*Hack book* de `Hoa\Graph`

Unfortunately, the documentation of this library has not
been written yet. However, the `README.md`

file may contain
enough information to help you. This document is an extract of the
`README.md`

file.

Sorry for this inconvenience. Be ensured we are working hard to fix
this.

This library allows to create and manipulate directed graphs, a common data structure. A directed graph is basically a set of vertices (aka nodes) and directed edges between vertices.

## Quick usage

As a quick overview, we propose to see how to create a simple directed graph in memory and dump the result as a DOT script in order to visualize it in SVG. The graph implementation will use the adjacency list structure. Thus:

```
// Create the graph instance.
// By default, loops are not allowed and we would like loops for this example,
// so we enable them.
$graph = new Hoa\Graph\AdjacencyList(Hoa\Graph::ALLOW_LOOP);
// Create 4 vertices (aka nodes).
$n1 = new Hoa\Graph\SimpleNode('n1');
$n2 = new Hoa\Graph\SimpleNode('n2');
$n3 = new Hoa\Graph\SimpleNode('n3');
$n4 = new Hoa\Graph\SimpleNode('n4');
// Create edges (aka links) between them.
$graph->addNode($n1);
$graph->addNode($n2, [$n1]); // n2 has parent n1.
$graph->addNode($n3, [$n1, $n2, $n3]); // n3 has parents n1, n2 and n3.
$graph->addNode($n4, [$n3]); // n4 has parent n3.
$graph->addNode($n2, [$n4]); // Add parent n4 to n2.
```

The directed graph is created in memory. Now, let's dump into the DOT language:

```
echo $graph;
/**
* Will output:
* digraph {
* n1;
* n2;
* n3;
* n4;
* n1 -> n2;
* n1 -> n3;
* n2 -> n3;
* n3 -> n3;
* n3 -> n4;
* n4 -> n2;
* }
*/
```

Then, to compile this DOT script into an SVG document, we will use
`dot(1)`

:

```
$ dot -Tsvg -oresult.svg <( echo 'digraph { … }'; )
```

And the result should look like the following image:

We can see that `n1`

is the parent of `n2`

and `n3`

. `n2`

is the parent of `n3`

.
`n3`

is parent of `n4`

and also or iself. And finally, `n4`

is the parent of
`n2`

.

Our directed graph is created. Depending of the node, we can add more
information on it. The `SimpleNode`

class has been used. It extends the
`Hoa\Graph\Node`

interface.

Une erreur ou une suggestion sur la documentation ? Les contributions sont ouvertes !