Fixed expressions to be able to do math with nested expressions.

__set.cpp

@@ -1,6 +1,6 @@
 #include "__set.h"
 #include "Exception.h"
-#include "Expression.h"
+#include "Operand.h"
 #include <iostream>
 
 namespace jet {
@@ -21,7 +21,7 @@ namespace jet {
 	 if(variableDefined("expr")) {
 	    if(variableDefined("eval"))
 	      throw coreutils::Exception("Cannot use eval with expr.");
-	    global.variables[variables["name"]] = Expression(variables["expr"]).string;	    
+	    global.variables[variables["name"]] = Operand(variables["expr"]).string;	    
 	 } else if(hasContainer) {
 	    processContainer(container);
 	    if(evaluate) {