diff --git a/examples/hello/hello.q b/examples/hello/hello.q
index e5101a2..2981aa1 100644
--- a/examples/hello/hello.q
+++ b/examples/hello/hello.q
@@ -1,4 +1,8 @@
 main() {
-	syscall(1, 1, 4194305, 3)
-	syscall(60, 0)
+	let write = 1
+	let exit = 60
+	let stdout = 1
+
+	syscall(write, stdout, 4194305, 3)
+	syscall(exit, 0)
 }
\ No newline at end of file
diff --git a/src/build/Function.go b/src/build/Function.go
index 729c5c5..8044009 100644
--- a/src/build/Function.go
+++ b/src/build/Function.go
@@ -16,6 +16,7 @@ type Function struct {
 	Name      string
 	Head      token.List
 	Body      token.List
+	Variables map[string]*Variable
 	Assembler asm.Assembler
 }
 
@@ -36,6 +37,16 @@ func (f *Function) Compile() {
 
 		if line[0].Kind == token.Keyword {
 			switch line[0].Text() {
+			case "let":
+				name := line[1].Text()
+				value := line[3:]
+				fmt.Println("[variable]", name, value)
+
+				f.Variables[name] = &Variable{
+					Value:   line[3:],
+					IsConst: true,
+				}
+
 			case "return":
 				f.Assembler.Return()
 			}
@@ -61,16 +72,33 @@ func (f *Function) Compile() {
 			}
 
 			for i, list := range parameters {
-				if list[0].Kind == token.Number {
-					numAsText := list[0].Text()
-					n, _ := strconv.Atoi(numAsText)
+				switch list[0].Kind {
+				case token.Identifier:
+					name := list[0].Text()
+					variable := f.Variables[name]
+
+					if !variable.IsConst {
+						panic("Not implemented yet")
+					}
+
+					n, _ := strconv.Atoi(variable.Value[0].Text())
 					f.Assembler.MoveRegisterNumber(x64.SyscallArgs[i], uint64(n))
+
+				case token.Number:
+					value := list[0].Text()
+					n, _ := strconv.Atoi(value)
+					f.Assembler.MoveRegisterNumber(x64.SyscallArgs[i], uint64(n))
+
+				default:
+					panic("Unknown expression")
 				}
 			}
 
 			f.Assembler.Syscall()
 		}
 	}
+
+	f.Assembler.Return()
 }
 
 // Lines returns the lines in the function body.
diff --git a/src/build/Scan.go b/src/build/Scan.go
index 6c56628..318c598 100644
--- a/src/build/Scan.go
+++ b/src/build/Scan.go
@@ -215,9 +215,10 @@ func scanFile(path string, functions chan<- *Function) error {
 		}
 
 		functions <- &Function{
-			Name: tokens[nameStart].Text(),
-			Head: tokens[paramsStart:bodyStart],
-			Body: tokens[bodyStart : i+1],
+			Name:      tokens[nameStart].Text(),
+			Head:      tokens[paramsStart:bodyStart],
+			Body:      tokens[bodyStart : i+1],
+			Variables: map[string]*Variable{},
 		}
 
 		nameStart = -1
diff --git a/src/build/Variable.go b/src/build/Variable.go
new file mode 100644
index 0000000..14cece9
--- /dev/null
+++ b/src/build/Variable.go
@@ -0,0 +1,9 @@
+package build
+
+import "git.akyoto.dev/cli/q/src/build/token"
+
+// Variable represents a variable in a function.
+type Variable struct {
+	Value   token.List
+	IsConst bool
+}
diff --git a/src/build/token/Keywords.go b/src/build/token/Keywords.go
index adb8de7..a8eec3c 100644
--- a/src/build/token/Keywords.go
+++ b/src/build/token/Keywords.go
@@ -2,5 +2,6 @@ package token
 
 // Keywords defines the keywords used in the language.
 var Keywords = map[string]bool{
+	"let":    true,
 	"return": true,
 }
diff --git a/src/build/token/List.go b/src/build/token/List.go
index 4c5953e..9cef514 100644
--- a/src/build/token/List.go
+++ b/src/build/token/List.go
@@ -13,7 +13,7 @@ func (list List) String() string {
 	var last Token
 
 	for _, t := range list {
-		if t.Kind == Identifier && last.Kind == Separator {
+		if last.Kind == Keyword || last.Kind == Separator {
 			builder.WriteByte(' ')
 		}
 
diff --git a/src/build/token/Tokenize.go b/src/build/token/Tokenize.go
index 213adb6..53cdbb6 100644
--- a/src/build/token/Tokenize.go
+++ b/src/build/token/Tokenize.go
@@ -70,6 +70,9 @@ func Tokenize(buffer []byte) List {
 		case ']':
 			tokens = append(tokens, Token{ArrayEnd, i, arrayEndBytes})
 
+		case '=', ':', '+', '-', '*', '/', '<', '>', '!':
+			tokens = append(tokens, Token{Operator, i, buffer[i : i+1]})
+
 		// Separator
 		case ',':
 			tokens = append(tokens, Token{Separator, i, separatorBytes})
@@ -147,3 +150,7 @@ func isNumber(c byte) bool {
 func isNumberStart(c byte) bool {
 	return isNumber(c) || c == '-'
 }
+
+func isOperator(c byte) bool {
+	return c == '=' || c == ':' || c == '+' || c == '-' || c == '*' || c == '/' || c == '<' || c == '>' || c == '!'
+}