1 files changed, 33 insertions, 0 deletions
diff --git a/subex/arithmetic.go b/subex/arithmetic.go
index 7200ac7..5497a68 100644
--- a/subex/arithmetic.go
+++ b/subex/arithmetic.go
@@ -85,3 +85,36 @@ func multiplyValues(atoms []walk.Atom) ([]walk.Atom, error) {
 		return []walk.Atom{walk.ValueNumber(product)}, nil
 	}
 }
+
+// Does tries to cast all to numbers and negates them
+func negateValues(atoms []walk.Atom) ([]walk.Atom, error) {
+	var negatedNumbers []walk.Atom
+	values, err := walk.MemoryCompound(atoms)
+	if err != nil {
+		return nil, err
+	}
+	for _, value := range values {
+		switch v := value.(type) {
+			case walk.ValueNull:
+				negatedNumbers = append(negatedNumbers, walk.ValueNumber(0))
+			case walk.ValueBool:
+				if bool(v) {
+					negatedNumbers = append(negatedNumbers, walk.ValueNumber(-1))
+				} else {
+					negatedNumbers = append(negatedNumbers, walk.ValueNumber(0))
+				}
+			case walk.ValueNumber:
+				negatedNumbers = append(negatedNumbers, walk.ValueNumber(-v))
+			case walk.ValueString:
+				num, err := strconv.ParseFloat(string(v), 64)
+				if err == nil {
+					negatedNumbers = append(negatedNumbers, walk.ValueNumber(-num))
+				} else {
+					return nil, errors.New("Tried to sum non-castable string")
+				}
+			default:
+				return nil, errors.New("Tried to sum non-number")
+		}
+	}
+	return negatedNumbers, nil
+}