diff --git a/examples/thread/thread.q b/examples/thread/thread.q
index 6d0493b..91d5689 100644
--- a/examples/thread/thread.q
+++ b/examples/thread/thread.q
@@ -2,9 +2,10 @@ import io
 import thread
 
 main() {
-	thread.create(work)
-	thread.create(work)
-	thread.create(work)
+	loop 0..3 {
+		thread.create(work)
+	}
+
 	work()
 }
 
diff --git a/src/ast/Loop.go b/src/ast/Loop.go
index e1ca210..4d7257c 100644
--- a/src/ast/Loop.go
+++ b/src/ast/Loop.go
@@ -1,6 +1,9 @@
 package ast
 
+import "git.akyoto.dev/cli/q/src/expression"
+
 // Loop represents a block of repeatable statements.
 type Loop struct {
+	Head *expression.Expression
 	Body AST
 }
diff --git a/src/ast/parseKeyword.go b/src/ast/parseKeyword.go
index 32c2bbd..9c2cd9b 100644
--- a/src/ast/parseKeyword.go
+++ b/src/ast/parseKeyword.go
@@ -40,8 +40,15 @@ func parseKeyword(tokens token.List, source []byte, nodes AST) (Node, error) {
 		return nil, err
 
 	case token.Loop:
-		_, _, body, err := block(tokens, source)
-		return &Loop{Body: body}, err
+		blockStart, _, body, err := block(tokens, source)
+		head := tokens[1:blockStart]
+
+		loop := &Loop{
+			Head: expression.Parse(head),
+			Body: body,
+		}
+
+		return loop, err
 
 	case token.Return:
 		if len(tokens) == 1 {
diff --git a/src/core/ArrayElementToRegister.go b/src/core/ArrayElementToRegister.go
index 46e24f7..c623035 100644
--- a/src/core/ArrayElementToRegister.go
+++ b/src/core/ArrayElementToRegister.go
@@ -46,6 +46,8 @@ func (f *Function) ArrayElementToRegister(node *expression.Expression, register
 			return nil, errors.New(&errors.UnknownIdentifier{Name: indexName}, f.File, index.Token.Position)
 		}
 
+		defer f.UseVariable(indexVariable)
+
 		if !types.Is(indexVariable.Type, types.Int) {
 			return nil, errors.New(&errors.TypeMismatch{Encountered: indexVariable.Type.Name(), Expected: types.Int.Name()}, f.File, index.Token.Position)
 		}
diff --git a/src/core/CompileLoop.go b/src/core/CompileLoop.go
index f2ef623..1209fe1 100644
--- a/src/core/CompileLoop.go
+++ b/src/core/CompileLoop.go
@@ -5,21 +5,92 @@ import (
 
 	"git.akyoto.dev/cli/q/src/asm"
 	"git.akyoto.dev/cli/q/src/ast"
+	"git.akyoto.dev/cli/q/src/cpu"
+	"git.akyoto.dev/cli/q/src/expression"
+	"git.akyoto.dev/cli/q/src/token"
 )
 
 // CompileLoop compiles a loop instruction.
 func (f *Function) CompileLoop(loop *ast.Loop) error {
+	if loop.Head == nil {
+		return f.CompileLoopInfinite(loop)
+	}
+
 	for _, register := range f.CPU.Input {
 		f.SaveRegister(register)
 	}
 
 	f.count.loop++
-	label := fmt.Sprintf("%s_loop_%d", f.UniqueName, f.count.loop)
-	f.AddLabel(label)
+
+	var (
+		label    = fmt.Sprintf("%s_loop_%d", f.UniqueName, f.count.loop)
+		labelEnd = fmt.Sprintf("%s_loop_%d_end", f.UniqueName, f.count.loop)
+		counter  cpu.Register
+		from     *expression.Expression
+		to       *expression.Expression
+	)
+
 	scope := f.PushScope(loop.Body, f.File.Bytes)
 	scope.InLoop = true
-	err := f.CompileAST(loop.Body)
+
+	switch loop.Head.Token.Kind {
+	case token.Define:
+		variable, err := f.Define(loop.Head.Children[0])
+
+		if err != nil {
+			return err
+		}
+
+		counter = variable.Register
+		from = loop.Head.Children[1].Children[0]
+		to = loop.Head.Children[1].Children[1]
+		f.AddVariable(variable)
+
+	case token.Range:
+		counter = f.NewRegister()
+		defer f.FreeRegister(counter)
+		from = loop.Head.Children[0]
+		to = loop.Head.Children[1]
+
+	default:
+		panic("could not recognize loop header")
+	}
+
+	_, err := f.ExpressionToRegister(from, counter)
+
+	if err != nil {
+		return err
+	}
+
+	if to.Token.IsNumeric() {
+		number, err := f.ToNumber(to.Token)
+
+		if err != nil {
+			return err
+		}
+
+		f.AddLabel(label)
+		f.RegisterNumber(asm.COMPARE, counter, number)
+	} else {
+		_, register, isTemporary, err := f.Evaluate(to)
+
+		if err != nil {
+			return err
+		}
+
+		if isTemporary {
+			defer f.FreeRegister(register)
+		}
+
+		f.AddLabel(label)
+		f.RegisterRegister(asm.COMPARE, counter, register)
+	}
+
+	f.Jump(asm.JGE, labelEnd)
+	err = f.CompileAST(loop.Body)
+	f.RegisterNumber(asm.ADD, counter, 1)
 	f.Jump(asm.JUMP, label)
+	f.AddLabel(labelEnd)
 	f.PopScope()
 	return err
 }
diff --git a/src/core/CompileLoopInfinite.go b/src/core/CompileLoopInfinite.go
new file mode 100644
index 0000000..e8eada3
--- /dev/null
+++ b/src/core/CompileLoopInfinite.go
@@ -0,0 +1,25 @@
+package core
+
+import (
+	"fmt"
+
+	"git.akyoto.dev/cli/q/src/asm"
+	"git.akyoto.dev/cli/q/src/ast"
+)
+
+// CompileLoopInfinite compiles an infinite loop.
+func (f *Function) CompileLoopInfinite(loop *ast.Loop) error {
+	for _, register := range f.CPU.Input {
+		f.SaveRegister(register)
+	}
+
+	f.count.loop++
+	label := fmt.Sprintf("%s_loop_%d", f.UniqueName, f.count.loop)
+	f.AddLabel(label)
+	scope := f.PushScope(loop.Body, f.File.Bytes)
+	scope.InLoop = true
+	err := f.CompileAST(loop.Body)
+	f.Jump(asm.JUMP, label)
+	f.PopScope()
+	return err
+}
diff --git a/src/core/Define.go b/src/core/Define.go
index 94f7428..d017d85 100644
--- a/src/core/Define.go
+++ b/src/core/Define.go
@@ -10,7 +10,7 @@ import (
 // Define defines a new variable.
 func (f *Function) Define(leaf *expression.Expression) (*scope.Variable, error) {
 	name := leaf.Token.Text(f.File.Bytes)
-	variable, _ := f.Identifier(name)
+	variable := f.VariableByName(name)
 
 	if variable != nil {
 		return nil, errors.New(&errors.VariableAlreadyExists{Name: name}, f.File, leaf.Token.Position)
diff --git a/src/core/Evaluate.go b/src/core/Evaluate.go
index cd3f384..68da992 100644
--- a/src/core/Evaluate.go
+++ b/src/core/Evaluate.go
@@ -2,6 +2,7 @@ package core
 
 import (
 	"git.akyoto.dev/cli/q/src/cpu"
+	"git.akyoto.dev/cli/q/src/errors"
 	"git.akyoto.dev/cli/q/src/expression"
 	"git.akyoto.dev/cli/q/src/token"
 	"git.akyoto.dev/cli/q/src/types"
@@ -13,6 +14,10 @@ func (f *Function) Evaluate(expr *expression.Expression) (types.Type, cpu.Regist
 		name := expr.Token.Text(f.File.Bytes)
 		variable := f.VariableByName(name)
 
+		if variable == nil {
+			return nil, 0, false, errors.New(&errors.UnknownIdentifier{Name: name}, f.File, expr.Token.Position)
+		}
+
 		if variable.Alive == 1 {
 			f.UseVariable(variable)
 			return variable.Type, variable.Register, false, nil
diff --git a/src/expression/Operator.go b/src/expression/Operator.go
index f69ba00..800277a 100644
--- a/src/expression/Operator.go
+++ b/src/expression/Operator.go
@@ -41,6 +41,7 @@ var Operators = [64]Operator{
 	token.LogicalAnd:   {"&&", 2, 2},
 	token.LogicalOr:    {"||", 1, 2},
 
+	token.Range:     {"..", 0, 2},
 	token.Separator: {",", 0, 2},
 
 	token.Assign:    {"=", math.MinInt8, 2},
diff --git a/src/token/Kind.go b/src/token/Kind.go
index 200d131..54feac0 100644
--- a/src/token/Kind.go
+++ b/src/token/Kind.go
@@ -34,6 +34,7 @@ const (
 	LogicalOr                         // ||
 	Define                            // :=
 	Period                            // .
+	Range                             // ..
 	Call                              // x()
 	Array                             // [x]
 	Separator                         // ,
diff --git a/src/token/operator.go b/src/token/operator.go
index 46251ad..5d74059 100644
--- a/src/token/operator.go
+++ b/src/token/operator.go
@@ -36,6 +36,8 @@ func operator(tokens List, buffer []byte, i Position) (List, Position) {
 		kind = AddAssign
 	case ".":
 		kind = Period
+	case "..":
+		kind = Range
 	case ":=":
 		kind = Define
 	case "<":
diff --git a/tests/programs/array-index-dynamic.q b/tests/programs/array-index-dynamic.q
deleted file mode 100644
index 4e4c03f..0000000
--- a/tests/programs/array-index-dynamic.q
+++ /dev/null
@@ -1,23 +0,0 @@
-import mem
-
-main() {
-	a := mem.alloc(4)
-	i := 0
-
-	a[i] = i * 2
-	i += 1
-	a[i] = i * 2
-	i += 1
-	a[i] = i * 2
-	i += 1
-	a[i] = i * 2
-
-	i = 0
-	assert a[i] == i * 2
-	i += 1
-	assert a[i] == i * 2
-	i += 1
-	assert a[i] == i * 2
-	i += 1
-	assert a[i] == i * 2
-}
\ No newline at end of file
diff --git a/tests/programs/index-dynamic.q b/tests/programs/index-dynamic.q
new file mode 100644
index 0000000..7f1cfe3
--- /dev/null
+++ b/tests/programs/index-dynamic.q
@@ -0,0 +1,10 @@
+import mem
+
+main() {
+	a := mem.alloc(4)
+
+	loop i := 0..4 {
+		a[i] = i * 2
+		assert a[i] == i * 2
+	}
+}
\ No newline at end of file
diff --git a/tests/programs/array-index-static.q b/tests/programs/index-static.q
similarity index 100%
rename from tests/programs/array-index-static.q
rename to tests/programs/index-static.q
diff --git a/tests/programs/loop.q b/tests/programs/loop-infinite.q
similarity index 100%
rename from tests/programs/loop.q
rename to tests/programs/loop-infinite.q
diff --git a/tests/programs/loop-limited.q b/tests/programs/loop-limited.q
new file mode 100644
index 0000000..c26975c
--- /dev/null
+++ b/tests/programs/loop-limited.q
@@ -0,0 +1,6 @@
+main() {
+	loop i := 0..10 {
+		assert i >= 0
+		assert i < 10
+	}
+}
\ No newline at end of file
diff --git a/tests/programs_test.go b/tests/programs_test.go
index 32bf77e..15e5e30 100644
--- a/tests/programs_test.go
+++ b/tests/programs_test.go
@@ -57,12 +57,13 @@ var programs = []struct {
 	{"branch-save", "", "", 0},
 	{"jump-near", "", "", 0},
 	{"switch", "", "", 0},
-	{"loop", "", "", 0},
+	{"loop-infinite", "", "", 0},
 	{"loop-lifetime", "", "", 0},
+	{"loop-limited", "", "", 0},
 	{"memory-free", "", "", 0},
 	{"out-of-memory", "", "", 0},
-	{"array-index-static", "", "", 0},
-	{"array-index-dynamic", "", "", 0},
+	{"index-static", "", "", 0},
+	{"index-dynamic", "", "", 0},
 	{"struct", "", "", 0},
 	{"len", "", "", 0},
 }