graphviz_intro.swinb

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:- use_rendering(graphviz).
:- include(example(graphviz_swish)).
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# Visualising terms and SLD trees with Graphviz
[Graphviz](http://www.graphviz.org/) is a collection of programs for visualising graphs. Here, we conveniently use it for visualising Prolog terms and SLD trees.

The code in the box above defines the two main predicates `term/2` and `sld/2`. The query `?-term(+Term, -Dot)`, where `Term` is bound to a Prolog term, will return a variable `Dot`, which defines a tree in Graphviz format. For example, the query `?-term([a,b,b,a], Dot)` produces the following Graphviz input:

	Dot = '
        digraph {
        node [shape=plaintext, fontname=Courier, fontsize=12]
        0 [label="[|]"];
        1 [label="a"];
        0 -&gt; 1;
        2 [label="[|]"];
        0 -&gt; 2;
        3 [label="b"];
        2 -&gt; 3;
        4 [label="[|]"];
        2 -&gt; 4;
        5 [label="b"];
        4 -&gt; 5;
        6 [label="[|]"];
        4 -&gt; 6;
        7 [label="a"];
        6 -&gt; 7;
        8 [label="[]"];
        6 -&gt; 8;
        }
    '

Adding `X = dot(Dot)` to the query then invokes the Graphviz renderer:
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term([a,b,b,a], _Dot), X = dot(_Dot).
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See [here](http://www.graphviz.org/pub/scm/graphviz2/doc/info/command.html) for more information about how to use Graphviz programs from the command line.

Similarly, the query `?-sld(Goal,Dot)`, where Goal is bound to a Prolog goal, will produce an atom, which defines a tree in Graphviz format. For example, the query `?-sld(student_of(S,peter),Dot)` produces the following tree when rendered with Graphviz:
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sld(student_of(S,peter), _Dot), X = dot(_Dot).
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Now, try the example queries `?-term2` and `?-sld2` that have been pre-defined in [`graphviz_swish.pl`](graphviz_swish.pl).
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term2(_Dot), X = dot(_Dot).
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sld2(_Dot), X = dot(_Dot).
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