From 8caeaca559af6d119a62af0fd2d9f0a7cf7d5b4a Mon Sep 17 00:00:00 2001
From: Chuck Smith <smitty7887@gmail.com>
Date: Tue, 20 Feb 2024 16:24:59 -0500
Subject: [PATCH] VM globals

---
 compiler/compiler.go |  7 +++++++
 repl/repl.go         | 12 ++++++++++--
 vm/vm.go             | 27 +++++++++++++++++++++++++++
 vm/vm_test.go        | 10 ++++++++++
 4 files changed, 54 insertions(+), 2 deletions(-)

diff --git a/compiler/compiler.go b/compiler/compiler.go
index c3de4af..dcbd62b 100644
--- a/compiler/compiler.go
+++ b/compiler/compiler.go
@@ -32,6 +32,13 @@ func New() *Compiler {
 	}
 }
 
+func NewWithState(s *SymbolTable, constants []object.Object) *Compiler {
+	compiler := New()
+	compiler.symbolTable = s
+	compiler.constants = constants
+	return compiler
+}
+
 func (c *Compiler) Compile(node ast.Node) error {
 	switch node := node.(type) {
 	case *ast.Program:
diff --git a/repl/repl.go b/repl/repl.go
index 2c821ff..e1db9f7 100644
--- a/repl/repl.go
+++ b/repl/repl.go
@@ -6,6 +6,7 @@ import (
 	"io"
 	"monkey/compiler"
 	"monkey/lexer"
+	"monkey/object"
 	"monkey/parser"
 	"monkey/vm"
 )
@@ -15,6 +16,10 @@ const PROMPT = ">> "
 func Start(in io.Reader, out io.Writer) {
 	scanner := bufio.NewScanner(in)
 
+	constants := []object.Object{}
+	globals := make([]object.Object, vm.GlobalsSize)
+	symbolTable := compiler.NewSymbolTable()
+
 	for {
 		fmt.Fprintf(out, PROMPT)
 		scanned := scanner.Scan()
@@ -32,14 +37,17 @@ func Start(in io.Reader, out io.Writer) {
 			continue
 		}
 
-		comp := compiler.New()
+		comp := compiler.NewWithState(symbolTable, constants)
 		err := comp.Compile(program)
 		if err != nil {
 			fmt.Fprintf(out, "Woops! Compilation failed:\n %s\n", err)
 			continue
 		}
 
-		machine := vm.New(comp.Bytecode())
+		code := comp.Bytecode()
+		constants = code.Constants
+
+		machine := vm.NewWithGlobalState(comp.Bytecode(), globals)
 		err = machine.Run()
 		if err != nil {
 			fmt.Fprintf(out, "Woops! Executing bytecode failed:\n %s\n", err)
diff --git a/vm/vm.go b/vm/vm.go
index fd6e449..01803bb 100644
--- a/vm/vm.go
+++ b/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
+			}
+
 		}
 	}
 
diff --git a/vm/vm_test.go b/vm/vm_test.go
index 3821b80..757ab55 100644
--- a/vm/vm_test.go
+++ b/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)
+}