misc fixes

internal/object/errors.go

@@ -18,3 +18,17 @@ func (e BinaryOpError) Error() string {
 func NewBinaryOpError(left, right Object, op string) BinaryOpError {
 	return BinaryOpError{left, right, op}
 }
+
+// DivisionByZeroError is an error returned when dividing by zero
+type DivisionByZeroError struct {
+	left Object
+}
+
+func (e DivisionByZeroError) Error() string {
+	return fmt.Sprintf("cannot divide %s by zero", e.left)
+}
+
+// NewDivisionByZeroError returns a new DivisionByZeroError
+func NewDivisionByZeroError(left Object) DivisionByZeroError {
+	return DivisionByZeroError{left}
+}

internal/object/int.go

@@ -65,6 +65,9 @@ func (i Integer) Mul(other Object) (Object, error) {
 func (i Integer) Div(other Object) (Object, error) {
 	switch obj := other.(type) {
 	case Integer:
+		if obj.Value == 0 {
+			return nil, NewDivisionByZeroError(i)
+		}
 		return Integer{i.Value / obj.Value}, nil
 	default:
 		return nil, NewBinaryOpError(i, other, "/")