var src = '(' + function () {

    var xs = [ 1, 2, [ 3, 4 ] ];

    var ys = [ 5, 6 ];

    somefunc([ xs, ys ]);

} + ')();\n';

src += 'var g = [ 5, 6 ];';

​

var output = falafel(src, 

    function (node) {

        if (node.type === 'ArrayExpression' && !node.inFunc) {

            node.update('fn(' + node.source() + ')');

        }

    },

    function (node) {

        if (node.type === 'FunctionExpression') {

            node.inFunc = true;

        }

        else if (node.parent && node.parent.inFunc) {

            //inherit from parent

            node.inFunc = node.parent.inFunc;

        }

        else { node.inFunc = false; }

    });

console.log(output.toString());