Feat: add instruction limit in run program

program.go

@@ -18,3 +18,7 @@ func (p *Program) defineLit(v Value) uint {
 	p.values = append(p.values, v)
 	return index
 }
+
+func (p *Program) InstructionNumber() int {
+	return len(p.code)
+}

runtime.go

@@ -77,6 +77,10 @@ func (r *Runtime) Global() *Global {
 	return r.global
 }
 
+func (r *Runtime) SetCyclesLimit(max int) {
+	r.vm.cyclesLimit = max
+}
+
 func (r *Runtime) RunProgram(ctx context.Context, program *Program) (Value, error) {
 	r.vm.program = program
 	r.vm.pc = 0

runtime_test.go

@@ -210,6 +210,35 @@ func TestRunExamples(t *testing.T) {
 	}
 }
 
+func TestExceedInstructionLimit(t *testing.T) {
+	src := `
+	(function (x) {
+		return function (f) {
+			return function () {
+				return f(x(x)(f))();
+			};
+		};
+	})(function (x) {
+		return function (f) {
+			return function () {
+				return f(x(x)(f))();
+			};
+		};
+	})(function (f) {
+		return function () {
+			return f();
+		};
+	})()
+`
+
+	r := New()
+	r.SetCyclesLimit(5)
+	_, err := r.RunString(src)
+	if err != ErrCyclesLimitExceeded {
+		t.Errorf("cycles limit exceeded expected")
+	}
+}
+
 func BenchmarkRunProgram(b *testing.B) {
 	program, err := Compile(`"hello"[0] + 1 && false`)
 	if err != nil {

vm.go

@@ -26,7 +26,10 @@ type ctx struct {
 	pc, bp  int
 }
 
-var ErrStackOverflow = errors.New("stack overflow")
+var (
+	ErrStackOverflow       = errors.New("stack overflow")
+	ErrCyclesLimitExceeded = errors.New("cycles limit exceeded")
+)
 
 func (v *valueStack) init() {
 	v.l = v.l[:0]
@@ -106,6 +109,8 @@ type vm struct {
 	callStack []ctx
 	bp        int
 	program   *Program
+
+	cyclesLimit int
 }
 
 func (vm *vm) newStash() {
@@ -136,11 +141,18 @@ func (vm *vm) run() (err error) {
 
 	vm.halt = false
 	ctx := vm.ctx
+	remainingCycles := vm.cyclesLimit
+
 	for !vm.halt {
 		select {
 		case <-ctx.Done():
 			return ctx.Err()
 		default:
+			if remainingCycles > 0 {
+				if remainingCycles--; remainingCycles == 0 {
+					return ErrCyclesLimitExceeded
+				}
+			}
 		}
 		vm.program.code[vm.pc].exec(vm)
 	}