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+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+/* $Rev$ $Date$ */
+
+#ifndef tuscany_element_hpp
+#define tuscany_element_hpp
+
+/**
+ * Functions to help represent data as lists of elements and attributes.
+ */
+
+#include "list.hpp"
+#include "value.hpp"
+
+namespace tuscany
+{
+
+/**
+ * Tags used to tag lists of elements and attributes.
+ */
+const value attribute("attribute");
+const value element("element");
+const string atsign("@");
+
+/**
+ * Returns true if a value is an element.
+ */
+bool isElement(const value& v) {
+    if (!isList(v) || isNil(v) || element != car<value>(v))
+        return false;
+    return true;
+}
+
+/**
+ * Returns true if a value is an attribute.
+ */
+bool isAttribute(const value& v) {
+    if (!isList(v) || isNil(v) || attribute != car<value>(v))
+        return false;
+    return true;
+}
+
+/**
+ * Returns the name of an attribute.
+ */
+const value attributeName(const list<value>& l) {
+    return cadr(l);
+}
+
+/**
+ * Returns the value of an attribute.
+ */
+const value attributeValue(const list<value>& l) {
+    return caddr(l);
+}
+
+/**
+ * Returns the name of an element.
+ */
+const value elementName(const list<value>& l) {
+    return cadr(l);
+}
+
+/**
+ * Returns true if an element has children.
+ */
+const bool elementHasChildren(const list<value>& l) {
+    return !isNil(cddr(l));
+}
+
+/**
+ * Returns the children of an element.
+ */
+const list<value> elementChildren(const list<value>& l) {
+    return cddr(l);
+}
+
+/**
+ * Returns true if an element has a value.
+ */
+const bool elementHasValue(const list<value>& l) {
+    const list<value> r = reverse(l);
+    if (isSymbol(car(r)))
+        return false;
+    if(isList(car(r)) && !isNil((list<value>)car(r)) && isSymbol(car<value>(car(r))))
+        return false;
+    return true;
+}
+
+/**
+ * Returns the value of an element.
+ */
+const value elementValue(const list<value>& l) {
+    return car(reverse(l));
+}
+
+/**
+ * Convert an element to a value.
+ */
+const bool elementToValueIsList(const value& v) {
+    if (!isList(v))
+        return false;
+    const list<value> l = v;
+    return (isNil(l) || !isSymbol(car(l)));
+}
+
+const value elementToValue(const value& t) {
+    const list<value> elementsToValues(const list<value>& e);
+
+    // Convert an attribute
+    if (isTaggedList(t, attribute))
+        return mklist<value>(c_str(atsign + attributeName(t)), attributeValue(t));
+
+    // Convert an element
+    if (isTaggedList(t, element)) {
+
+        // Convert an element's value
+        if (elementHasValue(t)) {
+
+            // Convert a single value
+            if (!elementToValueIsList(elementValue(t)))
+                return mklist(elementName(t), elementValue(t));
+
+            // Convert a list value
+            return cons(elementName(t), mklist<value>(elementsToValues(elementValue(t))));
+        }
+
+        // Convert an element's children
+        return cons(elementName(t), elementsToValues(elementChildren(t)));
+    }
+
+    // Convert a value
+    if (!isList(t))
+        return t;
+    return elementsToValues(t);
+}
+
+/**
+ * Convert a list of elements to a list of values.
+ */
+const bool elementToValueIsSymbol(const value& v) {
+    if (!isList(v))
+        return false;
+    const list<value> l = v;
+    if (isNil(l))
+        return false;
+    if (!isSymbol(car(l)))
+        return false;
+    return true;
+}
+
+const list<value> elementToValueGroupValues(const value& v, const list<value>& l) {
+    if (isNil(l) || !elementToValueIsSymbol(v) || !elementToValueIsSymbol(car(l)))
+        return cons(v, l);
+    if (car<value>(car(l)) != car<value>(v))
+        return cons(v, l);
+    if (!elementToValueIsList(cadr<value>(car(l)))) {
+        const value g = mklist<value>(car<value>(v), mklist<value>(isList(cadr<value>(v))? (value)cdr<value>(v) : cadr<value>(v), isList(cadr<value>(car(l)))? (value)cdr<value>(car(l)) : cadr<value>(car(l))));
+        return elementToValueGroupValues(g, cdr(l));
+    }
+    const value g = mklist<value>(car<value>(v), cons<value>(isList(cadr<value>(v))? (value)cdr<value>(v) : cadr<value>(v), (list<value>)cadr<value>(car(l))));
+    return elementToValueGroupValues(g, cdr(l));
+
+}
+
+const list<value> elementsToValues(const list<value>& e) {
+    if (isNil(e))
+        return e;
+    return elementToValueGroupValues(elementToValue(car(e)), elementsToValues(cdr(e)));
+}
+
+/**
+ * Convert a value to an element.
+ */
+const value valueToElement(const value& t) {
+    const list<value> valuesToElements(const list<value>& l);
+
+    // Convert a name value pair
+    if (isList(t) && !isNil((list<value>)t) && isSymbol(car<value>(t))) {
+        const value n = car<value>(t);
+        const value v = isNil(cdr<value>(t))? value() : cadr<value>(t);
+
+        // Convert a single value to an attribute or an element
+        if (!isList(v)) {
+            if (substr(n, 0, 1) == atsign)
+                return mklist<value>(attribute, c_str(substr(n, 1)), v);
+            return mklist(element, n, v);
+        }
+
+        // Convert a list value
+        if (isNil((list<value>)v) || !isSymbol(car<value>(v)))
+            return cons(element, cons(n, mklist<value>(valuesToElements(v))));
+
+        // Convert a nested name value pair value
+        return cons(element, cons(n, valuesToElements(cdr<value>(t))));
+    }
+
+    // Convert a value
+    if (!isList(t))
+        return t;
+    return valuesToElements(t);
+}
+
+/**
+ * Convert a list of values to a list of elements.
+ */
+const list<value> valuesToElements(const list<value>& l) {
+    if (isNil(l))
+        return l;
+    return cons<value>(valueToElement(car(l)), valuesToElements(cdr(l)));
+}
+
+/**
+ * Returns a selector lambda function which can be used to filter
+ * elements against the given element pattern.
+ */
+struct selectorLambda {
+    const list<value> select;
+    selectorLambda(const list<value>& s) : select(s) {
+    }
+    const bool evalSelect(const list<value>& s, const list<value> v) const {
+        if (isNil(s))
+            return true;
+        if (isNil(v))
+            return false;
+        if (car(s) != car(v))
+            return false;
+        return evalSelect(cdr(s), cdr(v));
+    }
+    const bool operator()(const value& v) const {
+        if (!isList(v))
+            return false;
+        return evalSelect(select, v);
+    }
+};
+
+const lambda<bool(const value&)> selector(const list<value> s) {
+    return selectorLambda(s);
+}
+
+/**
+ * Returns the value of the attribute with the given name.
+ */
+struct filterAttribute {
+    const value name;
+    filterAttribute(const value& n) : name(n) {
+    }
+    const bool operator()(const value& v) const {
+        return isAttribute(v) && attributeName((list<value>)v) == name;
+    }
+};
+
+const value attributeValue(const value& name, const value& l) {
+    const list<value> f = filter<value>(filterAttribute(name), list<value>(l));
+    if (isNil(f))
+        return value();
+    return caddr<value>(car(f));
+}
+
+/**
+ * Returns child elements with the given name.
+ */
+struct filterElement {
+    const value name;
+    filterElement(const value& n) : name(n) {
+    }
+    const bool operator()(const value& v) const {
+        return isElement(v) && elementName((list<value>)v) == name;
+    }
+};
+
+const value elementChildren(const value& name, const value& l) {
+    return filter<value>(filterElement(name), list<value>(l));
+}
+
+/**
+ * Return the child element with the given name.
+ */
+const value elementChild(const value& name, const value& l) {
+    const list<value> f = elementChildren(name, l);
+    if (isNil(f))
+        return value();
+    return car(f);
+}
+
+}
+#endif /* tuscany_element_hpp */