Added postfixNode type to represent a node in the postfix representation of the regex

postfixNode.go

@@ -0,0 +1,49 @@
+package main
+
+type NodeType int
+
+// This is a list of the possible node types
+const (
+	CHARACTER NodeType = iota
+
+	PIPE
+	CONCATENATE
+	KLEENE
+	QUESTION
+	PLUS
+)
+
+// This represents a node in the postfix representation of the expression
+type postfixNode struct {
+	nodetype NodeType
+	contents []rune // Contents of the node - the length of this would only be >1 if the node represents a character class
+}
+
+// Creates and returns a postfixNode based on the given contents
+func newPostfixNode(contents ...rune) postfixNode {
+	if len(contents) < 1 {
+		panic("Empty node.")
+	}
+	to_return := postfixNode{}
+	if len(contents) > 1 { // If the node has more than element, it must be a character class - the type must be CHARACTER
+		to_return.nodetype = CHARACTER
+		to_return.contents = contents
+	} else { // Node has one element, could be anything
+		switch contents[0] {
+		case '+':
+			to_return.nodetype = PLUS
+		case '?':
+			to_return.nodetype = QUESTION
+		case '*':
+			to_return.nodetype = KLEENE
+		case '|':
+			to_return.nodetype = PIPE
+		case CONCAT:
+			to_return.nodetype = CONCATENATE
+		default:
+			to_return.nodetype = CHARACTER
+		}
+		to_return.contents = append(to_return.contents, contents...)
+	}
+	return to_return
+}