diff --git a/parser/lexer.go b/parser/lexer.go
index b1a4a3e..2db36e9 100644
--- a/parser/lexer.go
+++ b/parser/lexer.go
@@ -8,6 +8,8 @@ import (
 
 // Run parses the source
 func (p *Parser) Run() error {
+	p.setDefaults()
+
 	p.pos.Reset()
 	return lexer.Run(p.lexStart)
 }
diff --git a/parser/parser.go b/parser/parser.go
index 723e589..739b657 100644
--- a/parser/parser.go
+++ b/parser/parser.go
@@ -12,6 +12,42 @@ type Parser struct {
 	src *lexer.Reader
 
 	pos lexer.Position
+
+	OnSection func(pos lexer.Position, name, subname string, hasSubname bool) error
+	OnField   func(pos lexer.Position, key, value string) error
+	OnComment func(pos lexer.Position, comment string) error
+	OnError   func(pos lexer.Position, content string, err error) error
+}
+
+func defaultOnSection(_ lexer.Position, _, _ string, _ bool) error { return nil }
+func defaultOnField(_ lexer.Position, _, _ string) error           { return nil }
+func defaultOnComment(_ lexer.Position, _ string) error            { return nil }
+
+func defaultOnError(pos lexer.Position, content string, err error) error {
+	return &lexer.Error{
+		Line:    pos.Line,
+		Column:  pos.Column,
+		Content: content,
+		Err:     err,
+	}
+}
+
+func (p *Parser) setDefaults() {
+	if p.OnSection == nil {
+		p.OnSection = defaultOnSection
+	}
+
+	if p.OnField == nil {
+		p.OnField = defaultOnField
+	}
+
+	if p.OnComment == nil {
+		p.OnComment = defaultOnComment
+	}
+
+	if p.OnError == nil {
+		p.OnError = defaultOnError
+	}
 }
 
 // NewParser creates a dosini-style parser using