VM globals

vm/vm.go

@@ -8,6 +8,7 @@ import (
 )
 
 const StackSize = 2048
+const GlobalsSize = 65536
 
 var Null = &object.Null{}
 var True = &object.Boolean{Value: true}
@@ -19,6 +20,8 @@ type VM struct {
 
 	stack []object.Object
 	sp    int // Always points to the next value. Top of stack is stack[sp-1]
+
+	globals []object.Object
 }
 
 func New(bytecode *compiler.Bytecode) *VM {
@@ -28,9 +31,17 @@ func New(bytecode *compiler.Bytecode) *VM {
 
 		stack: make([]object.Object, StackSize),
 		sp:    0,
+
+		globals: make([]object.Object, GlobalsSize),
 	}
 }
 
+func NewWithGlobalState(bytecode *compiler.Bytecode, s []object.Object) *VM {
+	vm := New(bytecode)
+	vm.globals = s
+	return vm
+}
+
 func (vm *VM) LastPoppedStackElem() object.Object {
 	return vm.stack[vm.sp]
 }
@@ -106,6 +117,22 @@ func (vm *VM) Run() error {
 			if err != nil {
 				return err
 			}
+
+		case code.OpSetGlobal:
+			globalIndex := code.ReadUint16(vm.instructions[ip+1:])
+			ip += 2
+
+			vm.globals[globalIndex] = vm.pop()
+
+		case code.OpGetGlobal:
+			globalIndex := code.ReadUint16(vm.instructions[ip+1:])
+			ip += 2
+
+			err := vm.push(vm.globals[globalIndex])
+			if err != nil {
+				return err
+			}
+
 		}
 	}
 

vm/vm_test.go

@@ -165,3 +165,13 @@ func TestConditionals(t *testing.T) {
 
 	runVmTests(t, tests)
 }
+
+func TestGlobalLetStatements(t *testing.T) {
+	tests := []vmTestCase{
+		{"let one = 1; one", 1},
+		{"let one = 1; let two = 2; one + two", 3},
+		{"let one = 1; let two = one + one; one + two", 3},
+	}
+
+	runVmTests(t, tests)
+}