); # preserve_values is 1- Then, using the "get" method on $entry would return not a string, but a
"Value" object. We can get the list of all simple values using the
"values" method, or a single value using "value":
$author = $entry->get ('author'); # now a Text::BibTeX::Value object @all_values = $author->values; # array of Text::BibTeX::SimpleValue $second = $author->value (1); # same as $all_values[1]- The simple values may be queried using the "Text::BibTeX::SimpleValue" methods, "type" and "text":
$all_values[0]->type; # returns BTAST_STRING
$second->type; # returns BTAST_MACRO- $all_values[0]->text; # "Homer Simpson"
$second->text; # "and" (NOT the macro expansion!) - $entry->get ('year')->value (0)->text; # "1997"
METHODS
- Normally, you won't need to create "Value" or "SimpleValue"
objects---they'll be created for you when an entry is parsed, and
returned to you by the "get" method in the "Entry" class. Thus, the
query methods ("values" and "value" for the "Value" class, "type" and
"text" for "SimpleValue") are probably all you need to worry about. If you wish, though, you can create new values and simple values using the two classes' respective constructors. You can also put newly-created
"Value" objects back into an existing "Entry" object using the "set"
entry method; it doesn't matter how the entry was parsed, this is
acceptable anytime. - Text::BibTeX::Value methods
- new (SVAL, ...)
Creates a new "Value" object from a list of simple values. Each
simple value, SVAL, may be either a "SimpleValue" object or a
reference to a two-element list containing the type and text of the simple value. For example, one way to recreate the "author" field of the example entry in "DESCRIPTION" would be:
$and_macro = new Text::BibTeX::SimpleValue (BTAST_MACRO, 'and');
$value = new Text::BibTeX::Value([BTAST_STRING, 'Homer Simpson'],$and_macro,
[BTAST_STRING, 'Ned Flanders']);The resulting "Value" object could then be installed into an entry using the "set" method of the "Entry" class.values ()Returns the list of "SimpleValue" objects that make up a "Value"
object.value (NUM)Returns the NUM'th "SimpleValue" object from the list of
"SimpleValue" objects that make up a "Value" object. This is just like a Perl array reference: NUM is zero-based, and negative
numbers count from the end of the array. - Text::BibTeX::SimpleValue methods
- new (TYPE, TEXT)
Creates a new "SimpleValue" object with the specified TYPE and
TEXT. TYPE must be one of the allowed types for BibTeX simple
values, i.e. "BTAST_STRING", "BTAST_NUMBER", or "BTAST_MACRO".
You'll probably want to import these constants from "Text::BibTeX" using the "nodetypes" export tag:
use Text::BibTeX qw(:nodetypes);TEXT may be any string. Note that if TYPE is "BTAST_NUMBER" and
TEXT is not a string of digits, the "SimpleValue" object will be
created anyways, but a warning will be issued. No warning is
issued about non-existent macros. - type ()
Returns the type of a simple value. This will be one of the
allowed "node types" as described under "new" above. - text ()
Returns the text of a simple value. This is just the text that
appears in the original entry---unexpanded macro name, or
unconverted number. (Of course, converting numbers doesn't make
any difference from Perl; in fact, it's all the same in C too,
since the C code just keeps numbers as strings of digits. It's
simply a matter of whether the string of digits is represented as a string or a number, which you might be interested in knowing if you want to preserve the structure of the input as much possible.)
SEE ALSO
Text::BibTeX, Text::BibTeX::File, Text::BibTeX::Entry
AUTHOR
Greg Ward <gward@python.net>
COPYRIGHT
- Copyright (c) 1997-2000 by Gregory P. Ward. All rights reserved. This
file is part of the Text::BibTeX library. This library is free
software; you may redistribute it and/or modify it under the same terms as Perl itself.