I'm getting an error whilst trying to graph my PHP data

     <canvas id="cvs" width="600" height="250">[No canvas support]</canvas>
     <script>
        chart = new RGraph.Line({
            id: 'cvs',
            data: <?php print($data_string) ?>,
            options: {
                marginLeft: 35,
                marginRight: 5,
                marginInner: 10,
                tickmarksStyle: 'endcircle',
                xaxisLabels: <?php print($labels_string) ?>
            }
        }).draw()
    </script>

Uncaught SyntaxError: Unexpected token '<'
Error spec.: data: <?php print($data_string) ?>,

Well that error would seem to suggest that PHP isn't being parsed on your server.

Try viewing the source in your browser and if you see this:

data: <?php print($data_string) ?>

Then it would suggest that PHP isn't being parsed (because PHP should be replacing that on the server before the HTML is sent to your browser).

What you should be seeing is something like this:

data: [5,6,8,4,3,5,6],

Which is valid JavaScript.

thanks for the suggestion.
renamed extensone from html to .php now works fine.