main: keep a long-running vm instance for REPL

enables us to declare variables and keep them going for as long as the
REPL goes.

 - vm: remove source arg from init(), move to interpret()

src/main.zig

@@ -16,9 +16,17 @@ fn run(allocator: *Allocator, data: []u8) !void {
     var stdout_file = try std.io.getStdOut();
     const stdout = &stdout_file.outStream().stream;
 
-    var vmach = try vm.VM.init(allocator, stdout, data, true);
+    var vmach = try vm.VM.init(allocator, stdout, true);
     defer vmach.deinit();
-    try vmach.interpret();
+    try vmach.interpret(data);
+}
+
+fn runWithVM(vmach: *vm.VM, data: []u8) !void {
+    var stdout_file = try std.io.getStdOut();
+    const stdout = &stdout_file.outStream().stream;
+
+    defer vmach.deinit();
+    try vmach.interpret(data);
 }
 
 pub fn doError(line: usize, message: []const u8) !void {
@@ -55,6 +63,9 @@ fn runPrompt(allocator: *Allocator) !void {
     var stdout_file = try std.io.getStdOut();
     const stdout = &stdout_file.outStream().stream;
 
+    var vmach = try vm.VM.init(allocator, stdout, true);
+    defer vmach.deinit();
+
     while (true) {
         try stdout.print(">");
         var buffer = try std.Buffer.init(allocator, ""[0..]);
@@ -65,7 +76,7 @@ fn runPrompt(allocator: *Allocator) !void {
             return err;
         };
 
-        run(allocator, line) catch |err| {
+        runWithVM(&vmach, line) catch |err| {
             switch (err) {
                 InterpretResult.Ok => {},
                 InterpretResult.CompileError, InterpretResult.RuntimeError => blk: {

src/vm.zig

@@ -40,7 +40,6 @@ pub const ValueMap = std.AutoHashMap([]const u8, values.Value);
 
 pub const VM = struct {
     chk: *Chunk = undefined,
-    src: []const u8,
     ip: usize = 0,
 
     stack: []Value,
@@ -60,12 +59,9 @@ pub const VM = struct {
     pub fn init(
         allocator: *std.mem.Allocator,
         stdout: StdOut,
-        source: []const u8,
         debug_flag: bool,
     ) !VM {
         var self = VM{
-            .src = source,
-
             .stack = try allocator.alloc(Value, 256),
             .stdout = stdout,
             .debug_flag = debug_flag,
@@ -352,7 +348,7 @@ pub const VM = struct {
         }
     }
 
-    pub fn interpret(self: *VM) !void {
+    pub fn interpret(self: *VM, src: []const u8) !void {
         //self.ip = 0;
         //self.debug("VM start\n");
         //var res = try self.run();
@@ -364,7 +360,7 @@ pub const VM = struct {
             self.allocator,
             &chk,
             self.stdout,
-            self.src,
+            src,
             self.debug_flag,
             self,
         );