Throw error instead of panicking

range2regex.go

@@ -99,17 +99,17 @@ func range2regex(start int, end int) (string, error) {
 	// Last range - tmp to rangeEnd
 	ranges = append(ranges, numRange{tmp, rangeEnd})
 
-	regex := "("
+	regex := string(NONCAPLPAREN_CHAR)
 	// Generate the regex
 	for i, rg := range ranges {
 		if i > 0 {
 			regex += "|"
 		}
-		regex += "("
+		regex += string(NONCAPLPAREN_CHAR)
 		startSlc := intToSlc(rg.start)
 		endSlc := intToSlc(rg.end)
 		if len(startSlc) != len(endSlc) {
-			panic("Ranges have unequal lengths.")
+			return "", fmt.Errorf("Error parsing numeric range")
 		}
 		for i := range startSlc {
 			if startSlc[i] == endSlc[i] {