Handle function returns

UpsilonTests/FunctionTests.cs

@@ -81,5 +81,75 @@ end
             Assert.NotNull(castType.Block);
         }
 
+        [Fact]
+        public void ReturnFromFunction()
+        {
+            const string input = @"
+function testFunc ()
+    return 5
+end
+a = testFunc()
+";
+            var script = new Script(input);
+            Assert.Empty(script.Diagnostics.Messages);
+            script.Evaluate();
+            Assert.Empty(script.Diagnostics.Messages);
+            Assert.True(script.Scope.TryGet("a", out var result));
+            Assert.Equal(5, (long)(NumberLong)result);
+        }
+
+        [Fact]
+        public void ReturnFromFunctionOnce()
+        {
+            const string input = @"
+function testFunc ()
+    return 5
+    return 10
+end
+a = testFunc()
+";
+            var script = new Script(input);
+            Assert.Empty(script.Diagnostics.Messages);
+            script.Evaluate();
+            Assert.Empty(script.Diagnostics.Messages);
+            Assert.True(script.Scope.TryGet("a", out var result));
+            Assert.Equal(5, (long)(NumberLong)result);
+        }
+
+        [Fact]
+        public void ReturnFromFunctionNested()
+        {
+            const string input = @"
+function testFunc ()
+    if true then
+        return 5
+    end
+    return 10
+end
+a = testFunc()
+";
+            var script = new Script(input);
+            Assert.Empty(script.Diagnostics.Messages);
+            script.Evaluate();
+            Assert.Empty(script.Diagnostics.Messages);
+            Assert.True(script.Scope.TryGet("a", out var result));
+            Assert.Equal(5, (long)(NumberLong)result);
+        }
+
+        [Fact]
+        public void ReturnFromScriptAsFunction()
+        {
+            const string input = @"
+a = 100
+return 60
+a = 87
+";
+            var script = new Script(input);
+            Assert.Empty(script.Diagnostics.Messages);
+            var result = script.Evaluate<NumberLong>();
+            Assert.Empty(script.Diagnostics.Messages);
+            Assert.Equal(60, (long)(NumberLong)result);
+        }
+
     }
 }