diff --git a/char.go b/char.go
index 24dfd9a..4f588dd 100644
--- a/char.go
+++ b/char.go
@@ -3,7 +3,6 @@ package treerack
 type charParser struct {
 	name       string
 	id         int
-	commit     CommitType
 	not        bool
 	chars      []rune
 	ranges     [][]rune
@@ -12,14 +11,12 @@ type charParser struct {
 
 func newChar(
 	name string,
-	ct CommitType,
 	not bool,
 	chars []rune,
 	ranges [][]rune,
 ) *charParser {
 	return &charParser{
 		name:   name,
-		commit: ct,
 		not:    not,
 		chars:  chars,
 		ranges: ranges,
@@ -29,6 +26,7 @@ func newChar(
 func (p *charParser) nodeName() string { return p.name }
 func (p *charParser) nodeID() int      { return p.id }
 func (p *charParser) setID(id int)     { p.id = id }
+func (p *charParser) commitType() CommitType { return Alias }
 
 func (p *charParser) init(r *registry) error { return nil }
 
@@ -50,12 +48,8 @@ func (p *charParser) parser(r *registry, parsers *idSet) (parser, error) {
 	return p, nil
 }
 
-func (p *charParser) commitType() CommitType {
-	return p.commit
-}
-
-func (p *charParser) storeIncluded(*context, int, int) {
-	panic(cannotIncludeParsers(p.name))
+func (p *charParser) builder() builder {
+	return p
 }
 
 func (p *charParser) match(t rune) bool {
@@ -85,3 +79,18 @@ func (p *charParser) parse(t Trace, c *context) {
 		c.store.setMatch(c.offset, includedBy, c.offset+1)
 	}
 }
+
+func (p *charParser) build(c *context) ([]*Node, bool) {
+	t, ok := c.token()
+	if !ok {
+		panic("damaged parser context")
+	}
+
+	if !p.match(t) {
+		return nil, false
+	}
+
+	// always alias
+	c.offset++
+	return nil, true
+}
diff --git a/choice.go b/choice.go
index a0f9ce0..4377cf0 100644
--- a/choice.go
+++ b/choice.go
@@ -16,6 +16,12 @@ type choiceParser struct {
 	includedBy []int
 }
 
+type choiceBuilder struct {
+	name string
+	id int
+	commit CommitType
+}
+
 func newChoice(name string, ct CommitType, elements []string) *choiceDefinition {
 	return &choiceDefinition{
 		name:     name,
@@ -27,6 +33,7 @@ func newChoice(name string, ct CommitType, elements []string) *choiceDefinition
 func (d *choiceDefinition) nodeName() string { return d.name }
 func (d *choiceDefinition) nodeID() int      { return d.id }
 func (d *choiceDefinition) setID(id int)     { d.id = id }
+func (d *choiceDefinition) commitType() CommitType { return d.commit }
 
 func (d *choiceDefinition) init(r *registry) error {
 	parsers := &idSet{}
@@ -44,6 +51,10 @@ func (d *choiceDefinition) setIncludedBy(r *registry, includedBy int, parsers *i
 	return setItemsIncludedBy(r, d.elements, includedBy, parsers)
 }
 
+// TODO:
+// - it may be possible to initialize the parsers non-recursively
+// - maybe the whole definition, parser and builder can be united
+
 func (d *choiceDefinition) parser(r *registry, parsers *idSet) (parser, error) {
 	p, ok := r.parser(d.name)
 	if ok {
@@ -86,8 +97,8 @@ func (d *choiceDefinition) parser(r *registry, parsers *idSet) (parser, error) {
 	return cp, nil
 }
 
-func (d *choiceDefinition) commitType() CommitType {
-	return d.commit
+func (d *choiceDefinition) builder() builder {
+	return &choiceBuilder{}
 }
 
 func (p *choiceParser) nodeName() string { return p.name }
@@ -155,3 +166,10 @@ func (p *choiceParser) parse(t Trace, c *context) {
 	c.fail(from)
 	c.include(from, p.id)
 }
+
+func (b *choiceBuilder) nodeName() string { return b.name }
+func (b *choiceBuilder) nodeID() int      { return b.id }
+
+func (b *choiceBuilder) build(*context) ([]*Node, bool) {
+	return nil, false
+}
diff --git a/context.go b/context.go
index 150e7e7..10bdb3f 100644
--- a/context.go
+++ b/context.go
@@ -127,10 +127,10 @@ func (c *context) fail(offset int) {
 	c.match = false
 }
 
-func (c *context) finalize() error {
-	return ErrNotImplemented
-
-	if c.node.To < c.readOffset {
+func (c *context) finalize(root parser) error {
+	rootID := root.nodeID()
+	to, match, found := c.store.getMatch(0, rootID)
+	if !found || !match || to < c.readOffset {
 		return ErrUnexpectedCharacter
 	}
 
@@ -145,6 +145,8 @@ func (c *context) finalize() error {
 		}
 	}
 
+	return ErrNotImplemented
+
 	c.node.commit(c.tokens)
 	return nil
 }
diff --git a/parse.go b/parse.go
index d7d859d..e646a68 100644
--- a/parse.go
+++ b/parse.go
@@ -5,12 +5,12 @@ import "fmt"
 type definition interface {
 	nodeName() string
 	nodeID() int
+	commitType() CommitType
 	setID(int)
 	init(*registry) error
 	setIncludedBy(*registry, int, *idSet) error
 	parser(*registry, *idSet) (parser, error)
-	commitType() CommitType
-	// builder() builder
+	builder() builder
 }
 
 type parser interface {
@@ -22,7 +22,7 @@ type parser interface {
 type builder interface {
 	nodeName() string
 	nodeID() int
-	build(*context) *Node
+	build(*context) ([]*Node, bool)
 }
 
 func parserNotFound(name string) error {
@@ -83,7 +83,7 @@ func parse(t Trace, p parser, c *context) (*Node, error) {
 		return nil, ErrInvalidInput
 	}
 
-	if err := c.finalize(); err != nil {
+	if err := c.finalize(p); err != nil {
 		return nil, err
 	}
 
diff --git a/sequence.go b/sequence.go
index c30582a..4daf082 100644
--- a/sequence.go
+++ b/sequence.go
@@ -17,6 +17,12 @@ type sequenceParser struct {
 	includedBy []int
 }
 
+type sequenceBuilder struct {
+	name string
+	id int
+	commit CommitType
+}
+
 func newSequence(name string, ct CommitType, items []SequenceItem) *sequenceDefinition {
 	return &sequenceDefinition{
 		name:   name,
@@ -28,6 +34,7 @@ func newSequence(name string, ct CommitType, items []SequenceItem) *sequenceDefi
 func (d *sequenceDefinition) nodeName() string { return d.name }
 func (d *sequenceDefinition) nodeID() int      { return d.id }
 func (d *sequenceDefinition) setID(id int)     { d.id = id }
+func (d *sequenceDefinition) commitType() CommitType { return d.commit }
 
 func (d *sequenceDefinition) includeItems() bool {
 	return len(d.items) == 1 && d.items[0].Min == 1 && d.items[0].Max == 1
@@ -66,6 +73,7 @@ func (d *sequenceDefinition) setIncludedBy(r *registry, includedBy int, parsers
 }
 
 func (d *sequenceDefinition) parser(r *registry, parsers *idSet) (parser, error) {
+	// TODO: what is this for? test with sequence containing a sequence through a choice
 	if parsers.has(d.id) {
 		panic(cannotIncludeParsers(d.name))
 	}
@@ -124,8 +132,8 @@ func (d *sequenceDefinition) parser(r *registry, parsers *idSet) (parser, error)
 	return sp, nil
 }
 
-func (d *sequenceDefinition) commitType() CommitType {
-	return d.commit
+func (d *sequenceDefinition) builder() builder {
+	return &sequenceBuilder{}
 }
 
 func (p *sequenceParser) nodeName() string { return p.name }
@@ -189,3 +197,10 @@ func (p *sequenceParser) parse(t Trace, c *context) {
 	c.success(to)
 	c.include(from, p.id)
 }
+
+func (b *sequenceBuilder) nodeName() string { return b.name }
+func (b *sequenceBuilder) nodeID() int      { return b.id }
+
+func (b *sequenceBuilder) build(*context) ([]*Node, bool) {
+	return nil, false
+}
diff --git a/store.go b/store.go
index 515a324..dafeb67 100644
--- a/store.go
+++ b/store.go
@@ -58,6 +58,10 @@ func (s *store) ensureOffset(offset int) {
 }
 
 func (s *store) setMatch(offset, id, to int) {
+	if toe, match, ok := s.getMatch(offset, id); ok && match && toe == to {
+		return
+	}
+
 	s.ensureOffset(offset)
 	s.match[offset] = append(s.match[offset], id, to)
 }
diff --git a/syntax.go b/syntax.go
index 424b6b3..2e2d6d8 100644
--- a/syntax.go
+++ b/syntax.go
@@ -88,7 +88,7 @@ func childName(name string, childIndex int) string {
 
 func (s *Syntax) Class(name string, ct CommitType, not bool, chars []rune, ranges [][]rune) error {
 	cname := childName(name, 0)
-	if err := s.register(newChar(cname, Alias, not, chars, ranges)); err != nil {
+	if err := s.register(newChar(cname, not, chars, ranges)); err != nil {
 		return err
 	}
 
@@ -100,7 +100,7 @@ func (s *Syntax) CharSequence(name string, ct CommitType, chars []rune) error {
 	for i, ci := range chars {
 		ref := childName(name, i)
 		refs = append(refs, ref)
-		if err := s.register(newChar(ref, Alias, false, []rune{ci}, nil)); err != nil {
+		if err := s.register(newChar(ref, false, []rune{ci}, nil)); err != nil {
 			return err
 		}
 	}