diff --git a/README.md b/README.md
index d636314..e79d420 100644
--- a/README.md
+++ b/README.md
@@ -157,6 +157,7 @@ This is what generates expressions from tokens.
 - [x] `<<=`, `>>=`
 - [x] `==`, `!=`, `<`, `<=`, `>`, `>=`
 - [x] `&&`, `||`
+- [ ] `!`, `-`
 
 ### Architecture
 
diff --git a/src/build/expression/Expression_test.go b/src/build/expression/Expression_test.go
index a313cf3..ebcc895 100644
--- a/src/build/expression/Expression_test.go
+++ b/src/build/expression/Expression_test.go
@@ -17,17 +17,22 @@ func TestParse(t *testing.T) {
 	}{
 		{"Identity", "1", "1"},
 		{"Basic calculation", "1+2", "(+ 1 2)"},
+
 		{"Same operator", "1+2+3", "(+ (+ 1 2) 3)"},
 		{"Same operator 2", "1+2+3+4", "(+ (+ (+ 1 2) 3) 4)"},
+
 		{"Different operator", "1+2-3", "(- (+ 1 2) 3)"},
 		{"Different operator 2", "1+2-3+4", "(+ (- (+ 1 2) 3) 4)"},
 		{"Different operator 3", "1+2-3+4-5", "(- (+ (- (+ 1 2) 3) 4) 5)"},
+
 		{"Grouped identity", "(1)", "1"},
 		{"Grouped identity 2", "((1))", "1"},
 		{"Grouped identity 3", "(((1)))", "1"},
+
 		{"Adding identity", "(1)+(2)", "(+ 1 2)"},
 		{"Adding identity 2", "(1)+(2)+(3)", "(+ (+ 1 2) 3)"},
 		{"Adding identity 3", "(1)+(2)+(3)+(4)", "(+ (+ (+ 1 2) 3) 4)"},
+
 		{"Grouping", "(1+2)", "(+ 1 2)"},
 		{"Grouping 2", "(1+2+3)", "(+ (+ 1 2) 3)"},
 		{"Grouping 3", "((1)+(2)+(3))", "(+ (+ 1 2) 3)"},
@@ -35,9 +40,11 @@ func TestParse(t *testing.T) {
 		{"Grouping right", "1*(2+3)", "(* 1 (+ 2 3))"},
 		{"Grouping same operator", "1+(2+3)", "(+ 1 (+ 2 3))"},
 		{"Grouping same operator 2", "1+(2+3)+(4+5)", "(+ (+ 1 (+ 2 3)) (+ 4 5))"},
+
 		{"Two groups", "(1+2)*(3+4)", "(* (+ 1 2) (+ 3 4))"},
 		{"Two groups 2", "(1+2-3)*(3+4-5)", "(* (- (+ 1 2) 3) (- (+ 3 4) 5))"},
 		{"Two groups 3", "(1+2)*(3+4-5)", "(* (+ 1 2) (- (+ 3 4) 5))"},
+
 		{"Operator priority", "1+2*3", "(+ 1 (* 2 3))"},
 		{"Operator priority 2", "1*2+3", "(+ (* 1 2) 3)"},
 		{"Operator priority 3", "1+2*3+4", "(+ (+ 1 (* 2 3)) 4)"},
@@ -46,10 +53,25 @@ func TestParse(t *testing.T) {
 		{"Operator priority 6", "1+2*3+4*5", "(+ (+ 1 (* 2 3)) (* 4 5))"},
 		{"Operator priority 7", "1+2*3*4*5*6", "(+ 1 (* (* (* (* 2 3) 4) 5) 6))"},
 		{"Operator priority 8", "1*2*3+4*5*6", "(+ (* (* 1 2) 3) (* (* 4 5) 6))"},
+
 		{"Complex", "(1+2-3*4)*(5+6-7*8)", "(* (- (+ 1 2) (* 3 4)) (- (+ 5 6) (* 7 8)))"},
 		{"Complex 2", "(1+2*3-4)*(5+6*7-8)", "(* (- (+ 1 (* 2 3)) 4) (- (+ 5 (* 6 7)) 8))"},
 		{"Complex 3", "(1+2*3-4)*(5+6*7-8)+9-10*11", "(- (+ (* (- (+ 1 (* 2 3)) 4) (- (+ 5 (* 6 7)) 8)) 9) (* 10 11))"},
-		{"Unary", "!", "!"},
+
+		{"Unary not", "!", "!"},
+		{"Unary not 2", "!a", "(! a)"},
+		{"Unary not 3", "!(!a)", "(! (! a))"},
+		{"Unary not 4", "!(a||b)", "(! (|| a b))"},
+		{"Unary not 5", "a || !b", "(|| a (! b))"},
+
+		{"Unary minus", "-", "-"},
+		{"Unary minus 2", "-a", "(- a)"},
+		{"Unary minus 3", "-(-a)", "(- (- a))"},
+		{"Unary minus 4", "-a+b", "(+ (- a) b)"},
+		{"Unary minus 5", "-(a+b)", "(- (+ a b))"},
+		{"Unary minus 6", "a + -b", "(+ a (- b))"},
+		{"Unary minus 7", "-a + -b", "(+ (- a) (- b))"},
+
 		{"Function calls", "a()", "(λ a)"},
 		{"Function calls 2", "a(1)", "(λ a 1)"},
 		{"Function calls 3", "a(1)+1", "(+ (λ a 1) 1)"},
@@ -77,8 +99,10 @@ func TestParse(t *testing.T) {
 		{"Function calls 25", "a(1-2*3)", "(λ a (- 1 (* 2 3)))"},
 		{"Function calls 26", "1+2*a()+4", "(+ (+ 1 (* 2 (λ a))) 4)"},
 		{"Function calls 27", "sum(a,b)*2+15*4", "(+ (* (λ sum a b) 2) (* 15 4))"},
+
 		{"Package function calls", "math.sum(a,b)", "(λ (. math sum) a b)"},
 		{"Package function calls 2", "generic.math.sum(a,b)", "(λ (. (. generic math) sum) a b)"},
+
 		{"Array access", "a[0]", "(@ a 0)"},
 		{"Array access 2", "a[b+c]", "(@ a (+ b c))"},
 		{"Array access 3", "a.b[c]", "(@ (. a b) c)"},
diff --git a/src/build/expression/Operator.go b/src/build/expression/Operator.go
index 1d9e18b..2a4ecdf 100644
--- a/src/build/expression/Operator.go
+++ b/src/build/expression/Operator.go
@@ -10,7 +10,7 @@ import (
 type Operator struct {
 	Symbol     string
 	Precedence int8
-	Operands   int
+	Operands   int8
 }
 
 // Operators defines the operators used in the language.
@@ -19,6 +19,7 @@ var Operators = map[token.Kind]*Operator{
 	token.Period: {".", 13, 2},
 	token.Call:   {"λ", 12, 1},
 	token.Array:  {"@", 12, 2},
+	token.Negate: {"-", 11, 1},
 	token.Not:    {"!", 11, 1},
 	token.Mul:    {"*", 10, 2},
 	token.Div:    {"/", 10, 2},
@@ -73,7 +74,7 @@ func numOperands(symbol token.Kind) int {
 		return -1
 	}
 
-	return operator.Operands
+	return int(operator.Operands)
 }
 
 func precedence(symbol token.Kind) int8 {
diff --git a/src/build/expression/Parse.go b/src/build/expression/Parse.go
index 7fbd6ad..22dbd39 100644
--- a/src/build/expression/Parse.go
+++ b/src/build/expression/Parse.go
@@ -117,7 +117,11 @@ func Parse(tokens []token.Token) *Expression {
 				newPrecedence := node.Precedence
 
 				if newPrecedence > oldPrecedence {
-					cursor.LastChild().Replace(node)
+					if len(cursor.Children) == numOperands(cursor.Token.Kind) {
+						cursor.LastChild().Replace(node)
+					} else {
+						cursor.AddChild(node)
+					}
 				} else {
 					start := cursor
 
diff --git a/src/build/token/Kind.go b/src/build/token/Kind.go
index 33df902..871e49f 100644
--- a/src/build/token/Kind.go
+++ b/src/build/token/Kind.go
@@ -38,10 +38,11 @@ const (
 	Shr                         // >>
 	LogicalAnd                  // &&
 	LogicalOr                   // ||
+	Not                         // ! (unary)
+	Negate                      // - (unary)
 	Equal                       // ==
 	Less                        // <
 	Greater                     // >
-	Not                         // !
 	NotEqual                    // !=
 	LessEqual                   // <=
 	GreaterEqual                // >=
diff --git a/src/build/token/Token.go b/src/build/token/Token.go
index 134f054..99cbe97 100644
--- a/src/build/token/Token.go
+++ b/src/build/token/Token.go
@@ -28,6 +28,11 @@ func (t Token) IsAssignment() bool {
 	return t.Kind > _assignments && t.Kind < _assignmentsEnd
 }
 
+// IsExpressionStart returns true if the token starts an expression.
+func (t Token) IsExpressionStart() bool {
+	return t.Kind == GroupStart || t.Kind == ArrayStart || t.Kind == BlockStart
+}
+
 // IsKeyword returns true if the token is a keyword.
 func (t Token) IsKeyword() bool {
 	return t.Kind > _keywords && t.Kind < _keywordsEnd
diff --git a/src/build/token/Tokenize.go b/src/build/token/Tokenize.go
index 610a36f..63ad4f7 100644
--- a/src/build/token/Tokenize.go
+++ b/src/build/token/Tokenize.go
@@ -26,8 +26,28 @@ func Tokenize(buffer []byte) List {
 			tokens = append(tokens, Token{Kind: ArrayEnd, Position: i, Length: 1})
 		case '\n':
 			tokens = append(tokens, Token{Kind: NewLine, Position: i, Length: 1})
+		case '-':
+			if len(tokens) == 0 || tokens[len(tokens)-1].IsOperator() || tokens[len(tokens)-1].IsExpressionStart() {
+				tokens = append(tokens, Token{Kind: Negate, Position: i, Length: 1})
+			} else {
+				if i+1 < Position(len(buffer)) && buffer[i+1] == '=' {
+					tokens = append(tokens, Token{Kind: SubAssign, Position: i, Length: 2})
+					i++
+				} else {
+					tokens = append(tokens, Token{Kind: Sub, Position: i, Length: 1})
+				}
+			}
+
 		case '/':
-			if i+1 >= Position(len(buffer)) || buffer[i+1] != '/' {
+			if i+1 < Position(len(buffer)) && buffer[i+1] == '/' {
+				position := i
+
+				for i < Position(len(buffer)) && buffer[i] != '\n' {
+					i++
+				}
+
+				tokens = append(tokens, Token{Kind: Comment, Position: position, Length: Length(i - position)})
+			} else {
 				position := i
 				i++
 
@@ -45,14 +65,6 @@ func Tokenize(buffer []byte) List {
 				}
 
 				tokens = append(tokens, Token{Kind: kind, Position: position, Length: Length(i - position)})
-			} else {
-				position := i
-
-				for i < Position(len(buffer)) && buffer[i] != '\n' {
-					i++
-				}
-
-				tokens = append(tokens, Token{Kind: Comment, Position: position, Length: Length(i - position)})
 			}
 
 			continue
diff --git a/src/build/token/Tokenize_test.go b/src/build/token/Tokenize_test.go
index 19f57e5..de67fbd 100644
--- a/src/build/token/Tokenize_test.go
+++ b/src/build/token/Tokenize_test.go
@@ -83,13 +83,81 @@ func TestNumber(t *testing.T) {
 }
 
 func TestOperator(t *testing.T) {
-	tokens := token.Tokenize([]byte(`+ - * /`))
+	tokens := token.Tokenize([]byte(`a + b - c * d / e`))
 
 	expected := []token.Kind{
+		token.Identifier,
 		token.Add,
+		token.Identifier,
 		token.Sub,
+		token.Identifier,
 		token.Mul,
+		token.Identifier,
 		token.Div,
+		token.Identifier,
+		token.EOF,
+	}
+
+	for i, kind := range expected {
+		assert.Equal(t, tokens[i].Kind, kind)
+	}
+}
+
+func TestNegateFirstToken(t *testing.T) {
+	tokens := token.Tokenize([]byte(`-a`))
+
+	expected := []token.Kind{
+		token.Negate,
+		token.Identifier,
+		token.EOF,
+	}
+
+	for i, kind := range expected {
+		assert.Equal(t, tokens[i].Kind, kind)
+	}
+}
+
+func TestNegateAfterGroupStart(t *testing.T) {
+	tokens := token.Tokenize([]byte(`(-a)`))
+
+	expected := []token.Kind{
+		token.GroupStart,
+		token.Negate,
+		token.Identifier,
+		token.GroupEnd,
+		token.EOF,
+	}
+
+	for i, kind := range expected {
+		assert.Equal(t, tokens[i].Kind, kind)
+	}
+}
+
+func TestNegateSub(t *testing.T) {
+	tokens := token.Tokenize([]byte(`-a-b`))
+
+	expected := []token.Kind{
+		token.Negate,
+		token.Identifier,
+		token.Sub,
+		token.Identifier,
+		token.EOF,
+	}
+
+	for i, kind := range expected {
+		assert.Equal(t, tokens[i].Kind, kind)
+	}
+}
+
+func TestNegateAfterOperator(t *testing.T) {
+	tokens := token.Tokenize([]byte(`-a + -b`))
+
+	expected := []token.Kind{
+		token.Negate,
+		token.Identifier,
+		token.Add,
+		token.Negate,
+		token.Identifier,
 		token.EOF,
 	}
 
@@ -99,18 +167,28 @@ func TestOperator(t *testing.T) {
 }
 
 func TestOperatorAssign(t *testing.T) {
-	tokens := token.Tokenize([]byte(`+= -= *= /= &= |= ^= <<= >>=`))
+	tokens := token.Tokenize([]byte(`a += b -= c *= d /= e &= f |= g ^= h <<= i >>= j`))
 
 	expected := []token.Kind{
+		token.Identifier,
 		token.AddAssign,
+		token.Identifier,
 		token.SubAssign,
+		token.Identifier,
 		token.MulAssign,
+		token.Identifier,
 		token.DivAssign,
+		token.Identifier,
 		token.AndAssign,
+		token.Identifier,
 		token.OrAssign,
+		token.Identifier,
 		token.XorAssign,
+		token.Identifier,
 		token.ShlAssign,
+		token.Identifier,
 		token.ShrAssign,
+		token.Identifier,
 		token.EOF,
 	}