Provided by: libgraph-easy-perl_0.76-3_all 
NAME
Graph::Easy::Parser - Parse Graph::Easy from textual description
SYNOPSIS
# creating a graph from a textual description
use Graph::Easy::Parser;
my $parser = Graph::Easy::Parser->new();
my $graph = $parser->from_text(
'[ Bonn ] => [ Berlin ]'.
'[ Berlin ] => [ Rostock ]'.
);
print $graph->as_ascii();
print $parser->from_file('mygraph.txt')->as_ascii();
# Also works automatically on graphviz code:
print Graph::Easy::Parser->from_file('mygraph.dot')->as_ascii();
DESCRIPTION
"Graph::Easy::Parser" lets you parse simple textual descriptions of graphs, and constructs a
"Graph::Easy" object from them.
The resulting object can than be used to layout and output the graph.
Input
The input consists of text describing the graph, encoded in UTF-8.
Example:
[ Bonn ] --> [ Berlin ]
[ Frankfurt ] <=> [ Dresden ]
[ Bonn ] --> [ Frankfurt ]
[ Bonn ] = > [ Frankfurt ]
Graphviz
In addition there is a bit of magic that detects graphviz code, so input of the following form will also
work:
digraph Graph1 {
"Bonn" -> "Berlin"
}
Note that the magic detection only works for named graphs or graph with "digraph" at their start, so the
following will not be detected as graphviz code because it looks exactly like valid Graph::Easy code at
the start:
graph {
"Bonn" -> "Berlin"
}
See Graph::Easy::Parser::Graphviz for more information about parsing graphs in the DOT language.
VCG
In addition there is a bit of magic that detects VCG code, so input of the following form will also work:
graph: {
node: { title: Bonn; }
node: { title: Berlin; }
edge: { sourcename: Bonn; targetname: Berlin; }
}
See Graph::Easy::Parser::VCG for more information about parsing graphs in the VCG language.
Input Syntax
This is a very brief description of the syntax for the Graph::Easy language, for a full specification,
please see Graph::Easy::Manual.
nodes
Nodes are rendered (or "quoted", if you wish) with enclosing square brackets:
[ Single node ]
[ Node A ] --> [ Node B ]
Anonymous nodes do not have a name and cannot be referred to again:
[ ] -> [ Bonn ] -> [ ]
This creates three nodes, two of them anonymous.
edges
The edges between the nodes can have the following styles:
-> solid
=> double
.> dotted
~> wave
- > dashed
.-> dot-dash
..-> dot-dot-dash
= > double-dash
There are also the styles "bold", "wide" and "broad". Unlike the others, these can only be set via the
(optional) edge attributes:
[ AB ] --> { style: bold; } [ ABC ]
You can repeat each of the style-patterns as much as you like:
--->
==>
=>
~~~~~>
..-..-..->
Note that in patterns longer than one character, the entire pattern must be repeated e.g. all
characters of the pattern must be present. Thus:
..-..-..-> # valid dot-dot-dash
..-..-..> # invalid!
.-.-.-> # valid dot-dash
.-.-> # invalid!
In addition to the styles, the following two directions are possible:
-- edge without arrow heads
--> arrow at target node (end point)
<--> arrow on both the source and target node
(end and start point)
Of course you can combine all directions with all styles. However, note that edges without arrows
cannot use the shortcuts for styles:
--- # valid
.-.- # valid
.- # invalid!
- # invalid!
~ # invalid!
Just remember to use at least two repititions of the full pattern for arrow-less edges.
You can also give edges a label, either by inlining it into the style, or by setting it via the
attributes:
[ AB ] --> { style: bold; label: foo; } [ ABC ]
-- foo -->
... baz ...>
-- solid -->
== double ==>
.. dotted ..>
~~ wave ~~>
- dashed - >
= double-dash = >
.- dot-dash .->
..- dot-dot-dash ..->
Note that the two patterns on the left and right of the label must be the same, and that there is a
space between the left pattern and the label, as well as the label and the right pattern.
You may use inline label only with edges that have an arrow. Thus:
<-- label --> # valid
-- label --> # valid
-- label -- # invalid!
To use a label with an edge without arrow heads, use the attributes:
[ AB ] -- { label: edgelabel; } [ CD ]
groups
Round brackets are used to group nodes together:
( Cities:
[ Bonn ] -> [ Berlin ]
)
Anonymous groups do not have a name and cannot be referred to again:
( [ Bonn ] ) -> [ Berlin ]
This creates an anonymous group with the node "Bonn" in it, and links it to the node "Berlin".
Please see Graph::Easy::Manual for a full description of the syntax rules.
Output
The output will be a Graph::Easy object (unless overridden with "use_class()"), see the documentation for
Graph::Easy what you can do with it.
EXAMPLES
See Graph::Easy for an extensive list of examples.
METHODS
"Graph::Easy::Parser" supports the following methods:
new()
use Graph::Easy::Parser;
my $parser = Graph::Easy::Parser->new();
Creates a new parser object. The valid parameters are:
debug
fatal_errors
The first will enable debug output to STDERR:
my $parser = Graph::Easy::Parser->new( debug => 1 );
$parser->from_text('[A] -> [ B ]');
Setting "fatal_errors" to 0 will make parsing errors not die, but just set an error string, which can be
retrieved with error().
my $parser = Graph::Easy::Parser->new( fatal_errors => 0 );
$parser->from_text(' foo ' );
print $parser->error();
See also catch_messages() for how to catch errors and warnings.
reset()
$parser->reset();
Reset the status of the parser, clear errors etc. Automatically called when you call any of the
"from_XXX()" methods below.
use_class()
$parser->use_class('node', 'Graph::Easy::MyNode');
Override the class to be used to constructs objects while parsing. The first parameter can be one of the
following:
node
edge
graph
group
The second parameter should be a class that is a subclass of the appropriate base class:
package Graph::Easy::MyNode;
use base qw/Graph::Easy::Node/;
# override here methods for your node class
######################################################
# when overriding nodes, we also need ::Anon
package Graph::Easy::MyNode::Anon;
use base qw/Graph::Easy::MyNode/;
use base qw/Graph::Easy::Node::Anon/;
######################################################
# and :::Empty
package Graph::Easy::MyNode::Empty;
use base qw/Graph::Easy::MyNode/;
######################################################
package main;
use Graph::Easy::Parser;
use Graph::Easy;
use Graph::Easy::MyNode;
use Graph::Easy::MyNode::Anon;
use Graph::Easy::MyNode::Empty;
my $parser = Graph::Easy::Parser;
$parser->use_class('node', 'Graph::Easy::MyNode');
my $graph = $parser->from_text(...);
The object $graph will now contain nodes that are of your custom class instead of plain
"Graph::Easy::Node".
When overriding nodes, you also should provide subclasses for "Graph::Easy::Node::Anon" and
"Graph::Easy::Node::Empty", and make these subclasses of your custom node class as shown above. For
edges, groups and graphs, you need just one subclass.
from_text()
my $graph = $parser->from_text( $text );
Create a Graph::Easy object from the textual description in $text.
Returns undef for error, you can find out what the error was with error().
This method will reset any previous error, and thus the $parser object can be re-used to parse different
texts by just calling "from_text()" multiple times.
from_file()
my $graph = $parser->from_file( $filename );
my $graph = Graph::Easy::Parser->from_file( $filename );
Creates a Graph::Easy object from the textual description in the file $filename.
The second calling style will create a temporary "Graph::Easy::Parser" object, parse the file and return
the resulting "Graph::Easy" object.
Returns undef for error, you can find out what the error was with error() when using the first calling
style.
error()
my $error = $parser->error();
Returns the last error, or the empty string if no error occurred.
If you want to catch warnings from the parser, enable catching of warnings or errors:
$parser->catch_messages(1);
# Or individually:
# $parser->catch_warnings(1);
# $parser->catch_errors(1);
# something which warns or throws an error:
...
if ($parser->error())
{
my @errors = $parser->errors();
}
if ($parser->warning())
{
my @warnings = $parser->warnings();
}
See Graph::Easy::Base for more details on error/warning message capture.
parse_error()
$parser->parse_error( $msg_nr, @params);
Sets an error message from a message number and replaces embedded templates like "##param1##" with the
passed parameters.
_parse_attributes()
my $attributes = $parser->_parse_attributes( $txt, $class );
my ($att, $multiples) = $parser->_parse_attributes( $txt, $class );
Internal usage only. Takes a text like this:
attribute: value; attribute2 : value2;
and returns a hash with the attributes.
In list context, also returns the max count of multiple attributes, e.g. 3 when it encounters something
like "red|green|blue". When
EXPORT
Exports nothing.
SEE ALSO
Graph::Easy. Graph::Easy::Parser::Graphviz and Graph::Easy::Parser::VCG.
AUTHOR
Copyright (C) 2004 - 2007 by Tels <http://bloodgate.com>
See the LICENSE file for information.
perl v5.36.0 2022-11-20 Graph::Easy::Parser(3pm)