Implement evaluation of method calls

--HG--
branch : dev

src/Orchard.Tests.Modules/SimpleScripting/EvaluatorTests.cs

@@ -1,4 +1,6 @@
-using System.Diagnostics;
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
 using NUnit.Framework;
 using Orchard.Widgets.SimpleScripting.Compiler;
 
@@ -33,11 +35,25 @@ namespace Orchard.Tests.Modules.SimpleScripting {
             Assert.That(result.Value, Is.EqualTo(4));
         }
 
+        [Test]
+        public void EvaluateSimpleMethodCall() {
+            var result = EvaluateSimpleExpression("print 1 + 2 * 3 - 6 / 2", 
+                (m, args) => (m == "print") ? (int)args[0] * 2 : 0);
+            Assert.That(result.IsError, Is.False);
+            Assert.That(result.Value, Is.EqualTo(4 * 2));
+        }
+
         private EvaluationResult EvaluateSimpleExpression(string expression) {
+            return EvaluateSimpleExpression(expression, (m, args) => null);
+        }
+
+        private EvaluationResult EvaluateSimpleExpression(
+            string expression, Func<string, IList<object>, object> methodInvocationCallback) {
+
             var ast = new Parser(expression).Parse();
             var result = new Interpreter().Evalutate(new EvaluationContext {
                 Tree = ast,
-                MethodInvocationCallback = (m, args) => null
+                MethodInvocationCallback = methodInvocationCallback
             });
             return result;
         }