2 files changed, 36 insertions, 13 deletions

diff --git a/subex/main.go b/subex/main.go
index 593dbbd..2a5f5ad 100644
--- a/subex/main.go
+++ b/subex/main.go
@@ -118,7 +118,11 @@ func Main() {
 		return
 	}
 
-	valueOut := walk.MemoryCompound(output)
+	valueOut, error := walk.MemoryCompound(output)
+	if error != nil {
+		fmt.Println(error.Error())
+		return
+	}
 	for _, value := range valueOut {
 		fmt.Println(value)
 	}
diff --git a/subex/subexstate.go b/subex/subexstate.go
index 62e9d1a..855d44a 100644
--- a/subex/subexstate.go
+++ b/subex/subexstate.go
@@ -2,6 +2,8 @@ package subex
 
 import (
 	"main/walk"
+	"strconv"
+	"errors"
 )
 
 // A state of execution for the transducer
@@ -236,41 +238,54 @@ func (state SubexRangeState) accepting(store Store) [][]walk.Atom {
 	return nil
 }
 
-func sumValues(values []walk.Atom) walk.ValueNumber {
+func sumValues(atoms []walk.Atom) (walk.ValueNumber, error) {
 	var sum float64 = 0
+	values, err := walk.MemoryCompound(atoms)
+	if err != nil {
+		return 0, err
+	}
 	for _, value := range values {
 		switch v := value.(type) {
+			case walk.ValueNull:
 			case walk.ValueBool:
 				if (bool(v)) {
 					sum += 1
 				}
 			case walk.ValueNumber:
 				sum += float64(v)
-			case rune:
-				if '0' <= v && v <= '9' {
-					sum += float64(v - '0')
+			case walk.ValueString:
+				num, err := strconv.ParseFloat(string(v), 64)
+				if err == nil {
+					sum += num
+				} else {
+					return 0, errors.New("Tried to sum non-castable string")
 				}
 			default:
+				return 0, errors.New("Tried to sum non-number")
 		}
 	}
-	return walk.ValueNumber(sum)
+	return walk.ValueNumber(sum), nil
 }
 
 // Run the inputState machine and sum any values output, output the sum
-// Cast non numbers into numbers, ignore anything uncastable
+// Cast non numbers into numbers, branch dies if it is not castable
 type SubexSumState struct {
 	inputState SubexState
 	next SubexState
-	sum walk.ValueNumber
+	acc []walk.Atom
 }
 func (state SubexSumState) child() SubexState {
 	return state.inputState
 }
 func (state SubexSumState) nextAcc(output []walk.Atom) interface{} {
-	return sumValues(append(output, state.sum))
+	return walk.ConcatData(state.acc, output)
 }
 func (state SubexSumState) feedNext(acc interface{}, store Store, char walk.Atom) []SubexBranch {
-	total := acc.(walk.ValueNumber)
+	childOutput := acc.([]walk.Atom)
+	total, err := sumValues(childOutput)
+	if err != nil {
+		return nil
+	}
 	output := []walk.Atom{total}
 	nextStates := state.next.eat(store.clone(), char)
 	for i := range nextStates {
@@ -279,7 +294,11 @@ func (state SubexSumState) feedNext(acc interface{}, store Store, char walk.Atom
 	return nextStates
 }
 func (state SubexSumState) acceptNext(acc interface{}, store Store) [][]walk.Atom {
-	total := acc.(walk.ValueNumber)
+	childOutput := acc.([]walk.Atom)
+	total, err := sumValues(childOutput)
+	if err != nil {
+		return nil
+	}
 	output := []walk.Atom{total}
 	outputs := state.next.accepting(store.clone())
 	for i := range outputs {
@@ -288,11 +307,11 @@ func (state SubexSumState) acceptNext(acc interface{}, store Store) [][]walk.Ato
 	return outputs
 }
 func (state SubexSumState) nextParent(child SubexState, acc interface{}) SubexState {
-	sum := acc.(walk.ValueNumber)
+	childOutput := acc.([]walk.Atom)
 	return &SubexSumState {
 		inputState: child,
 		next: state.next,
-		sum: sum,
+		acc: childOutput,
 	}
 }
 func (state SubexSumState) eat(store Store, char walk.Atom) (nextStates []SubexBranch) {