diff --git a/cmd/lambda/lambda.go b/cmd/lambda/lambda.go
index 4ac4180..76b2df3 100644
--- a/cmd/lambda/lambda.go
+++ b/cmd/lambda/lambda.go
@@ -8,8 +8,7 @@ import (
 	"git.maximhutz.com/max/lambda/internal/cli"
 	"git.maximhutz.com/max/lambda/internal/config"
 	"git.maximhutz.com/max/lambda/pkg/lambda"
-	"git.maximhutz.com/max/lambda/pkg/parser"
-	"git.maximhutz.com/max/lambda/pkg/tokenizer"
+	"git.maximhutz.com/max/lambda/pkg/saccharine"
 )
 
 // Run main application.
@@ -25,12 +24,12 @@ func main() {
 	cli.HandleError(err)
 
 	// Parse tokens.
-	tokens, err := tokenizer.GetTokens([]rune(input))
+	tokens, err := saccharine.GetTokens([]rune(input))
 	cli.HandleError(err)
 	logger.Info("Parsed tokens.", "tokens", tokens)
 
 	// Turn tokens into syntax tree.
-	expression, err := parser.GetTree(tokens)
+	expression, err := saccharine.GetTree(tokens)
 	cli.HandleError(err)
 	logger.Info("Parsed syntax tree.", "tree", lambda.Stringify(expression))
 
diff --git a/pkg/lambda/get_free_variables.go b/pkg/lambda/get_free_variables.go
index d729a84..3cb8b0e 100644
--- a/pkg/lambda/get_free_variables.go
+++ b/pkg/lambda/get_free_variables.go
@@ -12,7 +12,7 @@ func GetFreeVariables(e Expression) set.Set[string] {
 		return vars
 	case *Application:
 		vars := GetFreeVariables(e.Abstraction)
-		vars.Union(GetFreeVariables(e.Argument))
+		vars.Merge(GetFreeVariables(e.Argument))
 		return vars
 	default:
 		return nil
diff --git a/pkg/lambda/reduce.go b/pkg/lambda/reduce.go
index 95a5507..3a812d9 100644
--- a/pkg/lambda/reduce.go
+++ b/pkg/lambda/reduce.go
@@ -5,14 +5,13 @@ func ReduceOnce(e *Expression) bool {
 	case *Abstraction:
 		return ReduceOnce(&typed.Body)
 	case *Application:
-		fn, fnOk := typed.Abstraction.(*Abstraction)
-		if fnOk {
+		if fn, fnOk := typed.Abstraction.(*Abstraction); fnOk {
 			Substitute(&fn.Body, fn.Parameter, typed.Argument)
 			*e = fn.Body
 			return true
 		}
-		good := ReduceOnce(&typed.Abstraction)
-		if good {
+
+		if ReduceOnce(&typed.Abstraction) {
 			return true
 		}
 
diff --git a/pkg/lambda/substitute.go b/pkg/lambda/substitute.go
index 8d12145..ebc83c5 100644
--- a/pkg/lambda/substitute.go
+++ b/pkg/lambda/substitute.go
@@ -18,7 +18,7 @@ func Substitute(e *Expression, target string, replacement Expression) {
 		}
 
 		used := GetFreeVariables(typed.Body)
-		used.Union(replacementFreeVars)
+		used.Merge(replacementFreeVars)
 		freshVar := GenerateFreshName(used)
 		Rename(typed, typed.Parameter, freshVar)
 		Substitute(&typed.Body, target, replacement)
diff --git a/pkg/parser/parser.go b/pkg/parser/parser.go
deleted file mode 100644
index 81a6016..0000000
--- a/pkg/parser/parser.go
+++ /dev/null
@@ -1,98 +0,0 @@
-package parser
-
-import (
-	"fmt"
-
-	"git.maximhutz.com/max/lambda/pkg/iterator"
-	"git.maximhutz.com/max/lambda/pkg/lambda"
-	"git.maximhutz.com/max/lambda/pkg/tokenizer"
-)
-
-func ParseExpression(i *iterator.Iterator[tokenizer.Token]) (lambda.Expression, error) {
-	token, err := i.Pop()
-	if err != nil {
-		return nil, fmt.Errorf("could not get next token: %w", err)
-	}
-
-	switch token.Type {
-	case tokenizer.TokenVariable:
-		return lambda.NewVariable(token.Value), nil
-	case tokenizer.TokenDot:
-		return nil, fmt.Errorf("token '.' found without a corresponding slash (column %d)", token.Index)
-	case tokenizer.TokenSlash:
-		atoms := []string{}
-
-		for {
-			atom, atomErr := i.Pop()
-			if atomErr != nil {
-				return nil, fmt.Errorf("could not find parameter or terminator of function: %w", atomErr)
-			} else if atom.Type == tokenizer.TokenVariable {
-				atoms = append(atoms, atom.Value)
-			} else if atom.Type == tokenizer.TokenDot {
-				break
-			} else {
-				return nil, fmt.Errorf("expected function parameter or terminator, got '%v' (column %d)", atom.Value, atom.Index)
-			}
-		}
-
-		if len(atoms) == 0 {
-			return nil, fmt.Errorf("every function must have atleast one parameter (column %d)", token.Index)
-		}
-
-		body, bodyErr := ParseExpression(i)
-		if bodyErr != nil {
-			return nil, fmt.Errorf("could not parse function body: %w", bodyErr)
-		}
-
-		// Construction.
-		result := body
-		for i := len(atoms) - 1; i >= 0; i-- {
-			result = lambda.NewAbstraction(atoms[i], result)
-		}
-
-		return result, nil
-	case tokenizer.TokenOpenParen:
-		fn, fnErr := ParseExpression(i)
-		if fnErr != nil {
-			return nil, fmt.Errorf("could not parse call function: %w", fnErr)
-		}
-
-		args := []lambda.Expression{}
-
-		for {
-			if next, nextErr := i.Peek(); nextErr == nil && next.Type == tokenizer.TokenCloseParen {
-				break
-			}
-
-			arg, argErr := ParseExpression(i)
-			if argErr != nil {
-				return nil, fmt.Errorf("could not parse call argument: %w", argErr)
-			}
-
-			args = append(args, arg)
-		}
-
-		closing, closingErr := i.Pop()
-		if closingErr != nil {
-			return nil, fmt.Errorf("could not parse call terminating parenthesis: %w", closingErr)
-		} else if closing.Type != tokenizer.TokenCloseParen {
-			return nil, fmt.Errorf("expected call terminating parenthesis, got '%v' (column %v)", closing.Value, closing.Index)
-		}
-
-		// Construction.
-		result := fn
-		for _, arg := range args {
-			result = lambda.NewApplication(result, arg)
-		}
-
-		return result, nil
-	case tokenizer.TokenCloseParen:
-		return nil, fmt.Errorf("token ')' found without a corresponding openning parenthesis (column %d)", token.Index)
-	default:
-		return nil, fmt.Errorf("unknown token '%v' (column %d)", token.Value, token.Index)
-	}
-}
-
-func GetTree(tokens []tokenizer.Token) (lambda.Expression, error) {
-	return ParseExpression(iterator.New(tokens))
-}
diff --git a/pkg/saccharine/ast.go b/pkg/saccharine/ast.go
new file mode 100644
index 0000000..e0c4b05
--- /dev/null
+++ b/pkg/saccharine/ast.go
@@ -0,0 +1,41 @@
+package saccharine
+
+type Node interface {
+	IsNode()
+}
+
+/** ------------------------------------------------------------------------- */
+
+type Abstraction struct {
+	Parameters []string
+	Body       Node
+}
+
+type Application struct {
+	Abstraction Node
+	Arguments   []Node
+}
+
+type Variable struct {
+	Name string
+}
+
+/** ------------------------------------------------------------------------- */
+
+func NewAbstraction(parameter []string, body Node) *Abstraction {
+	return &Abstraction{Parameters: parameter, Body: body}
+}
+
+func NewApplication(abstraction Node, arguments []Node) *Application {
+	return &Application{Abstraction: abstraction, Arguments: arguments}
+}
+
+func NewVariable(name string) *Variable {
+	return &Variable{Name: name}
+}
+
+/** ------------------------------------------------------------------------- */
+
+func (_ Abstraction) IsNode() {}
+func (_ Application) IsNode() {}
+func (_ Variable) IsNode()    {}
diff --git a/pkg/saccharine/parser.go b/pkg/saccharine/parser.go
new file mode 100644
index 0000000..08aa5b5
--- /dev/null
+++ b/pkg/saccharine/parser.go
@@ -0,0 +1,80 @@
+package saccharine
+
+import (
+	"fmt"
+
+	"git.maximhutz.com/max/lambda/pkg/iterator"
+)
+
+func isVariableToken(t Token) bool {
+	return t.Type == TokenVariable
+}
+
+func ParseExpression(i *iterator.Iterator[Token]) (Node, error) {
+	token, err := i.Pop()
+	if err != nil {
+		return nil, fmt.Errorf("could not get next token: %w", err)
+	}
+
+	switch token.Type {
+	case TokenVariable:
+		return NewVariable(token.Value), nil
+	case TokenDot:
+		return nil, fmt.Errorf("token '.' found without a corresponding slash (column %d)", token.Index)
+	case TokenSlash:
+		tokens := i.PopWhile(isVariableToken)
+		variables := []string{}
+
+		for _, token := range tokens {
+			variables = append(variables, token.Value)
+		}
+
+		if dot, dotErr := i.Pop(); dotErr != nil {
+			return nil, fmt.Errorf("could not find parameter terminator: %w", dotErr)
+		} else if dot.Type != TokenDot {
+			return nil, fmt.Errorf("expected '.', got '%v' (column %d)", dot.Value, dot.Index)
+		}
+
+		body, bodyErr := ParseExpression(i)
+		if bodyErr != nil {
+			return nil, fmt.Errorf("could not parse function body: %w", bodyErr)
+		}
+
+		return NewAbstraction(variables, body), nil
+	case TokenOpenParen:
+		fn, fnErr := ParseExpression(i)
+		if fnErr != nil {
+			return nil, fmt.Errorf("could not parse call function: %w", fnErr)
+		}
+
+		args := []Node{}
+
+		for {
+			if next, nextErr := i.Peek(); nextErr == nil && next.Type == TokenCloseParen {
+				break
+			}
+
+			arg, argErr := ParseExpression(i)
+			if argErr != nil {
+				return nil, fmt.Errorf("could not parse call argument: %w", argErr)
+			}
+
+			args = append(args, arg)
+		}
+
+		closing, closingErr := i.Pop()
+		if closingErr != nil {
+			return nil, fmt.Errorf("could not parse call terminating parenthesis: %w", closingErr)
+		} else if closing.Type != TokenCloseParen {
+			return nil, fmt.Errorf("expected call terminating parenthesis, got '%v' (column %v)", closing.Value, closing.Index)
+		}
+
+		return NewApplication(fn, args), nil
+	}
+
+	return nil, fmt.Errorf("unexpected token '%v' (column %d)", token.Value, token.Index)
+}
+
+func GetTree(tokens []Token) (Node, error) {
+	return ParseExpression(iterator.New(tokens))
+}
diff --git a/pkg/tokenizer/token.go b/pkg/saccharine/token.go
similarity index 96%
rename from pkg/tokenizer/token.go
rename to pkg/saccharine/token.go
index 52a92d3..f21091c 100644
--- a/pkg/tokenizer/token.go
+++ b/pkg/saccharine/token.go
@@ -1,4 +1,4 @@
-package tokenizer
+package saccharine
 
 // All tokens in the pseudo-lambda language.
 type TokenType int
diff --git a/pkg/tokenizer/tokenizer.go b/pkg/saccharine/tokenizer.go
similarity index 99%
rename from pkg/tokenizer/tokenizer.go
rename to pkg/saccharine/tokenizer.go
index af2c946..598f5eb 100644
--- a/pkg/tokenizer/tokenizer.go
+++ b/pkg/saccharine/tokenizer.go
@@ -1,4 +1,4 @@
-package tokenizer
+package saccharine
 
 import (
 	"errors"
diff --git a/pkg/set/set.go b/pkg/set/set.go
index a55e1f3..dc4ac29 100644
--- a/pkg/set/set.go
+++ b/pkg/set/set.go
@@ -18,7 +18,7 @@ func (s *Set[T]) Remove(items ...T) {
 	}
 }
 
-func (s *Set[T]) Union(o Set[T]) {
+func (s *Set[T]) Merge(o Set[T]) {
 	for item := range o {
 		s.Add(item)
 	}