Added eval operator

pkg/yqlib/operator_eval.go

@@ -0,0 +1,42 @@
+package yqlib
+
+import (
+	"container/list"
+)
+
+func evalOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	log.Debugf("Eval")
+	pathExpStrResults, err := d.GetMatchingNodes(context.ReadOnlyClone(), expressionNode.Rhs)
+	if err != nil {
+		return Context{}, err
+	}
+
+	expressions := make([]*ExpressionNode, pathExpStrResults.MatchingNodes.Len())
+	expIndex := 0
+	//parse every expression
+	for pathExpStrEntry := pathExpStrResults.MatchingNodes.Front(); pathExpStrEntry != nil; pathExpStrEntry = pathExpStrEntry.Next() {
+		expressionStrCandidate := pathExpStrEntry.Value.(*CandidateNode)
+
+		expressions[expIndex], err = ExpressionParser.ParseExpression(expressionStrCandidate.Node.Value)
+		if err != nil {
+			return Context{}, err
+		}
+
+		expIndex++
+	}
+
+	results := list.New()
+
+	for matchEl := context.MatchingNodes.Front(); matchEl != nil; matchEl = matchEl.Next() {
+		for expIndex = 0; expIndex < len(expressions); expIndex++ {
+			result, err := d.GetMatchingNodes(context, expressions[expIndex])
+			if err != nil {
+				return Context{}, err
+			}
+			results.PushBackList(result.MatchingNodes)
+		}
+	}
+
+	return context.ChildContext(results), nil
+
+}