diff --git a/MathPad/MPSumFunction.m b/MathPad/MPSumFunction.m
index 8c2c9e1..31d5e01 100644
--- a/MathPad/MPSumFunction.m
+++ b/MathPad/MPSumFunction.m
@@ -12,8 +12,15 @@
 #import "MPExpressionEvaluator.h"
 #import "MPEvaluationContext.h"
 
+#define ReturnIfNil(test) if(test == nil) return nil
+
 @implementation MPSumFunction
 
++ (NSString *)localizedFunctionName
+{
+    return NSLocalizedString(@"Sum", @"Name of Sum Function");
+}
+
 #pragma mark Creation Methods
 - (instancetype)init
 {
@@ -100,35 +107,42 @@
 }
 
 #pragma mark Evaluating Functions
-- (NSDecimalNumber *)evaluateWithError:(MPParseError *__autoreleasing *)error
+- (MPTerm *)parseWithError:(MPParseError *__autoreleasing *)error
 {
     MPExpressionEvaluator *startEvaluator = self.startExpression.evaluator;
-    NSDecimalNumber *start = [startEvaluator evaluateVariableDefinition:YES error:error];
-    if (!start) {
-        return nil;
-    }
-    NSDecimalNumber *target = [self.targetExpression evaluateWithError:error];
-    if (!target) {
-        return nil;
-    }
+    MPTerm *start = [startEvaluator parseExpectingVariable:YES
+                                                     error:error];
+    ReturnIfNil(start);
+
+    MPExpressionEvaluator *targetEvaluator = self.targetExpression.evaluator;
+    MPTerm *target = [targetEvaluator parseExpectingVariable:NO
+                                                       error:error];
+    ReturnIfNil(target);
+    
+    NSString *variable = startEvaluator.definedVariable.copy;
     
     [[MPEvaluationContext sharedContext] push];
-    
+    [[MPEvaluationContext sharedContext] defineVariable:variable withValue:[NSNull null]];
     MPExpressionEvaluator *sumEvaluator = self.sumExpression.evaluator;
-    NSDecimalNumber *value = [NSDecimalNumber zero];
-    for (NSDecimalNumber *iterator = start; [iterator compare:target] <= 0; iterator = [iterator decimalNumberByAdding:[[NSDecimalNumber alloc] initWithInteger:1]]) {
-        [[MPEvaluationContext sharedContext] bindValue:iterator toName:startEvaluator.definedVariable];
-        NSDecimalNumber *summand = [sumEvaluator evaluateWithError:error];
-        if (summand) {
-            value = [value decimalNumberByAdding:summand];
-        } else {
-            return nil;
-        }
-    }
-    
+    MPTerm *sum = [sumEvaluator parseExpectingVariable:NO
+                                                 error:error];
+    ReturnIfNil(sum);
     [[MPEvaluationContext sharedContext] pop];
     
-    return value;
+    return [[MPTerm alloc] initWithBlock:^NSDecimalNumber *{
+        [[MPEvaluationContext sharedContext] push];
+        NSDecimalNumber *value = [NSDecimalNumber zero];
+        NSDecimalNumber *startValue = [start evaluate];
+        NSDecimalNumber *targetValue = [target evaluate];
+        for (NSDecimalNumber *iterator = startValue;
+             [iterator compare:targetValue] <= 0 ;
+             iterator = [iterator decimalNumberByAdding:[[NSDecimalNumber alloc] initWithInteger:1]]) {
+            [[MPEvaluationContext sharedContext] defineVariable:variable withValue:iterator];
+            value = [value decimalNumberByAdding:[sum evaluate]];
+        }
+        [[MPEvaluationContext sharedContext] pop];
+        return value;
+    }];
 }
 
 #pragma mark Working With Functions