evaluationStage.go
func additionTypeCheck(left interface{}, right interface{}) bool {

	if isFloat64(left) && isFloat64(right) {
		return true
	}
	if !isString(left) && !isString(right) {
		return false
	}
	return true
}
func additionTypeCheck(left interface{}, right interface{}) bool {

	if isFloat64(left) && isFloat64(right) {
		return true
	}
	if !isString(left) && !isString(right) {
		return false
	}
	return true
}
/*
	Addition usually means between numbers, but can also mean string concat.
	String concat needs one (or both) of the sides to be a string.
*/