diff --git a/README.md b/README.md
index 8598efb..70e1ea5 100644
--- a/README.md
+++ b/README.md
@@ -124,6 +124,7 @@ This is what generates expressions from tokens.
 ### Keywords
 
 - [x] `assert`
+- [x] `else`
 - [ ] `for`
 - [x] `if`
 - [x] `import`
diff --git a/examples/factorial/factorial.q b/examples/factorial/factorial.q
index 30315ec..dab665c 100644
--- a/examples/factorial/factorial.q
+++ b/examples/factorial/factorial.q
@@ -1,7 +1,7 @@
-import sys
+import log
 
 main() {
-	sys.exit(factorial(5))
+	log.number(factorial(5))
 }
 
 factorial(x) {
diff --git a/examples/fibonacci/fibonacci.q b/examples/fibonacci/fibonacci.q
index 505bf26..acc3e78 100644
--- a/examples/fibonacci/fibonacci.q
+++ b/examples/fibonacci/fibonacci.q
@@ -1,7 +1,7 @@
-import sys
+import log
 
 main() {
-	sys.exit(fibonacci(10))
+	log.number(fibonacci(10))
 }
 
 fibonacci(x) {
diff --git a/examples/gcd/gcd.q b/examples/gcd/gcd.q
new file mode 100644
index 0000000..9e9b5e0
--- /dev/null
+++ b/examples/gcd/gcd.q
@@ -0,0 +1,19 @@
+import log
+
+main() {
+	log.number(gcd(1071, 462))
+}
+
+gcd(a, b) {
+	loop {
+		if a == b {
+			return a
+		}
+
+		if a > b {
+			a -= b
+		} else {
+			b -= a
+		}
+	}
+}
\ No newline at end of file
diff --git a/src/build/ast/EachInstruction.go b/src/build/ast/EachInstruction.go
index f11bedc..b4d9d8a 100644
--- a/src/build/ast/EachInstruction.go
+++ b/src/build/ast/EachInstruction.go
@@ -39,6 +39,18 @@ func EachInstruction(body token.List, call func(token.List) error) error {
 
 		case token.BlockEnd:
 			blockLevel--
+
+			if groupLevel > 0 || blockLevel > 0 {
+				continue
+			}
+
+			err := call(body[start : i+1])
+
+			if err != nil {
+				return err
+			}
+
+			start = i + 1
 		}
 	}
 
diff --git a/src/build/ast/If.go b/src/build/ast/If.go
index 4275f34..f99307f 100644
--- a/src/build/ast/If.go
+++ b/src/build/ast/If.go
@@ -8,4 +8,5 @@ import (
 type If struct {
 	Condition *expression.Expression
 	Body      AST
+	Else      AST
 }
diff --git a/src/build/ast/Parse.go b/src/build/ast/Parse.go
index 2c6fd94..582f497 100644
--- a/src/build/ast/Parse.go
+++ b/src/build/ast/Parse.go
@@ -7,19 +7,19 @@ import (
 
 // Parse generates an AST from a list of tokens.
 func Parse(tokens []token.Token, source []byte) (AST, error) {
-	tree := make(AST, 0, len(tokens)/64)
+	nodes := make(AST, 0, len(tokens)/64)
 
 	err := EachInstruction(tokens, func(instruction token.List) error {
-		node, err := parseNode(instruction, source)
+		node, err := parseNode(instruction, source, nodes)
 
 		if err == nil && node != nil {
-			tree = append(tree, node)
+			nodes = append(nodes, node)
 		}
 
 		return err
 	})
 
-	return tree, err
+	return nodes, err
 }
 
 // IsAssignment returns true if the expression is an assignment.
diff --git a/src/build/ast/parseKeyword.go b/src/build/ast/parseKeyword.go
index f8aa676..a123570 100644
--- a/src/build/ast/parseKeyword.go
+++ b/src/build/ast/parseKeyword.go
@@ -7,7 +7,7 @@ import (
 )
 
 // parseKeyword generates a keyword node from an instruction.
-func parseKeyword(tokens token.List, source []byte) (Node, error) {
+func parseKeyword(tokens token.List, source []byte, nodes AST) (Node, error) {
 	switch tokens[0].Kind {
 	case token.Assert:
 		if len(tokens) == 1 {
@@ -22,6 +22,23 @@ func parseKeyword(tokens token.List, source []byte) (Node, error) {
 		condition := expression.Parse(tokens[1:blockStart])
 		return &If{Condition: condition, Body: body}, err
 
+	case token.Else:
+		_, _, body, err := block(tokens, source)
+
+		if len(nodes) == 0 {
+			return nil, errors.New(errors.ExpectedIfBeforeElse, nil, tokens[0].Position)
+		}
+
+		last := nodes[len(nodes)-1]
+		ifNode, exists := last.(*If)
+
+		if !exists {
+			return nil, errors.New(errors.ExpectedIfBeforeElse, nil, tokens[0].Position)
+		}
+
+		ifNode.Else = body
+		return nil, err
+
 	case token.Loop:
 		_, _, body, err := block(tokens, source)
 		return &Loop{Body: body}, err
diff --git a/src/build/ast/parseNode.go b/src/build/ast/parseNode.go
index 9ea7174..8473c29 100644
--- a/src/build/ast/parseNode.go
+++ b/src/build/ast/parseNode.go
@@ -7,9 +7,9 @@ import (
 )
 
 // parseNode generates an AST node from an instruction.
-func parseNode(tokens token.List, source []byte) (Node, error) {
+func parseNode(tokens token.List, source []byte, nodes AST) (Node, error) {
 	if tokens[0].IsKeyword() {
-		return parseKeyword(tokens, source)
+		return parseKeyword(tokens, source, nodes)
 	}
 
 	expr := expression.Parse(tokens)
diff --git a/src/build/core/CompileIf.go b/src/build/core/CompileIf.go
index 3eeb4ae..6b1a869 100644
--- a/src/build/core/CompileIf.go
+++ b/src/build/core/CompileIf.go
@@ -3,15 +3,20 @@ package core
 import (
 	"fmt"
 
+	"git.akyoto.dev/cli/q/src/build/asm"
 	"git.akyoto.dev/cli/q/src/build/ast"
 )
 
 // CompileIf compiles a branch instruction.
 func (f *Function) CompileIf(branch *ast.If) error {
 	f.count.branch++
-	success := fmt.Sprintf("%s_if_%d_true", f.Name, f.count.branch)
-	fail := fmt.Sprintf("%s_if_%d_false", f.Name, f.count.branch)
-	err := f.CompileCondition(branch.Condition, success, fail)
+
+	var (
+		end     string
+		success = fmt.Sprintf("%s_if_%d_true", f.Name, f.count.branch)
+		fail    = fmt.Sprintf("%s_if_%d_false", f.Name, f.count.branch)
+		err     = f.CompileCondition(branch.Condition, success, fail)
+	)
 
 	if err != nil {
 		return err
@@ -20,7 +25,31 @@ func (f *Function) CompileIf(branch *ast.If) error {
 	f.AddLabel(success)
 	f.PushScope(branch.Body, f.File.Bytes)
 	err = f.CompileAST(branch.Body)
+
+	if err != nil {
+		return err
+	}
+
+	if branch.Else != nil {
+		end = fmt.Sprintf("%s_if_%d_end", f.Name, f.count.branch)
+		f.Jump(asm.JUMP, end)
+	}
+
 	f.PopScope()
 	f.AddLabel(fail)
-	return err
+
+	if branch.Else != nil {
+		f.PushScope(branch.Else, f.File.Bytes)
+		err = f.CompileAST(branch.Else)
+
+		if err != nil {
+			return err
+		}
+
+		f.PopScope()
+		f.AddLabel(end)
+		return nil
+	}
+
+	return nil
 }
diff --git a/src/build/errors/CompileErrors.go b/src/build/errors/CompileErrors.go
index 5f65804..a214de3 100644
--- a/src/build/errors/CompileErrors.go
+++ b/src/build/errors/CompileErrors.go
@@ -1,12 +1,13 @@
 package errors
 
 var (
-	InvalidNumber       = &Base{"Invalid number"}
-	InvalidExpression   = &Base{"Invalid expression"}
-	InvalidRune         = &Base{"Invalid rune"}
-	InvalidStatement    = &Base{"Invalid statement"}
-	MissingExpression   = &Base{"Missing expression"}
-	MissingMainFunction = &Base{"Missing main function"}
-	MissingOperand      = &Base{"Missing operand"}
-	NotImplemented      = &Base{"Not implemented"}
+	ExpectedIfBeforeElse = &Base{"Expected an 'if' block before 'else'"}
+	InvalidNumber        = &Base{"Invalid number"}
+	InvalidExpression    = &Base{"Invalid expression"}
+	InvalidRune          = &Base{"Invalid rune"}
+	InvalidStatement     = &Base{"Invalid statement"}
+	MissingExpression    = &Base{"Missing expression"}
+	MissingMainFunction  = &Base{"Missing main function"}
+	MissingOperand       = &Base{"Missing operand"}
+	NotImplemented       = &Base{"Not implemented"}
 )
diff --git a/src/build/token/Kind.go b/src/build/token/Kind.go
index 44f0132..2c12464 100644
--- a/src/build/token/Kind.go
+++ b/src/build/token/Kind.go
@@ -20,6 +20,7 @@ const (
 	ArrayEnd                    // ]
 	_keywords                   // <keywords>
 	Assert                      // assert
+	Else                        // else
 	If                          // if
 	Import                      // import
 	Loop                        // loop
diff --git a/src/build/token/Tokenize.go b/src/build/token/Tokenize.go
index 929eff3..c955e9a 100644
--- a/src/build/token/Tokenize.go
+++ b/src/build/token/Tokenize.go
@@ -143,6 +143,8 @@ func Tokenize(buffer []byte) List {
 					kind = Assert
 				case "if":
 					kind = If
+				case "else":
+					kind = Else
 				case "import":
 					kind = Import
 				case "loop":
diff --git a/tests/errors/ExpectedIfBeforeElse.q b/tests/errors/ExpectedIfBeforeElse.q
new file mode 100644
index 0000000..a4a7018
--- /dev/null
+++ b/tests/errors/ExpectedIfBeforeElse.q
@@ -0,0 +1,3 @@
+main() {
+	else {}
+}
\ No newline at end of file
diff --git a/tests/errors/ExpectedIfBeforeElse2.q b/tests/errors/ExpectedIfBeforeElse2.q
new file mode 100644
index 0000000..a2b575f
--- /dev/null
+++ b/tests/errors/ExpectedIfBeforeElse2.q
@@ -0,0 +1,4 @@
+main() {
+	loop {}
+	else {}
+}
\ No newline at end of file
diff --git a/tests/errors_test.go b/tests/errors_test.go
index 5b28ee2..88f6b3f 100644
--- a/tests/errors_test.go
+++ b/tests/errors_test.go
@@ -17,6 +17,8 @@ var errs = []struct {
 	{"ExpectedFunctionDefinition.q", errors.ExpectedFunctionDefinition},
 	{"ExpectedFunctionName.q", errors.ExpectedFunctionName},
 	{"ExpectedFunctionParameters.q", errors.ExpectedFunctionParameters},
+	{"ExpectedIfBeforeElse.q", errors.ExpectedIfBeforeElse},
+	{"ExpectedIfBeforeElse2.q", errors.ExpectedIfBeforeElse},
 	{"InvalidInstructionIdentifier.q", &errors.InvalidInstruction{Instruction: "abc"}},
 	{"InvalidInstructionNumber.q", &errors.InvalidInstruction{Instruction: "123"}},
 	{"InvalidInstructionExpression.q", &errors.InvalidInstruction{Instruction: "+"}},
diff --git a/tests/examples_test.go b/tests/examples_test.go
index 5c2ee12..94d5f80 100644
--- a/tests/examples_test.go
+++ b/tests/examples_test.go
@@ -16,8 +16,9 @@ var examples = []struct {
 	ExitCode int
 }{
 	{"hello", "", "Hello", 0},
-	{"factorial", "", "", 120},
-	{"fibonacci", "", "", 55},
+	{"factorial", "", "120", 0},
+	{"fibonacci", "", "55", 0},
+	{"gcd", "", "21", 0},
 	{"array", "", "Hello", 0},
 	{"echo", "Echo", "Echo", 0},
 	{"itoa", "", "9223372036854775807", 0},