run functions

vm/vm.go

@@ -9,30 +9,54 @@ import (
 
 const StackSize = 2048
 const GlobalsSize = 65536
+const MaxFrames = 1024
 
 var Null = &object.Null{}
 var True = &object.Boolean{Value: true}
 var False = &object.Boolean{Value: false}
 
+type Frame struct {
+	fn *object.CompiledFunction
+	ip int
+}
+
+func NewFrame(fn *object.CompiledFunction) *Frame {
+	return &Frame{fn: fn, ip: -1}
+}
+
+func (f *Frame) Instructions() code.Instructions {
+	return f.fn.Instructions
+}
+
 type VM struct {
 	constants []object.Object
-	instructions code.Instructions
 
 	stack []object.Object
 	sp    int // Always points to the next value. Top of stack is stack[sp-1]
 
 	globals []object.Object
+
+	frames      []*Frame
+	framesIndex int
 }
 
 func New(bytecode *compiler.Bytecode) *VM {
+	mainFn := &object.CompiledFunction{Instructions: bytecode.Instructions}
+	mainFrame := NewFrame(mainFn)
+
+	frames := make([]*Frame, MaxFrames)
+	frames[0] = mainFrame
+
 	return &VM{
 		constants: bytecode.Constants,
-		instructions: bytecode.Instructions,
 
 		stack: make([]object.Object, StackSize),
 		sp:    0,
 
 		globals: make([]object.Object, GlobalsSize),
+
+		frames:      frames,
+		framesIndex: 1,
 	}
 }
 
@@ -42,18 +66,40 @@ func NewWithGlobalState(bytecode *compiler.Bytecode, s []object.Object) *VM {
 	return vm
 }
 
+func (vm *VM) currentFrame() *Frame {
+	return vm.frames[vm.framesIndex-1]
+}
+
+func (vm *VM) pushFrame(f *Frame) {
+	vm.frames[vm.framesIndex] = f
+	vm.framesIndex++
+}
+
+func (vm *VM) popFrame() *Frame {
+	vm.framesIndex--
+	return vm.frames[vm.framesIndex]
+}
+
 func (vm *VM) LastPoppedStackElem() object.Object {
 	return vm.stack[vm.sp]
 }
 
 func (vm *VM) Run() error {
-	for ip := 0; ip < len(vm.instructions); ip++ {
+	var ip int
-		op := code.Opcode(vm.instructions[ip])
+	var ins code.Instructions
+	var op code.Opcode
+
+	for vm.currentFrame().ip < len(vm.currentFrame().Instructions())-1 {
+		vm.currentFrame().ip++
+
+		ip = vm.currentFrame().ip
+		ins = vm.currentFrame().Instructions()
+		op = code.Opcode(ins[ip])
 
 		switch op {
 		case code.OpConstant:
-			constIndex := code.ReadUint16(vm.instructions[ip+1:])
+			constIndex := code.ReadUint16(ins[ip+1:])
-			ip += 2
+			vm.currentFrame().ip += 2
 
 			err := vm.push(vm.constants[constIndex])
 			if err != nil {
@@ -100,16 +146,16 @@ func (vm *VM) Run() error {
 			}
 
 		case code.OpJump:
-			pos := int(code.ReadUint16(vm.instructions[ip+1:]))
+			pos := int(code.ReadUint16(ins[ip+1:]))
-			ip = pos - 1
+			vm.currentFrame().ip = pos - 1
 
 		case code.OpJumpNotTruthy:
-			pos := int(code.ReadUint16(vm.instructions[ip+1:]))
+			pos := int(code.ReadUint16(ins[ip+1:]))
-			ip += 2
+			vm.currentFrame().ip += 2
 
 			condition := vm.pop()
 			if !isTruthy(condition) {
-				ip = pos - 1
+				vm.currentFrame().ip = pos - 1
 			}
 
 		case code.OpNull:
@@ -119,14 +165,14 @@ func (vm *VM) Run() error {
 			}
 
 		case code.OpSetGlobal:
-			globalIndex := code.ReadUint16(vm.instructions[ip+1:])
+			globalIndex := code.ReadUint16(ins[ip+1:])
-			ip += 2
+			vm.currentFrame().ip += 2
 
 			vm.globals[globalIndex] = vm.pop()
 
 		case code.OpGetGlobal:
-			globalIndex := code.ReadUint16(vm.instructions[ip+1:])
+			globalIndex := code.ReadUint16(ins[ip+1:])
-			ip += 2
+			vm.currentFrame().ip += 2
 
 			err := vm.push(vm.globals[globalIndex])
 			if err != nil {
@@ -134,8 +180,8 @@ func (vm *VM) Run() error {
 			}
 
 		case code.OpArray:
-			numElements := int(code.ReadUint16(vm.instructions[ip+1:]))
+			numElements := int(code.ReadUint16(ins[ip+1:]))
-			ip += 2
+			vm.currentFrame().ip += 2
 
 			array := vm.buildArray(vm.sp-numElements, vm.sp)
 			vm.sp = vm.sp - numElements
@@ -146,8 +192,8 @@ func (vm *VM) Run() error {
 			}
 
 		case code.OpHash:
-			numElements := int(code.ReadUint16(vm.instructions[ip+1:]))
+			numElements := int(code.ReadUint16(ins[ip+1:]))
-			ip += 2
+			vm.currentFrame().ip += 2
 
 			hash, err := vm.buildHash(vm.sp-numElements, vm.sp)
 			if err != nil {
@@ -169,6 +215,33 @@ func (vm *VM) Run() error {
 				return err
 			}
 
+		case code.OpCall:
+			fn, ok := vm.stack[vm.sp-1].(*object.CompiledFunction)
+			if !ok {
+				return fmt.Errorf("calling non-function")
+			}
+			frame := NewFrame(fn)
+			vm.pushFrame(frame)
+
+		case code.OpReturnValue:
+			returnValue := vm.pop()
+			vm.popFrame()
+			vm.pop()
+
+			err := vm.push(returnValue)
+			if err != nil {
+				return err
+			}
+
+		case code.OpReturn:
+			vm.popFrame()
+			vm.pop()
+
+			err := vm.push(Null)
+			if err != nil {
+				return err
+			}
+
 		}
 	}
 

vm/vm_test.go

@@ -296,3 +296,93 @@ func TestIndexExpressions(t *testing.T) {
 
 	runVmTests(t, tests)
 }
+
+func TestCallingFunctionsWithoutArguments(t *testing.T) {
+	tests := []vmTestCase{
+		{
+			input: `
+        let fivePlusTen = fn() { 5 + 10; };
+        fivePlusTen();
+        `,
+			expected: 15,
+		},
+		{
+			input: `
+        let one = fn() { 1; };
+        let two = fn() { 2; };
+        one() + two()
+        `,
+			expected: 3,
+		},
+		{
+			input: `
+        let a = fn() { 1 };
+        let b = fn() { a() + 1 };
+        let c = fn() { b() + 1 };
+        c();
+        `,
+			expected: 3,
+		},
+	}
+
+	runVmTests(t, tests)
+}
+
+func TestFunctionsWithReturnStatements(t *testing.T) {
+	tests := []vmTestCase{
+		{
+			input: `
+        let earlyExit = fn() { return 99; 100; };
+        earlyExit();
+        `,
+			expected: 99,
+		},
+		{
+			input: `
+        let earlyExit = fn() { return 99; return 100; };
+        earlyExit();
+        `,
+			expected: 99,
+		},
+	}
+
+	runVmTests(t, tests)
+}
+
+func TestFunctionsWithoutReturnValue(t *testing.T) {
+	tests := []vmTestCase{
+		{
+			input: `
+        let noReturn = fn() { };
+        noReturn();
+        `,
+			expected: Null,
+		},
+		{
+			input: `
+        let noReturn = fn() { };
+        let noReturnTwo = fn() { noReturn(); };
+        noReturn();
+        noReturnTwo();
+        `,
+			expected: Null,
+		},
+	}
+
+	runVmTests(t, tests)
+}
+
+func TestFirstClassFunctions(t *testing.T) {
+	tests := []vmTestCase{
+		{
+			input: `
+        let returnsOne = fn() { 1; };
+        let returnsOneReturner = fn() { returnsOne; };
+        returnsOneReturner()();
+        `,
+			expected: 1,
+		},
+	}
+
+	runVmTests(t, tests)
+}