diff --git a/examples/hello/hello.q b/examples/hello/hello.q
index ef15401..afd5576 100644
--- a/examples/hello/hello.q
+++ b/examples/hello/hello.q
@@ -1,8 +1,4 @@
 main() {
-	hello()
-}
-
-hello() {
 	address := 0
 	length := 0
 
@@ -15,6 +11,7 @@ hello() {
 	length *= 10
 	length /= 100
 	length = (0 + 50 - 20) * 10 / 100
+	length = 1
 
 	loop {
 		print(address, length)
@@ -22,7 +19,7 @@ hello() {
 }
 
 print(address, length) {
-	write(1, address, length)
+	write(length, address, length+1)
 }
 
 write(fd, address, length) {
diff --git a/src/build/Execute.go b/src/build/Execute.go
index 84e51d6..d636bed 100644
--- a/src/build/Execute.go
+++ b/src/build/Execute.go
@@ -33,6 +33,32 @@ func (f *Function) Execute(operation token.Token, register cpu.Register, value *
 	return f.ExecuteRegisterRegister(operation, register, temporary)
 }
 
+// ExecuteFunctionCall executes a function call.
+func (f *Function) ExecuteFunctionCall(expr *expression.Expression) error {
+	funcName := expr.Children[0].Token.Text()
+	parameters := expr.Children[1:]
+
+	if funcName == "syscall" {
+		err := f.ExpressionsToRegisters(parameters, f.CPU.Syscall)
+
+		if err != nil {
+			return err
+		}
+
+		f.Assembler.Syscall()
+	} else {
+		err := f.ExpressionsToRegisters(parameters, f.CPU.Call)
+
+		if err != nil {
+			return err
+		}
+
+		f.Assembler.Call(funcName)
+	}
+
+	return nil
+}
+
 // ExecuteLeaf performs an operation on a register with the given leaf operand.
 func (f *Function) ExecuteLeaf(operation token.Token, register cpu.Register, operand token.Token) error {
 	switch operand.Kind {
diff --git a/src/build/Function.go b/src/build/Function.go
index ba070c2..fadb68b 100644
--- a/src/build/Function.go
+++ b/src/build/Function.go
@@ -113,7 +113,7 @@ func (f *Function) CompileInstruction(line token.List) error {
 	}
 
 	if isFunctionCall(expr) {
-		return f.CompileFunctionCall(expr)
+		return f.ExecuteFunctionCall(expr)
 	}
 
 	return errors.New(&errors.InvalidInstruction{Instruction: expr.Token.Text()}, f.File, expr.Token.Position)
@@ -139,6 +139,19 @@ func (f *Function) ExpressionToRegister(root *expression.Expression, register cp
 	return f.Execute(operation, register, right)
 }
 
+// ExpressionsToRegisters moves multiple expressions into the specified registers.
+func (f *Function) ExpressionsToRegisters(expressions []*expression.Expression, registers []cpu.Register) error {
+	for i := len(expressions) - 1; i >= 0; i-- {
+		err := f.ExpressionToRegister(expressions[i], registers[i])
+
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
 // TokenToRegister moves a token into a register.
 // It only works with identifiers, numbers and strings.
 func (f *Function) TokenToRegister(t token.Token, register cpu.Register) error {
diff --git a/src/build/FunctionCall.go b/src/build/FunctionCall.go
deleted file mode 100644
index 8f2c2ea..0000000
--- a/src/build/FunctionCall.go
+++ /dev/null
@@ -1,32 +0,0 @@
-package build
-
-import (
-	"git.akyoto.dev/cli/q/src/build/expression"
-)
-
-// CompileFunctionCall compiles a top-level function call.
-func (f *Function) CompileFunctionCall(expr *expression.Expression) error {
-	funcName := expr.Children[0].Token.Text()
-	parameters := expr.Children[1:]
-	registers := f.CPU.Syscall
-
-	if funcName != "syscall" {
-		registers = registers[1:]
-	}
-
-	for i := len(parameters) - 1; i >= 0; i-- {
-		err := f.ExpressionToRegister(parameters[i], registers[i])
-
-		if err != nil {
-			return err
-		}
-	}
-
-	if funcName == "syscall" {
-		f.Assembler.Syscall()
-	} else {
-		f.Assembler.Call(funcName)
-	}
-
-	return nil
-}
diff --git a/src/build/VariableDefinition.go b/src/build/VariableDefinition.go
index 270b8e1..b7ac7ca 100644
--- a/src/build/VariableDefinition.go
+++ b/src/build/VariableDefinition.go
@@ -29,12 +29,12 @@ func (f *Function) CompileVariableDefinition(expr *expression.Expression) error
 		return err
 	}
 
-	f.CPU.Use(reg)
-
-	f.Variables[name] = &Variable{
+	variable := &Variable{
 		Name:     name,
 		Register: reg,
 	}
 
+	f.Variables[name] = variable
+	f.CPU.Use(reg)
 	return nil
 }
diff --git a/src/build/arch/x64/Registers.go b/src/build/arch/x64/Registers.go
index da154af..44807c4 100644
--- a/src/build/arch/x64/Registers.go
+++ b/src/build/arch/x64/Registers.go
@@ -21,6 +21,9 @@ const (
 	R15
 )
 
-var GeneralRegisters = []cpu.Register{RBX, RBP, R12, R13, R14, R15}
-var SyscallRegisters = []cpu.Register{RAX, RDI, RSI, RDX, R10, R8, R9}
-var ReturnValueRegisters = []cpu.Register{RAX, RCX, R11}
+var (
+	CallRegisters        = []cpu.Register{RDI, RSI, RDX, RCX, R8, R9}
+	GeneralRegisters     = []cpu.Register{RBX, RBP, R12, R13, R14, R15}
+	SyscallRegisters     = []cpu.Register{RAX, RDI, RSI, RDX, R10, R8, R9}
+	ReturnValueRegisters = []cpu.Register{RAX, RCX, R11}
+)
diff --git a/src/build/cpu/CPU.go b/src/build/cpu/CPU.go
index f6a6f9b..0092154 100644
--- a/src/build/cpu/CPU.go
+++ b/src/build/cpu/CPU.go
@@ -2,6 +2,7 @@ package cpu
 
 // CPU represents the processor.
 type CPU struct {
+	Call    []Register
 	General []Register
 	Syscall []Register
 	Return  []Register
diff --git a/src/build/scan.go b/src/build/scan.go
index af81199..f9b7ea0 100644
--- a/src/build/scan.go
+++ b/src/build/scan.go
@@ -225,6 +225,7 @@ func scanFile(path string, functions chan<- *Function) error {
 		}
 
 		cpu := cpu.CPU{
+			Call:    x64.CallRegisters,
 			General: x64.GeneralRegisters,
 			Syscall: x64.SyscallRegisters,
 			Return:  x64.ReturnValueRegisters,