ast.NodeVisitor for Skulpt

ast_node_visitor.js

/* Just a silly little bit of example code */
var filename = '__main__.py';
var python_source = 'a, b = 0';
parse = Sk.parse(filename, python_source);
ast = Sk.astFromParse(parse.cst, filename, parse.flags);

/* Actually useful stuff, taken from 
   https://github.com/python-git/python/blob/master/Lib/ast.py#L219 */

var iter_fields = function(node) {
    /** Return a list of [fieldname, value] pairs for each field in "node._fields"
    that is present on *node*. Notice we skip every other field, since the odd
    elements are accessor functions. **/
    var fieldList = [];
    for (var i = 0; i < node._fields.length; i += 2) {
        var field = node._fields[i];
        if (field in node) {
            fieldList.push([field, node[field]]);
        }
    }
    return fieldList;
}

/* Constructor for generic NodeVisitor */
function NodeVisitor() {};

/** Visit a node. **/
NodeVisitor.prototype.visit = function(node) {
    var method_name = 'visit_' + node._astname;
    if (method_name in this) {
        return this[method_name](node);
    } else {
        return this.generic_visit(node);
    }
}

/** Called if no explicit visitor function exists for a node. **/
NodeVisitor.prototype.generic_visit = function(node) {
    var fieldList = iter_fields(node);
    for (var i = 0; i < fieldList.length; i += 1) {
        var field = fieldList[i][0], value = fieldList[i][1];
        if (Array === value.constructor) {
            for (var j = 0; j < value.length; j += 1) {
                var subvalue = value[j];
                if ("_astname" in subvalue) {
                    this.visit(subvalue);
                }
            }
        } else if ("_astname" in value) {
            this.visit(value);
        }
    }
}

/* Example of inheriting visitor */
function CodeAnalyzer() {
    NodeVisitor.apply(this, Array.prototype.slice.call(arguments));
};
CodeAnalyzer.prototype = new NodeVisitor();
CodeAnalyzer.prototype.visit_Num = function(node) {
    console.log(node.n.v);
};
var ca = new CodeAnalyzer();