1 files changed, 18 insertions, 0 deletions
diff --git a/generate_error.go b/generate_error.go
index 7884151..8dfd964 100644
--- a/generate_error.go
+++ b/generate_error.go
@@ -14,3 +14,21 @@ type errAlreadyDeclared struct {
 func (e errAlreadyDeclared) Error() string {
 	return fmt.Sprintf("%d: redeclaration of %q\n", e.line, e.name)
 }
+
+type errUndeclared struct {
+	name string
+	line int
+}
+
+func (e errUndeclared) Error() string {
+	return fmt.Sprintf("%d: undeclared variable %q\n", e.line, e.name)
+}
+
+type errImmutable struct {
+	name string
+	line int
+}
+
+func (e errImmutable) Error() string {
+	return fmt.Sprintf("%d: cannot assign to constant %q\n", e.line, e.name)
+}