diff --git a/src/ast_printer.zig b/src/ast_printer.zig
index b770f4e..2593619 100644
--- a/src/ast_printer.zig
+++ b/src/ast_printer.zig
@@ -9,28 +9,28 @@ const warn = std.debug.warn;
 fn printIdent(ident: usize) void {
     var i: usize = 0;
     while (i < ident) : (i += 1) {
-        std.debug.warn("\t");
+        std.debug.warn("\t", .{});
     }
 }
 
-fn print(ident: usize, comptime fmt: []const u8, args: ...) void {
+fn print(ident: usize, comptime fmt: []const u8, args: var) void {
     printIdent(ident);
     std.debug.warn(fmt, args);
 }
 
 fn printBlock(ident: usize, block: var, endNewline: bool) void {
-    std.debug.warn("(\n");
+    std.debug.warn("(\n", .{});
 
     for (block.toSlice()) |stmt| {
         printIdent(ident);
         printStmt(ident, stmt);
-        std.debug.warn("\n");
+        std.debug.warn("\n", .{});
     }
 
     if (endNewline) {
-        print(ident - 1, ")\n");
+        print(ident - 1, ")\n", .{});
     } else {
-        print(ident - 1, ")");
+        print(ident - 1, ")", .{});
     }
 }
 
@@ -48,51 +48,47 @@ pub fn printNode(node: *Node, ident: usize) void {
                 const typ = method.typ.lexeme;
 
                 if (method.mutable) {
-                    warn("(method mut {} {} {} {} ", vari, typ, name, ret_type);
+                    warn("(method mut {} {} {} {} ", .{ vari, typ, name, ret_type });
                 } else {
-                    warn("(method {} {} {} {} ", vari, typ, name, ret_type);
+                    warn("(method {} {} {} {} ", .{ vari, typ, name, ret_type });
                 }
             } else {
-                warn("(fn {} {} (", name, ret_type);
+                warn("(fn {} {} (", .{ name, ret_type });
             }
 
             for (decl.params.toSlice()) |param| {
-                warn("({} {}) ", param.name.lexeme, param.typ.lexeme);
+                warn("({} {}) ", .{ param.name.lexeme, param.typ.lexeme });
             }
 
             printBlock(ident + 1, decl.body, false);
-            warn(")\n");
+            warn(")\n", .{});
         },
 
         .ConstDecl => |consts| {
-            print(ident, "(const (\n");
+            print(ident, "(const (\n", .{});
 
             for (consts.toSlice()) |const_decl| {
-                print(
-                    ident + 1,
-                    "({} ",
+                print(ident + 1, "({} ", .{
                     const_decl.name.lexeme,
-                );
+                });
 
                 printExpr(const_decl.expr);
-                std.debug.warn(")\n");
+                std.debug.warn(")\n", .{});
             }
 
-            print(ident, "))\n");
+            print(ident, "))\n", .{});
         },
 
         .Enum => |decl| {
-            print(ident, "(enum {} (\n", decl.name.lexeme);
+            print(ident, "(enum {} (\n", .{decl.name.lexeme});
 
             for (decl.fields.toSlice()) |field| {
-                print(
-                    ident + 1,
-                    "{}\n",
+                print(ident + 1, "{}\n", .{
                     field.lexeme,
-                );
+                });
             }
 
-            print(ident, "))\n");
+            print(ident, "))\n", .{});
         },
 
         .Root => {
@@ -104,129 +100,129 @@ pub fn printNode(node: *Node, ident: usize) void {
         .Stmt => |stmt| {
             printIdent(ident);
             printStmt(ident, stmt);
-            std.debug.warn("\n");
+            std.debug.warn("\n", .{});
         },
 
         .Struct => |struc| {
-            print(ident, "(struct {} (\n", struc.name.lexeme);
+            print(ident, "(struct {} (\n", .{struc.name.lexeme});
             for (struc.fields.toSlice()) |field| {
                 printIdent(ident + 1);
                 if (field.mutable) {
-                    std.debug.warn("(mut ");
+                    std.debug.warn("(mut ", .{});
                 } else {
-                    std.debug.warn("(");
+                    std.debug.warn("(", .{});
                 }
 
                 if (field.public) {
-                    std.debug.warn("pub ");
+                    std.debug.warn("pub ", .{});
                 }
 
                 if (field.mutable_outside) {
-                    std.debug.warn("MUT_OUT ");
+                    std.debug.warn("MUT_OUT ", .{});
                 }
 
-                std.debug.warn("{} {})\n", field.name.lexeme, field.typ.lexeme);
+                std.debug.warn("{} {})\n", .{ field.name.lexeme, field.typ.lexeme });
             }
-            print(ident, "))\n");
+            print(ident, "))\n", .{});
         },
 
         else => {
-            print(ident, "unknown node: {}\n", node);
+            print(ident, "unknown node: {}\n", .{node});
         },
     }
 }
 
-fn parenthetize(name: []const u8, exprs: []*Expr) void {
-    std.debug.warn("({}", name);
+fn parenthetize(name: []const u8, exprs: []*const Expr) void {
+    std.debug.warn("({}", .{name});
 
     for (exprs) |expr| {
-        std.debug.warn(" ");
+        std.debug.warn(" ", .{});
         printExpr(expr);
     }
 
-    std.debug.warn(")");
+    std.debug.warn(")", .{});
 }
 
-pub fn printExpr(expr: *Expr) void {
+pub fn printExpr(expr: *const Expr) void {
     switch (expr.*) {
-        .Binary => |binary| parenthetize(binary.op.lexeme, &[_]*Expr{ binary.left, binary.right }),
-        .Logical => |binary| parenthetize(binary.op.lexeme, &[_]*Expr{ binary.left, binary.right }),
-        .Unary => |unary| parenthetize(unary.op.lexeme, &[_]*Expr{unary.right}),
-        .Grouping => |expr_ptr| parenthetize("group", &[_]*Expr{expr_ptr}),
+        .Binary => |binary| parenthetize(binary.op.lexeme, &[_]*const Expr{ binary.left, binary.right }),
+        .Logical => |binary| parenthetize(binary.op.lexeme, &[_]*const Expr{ binary.left, binary.right }),
+        .Unary => |unary| parenthetize(unary.op.lexeme, &[_]*const Expr{unary.right}),
+        .Grouping => |expr_ptr| parenthetize("group", &[_]*const Expr{expr_ptr}),
 
         .Literal => |literal| {
             switch (literal) {
-                .Bool => |val| std.debug.warn("{}", val),
-                .Integer => |val| std.debug.warn("{}", val),
-                .Float => |val| std.debug.warn("{}", val),
-                .String => |val| std.debug.warn("'{}'", val),
+                .Bool => |val| std.debug.warn("{}", .{val}),
+                .Integer => |val| std.debug.warn("{}", .{val}),
+                .Float => |val| std.debug.warn("{}", .{val}),
+                .String => |val| std.debug.warn("'{}'", .{val}),
                 .Array => |exprs| {
                     parenthetize("array", exprs.toSlice());
                 },
-                else => |typ| std.debug.warn("UnknownLiteral-{}", typ),
+                else => |typ| std.debug.warn("UnknownLiteral-{}", .{typ}),
             }
         },
 
-        .Variable => |token| std.debug.warn("{}", token.lexeme),
+        .Variable => |token| std.debug.warn("{}", .{token.lexeme}),
 
         .VarDecl => |decl| {
             if (decl.mutable) {
-                std.debug.warn("(mut ");
+                std.debug.warn("(mut ", .{});
             } else {
-                std.debug.warn("(");
+                std.debug.warn("(", .{});
             }
 
-            std.debug.warn("let {} ", decl.assign.name.lexeme);
+            std.debug.warn("let {} ", .{decl.assign.name.lexeme});
             printExpr(decl.assign.value);
-            std.debug.warn(")");
+            std.debug.warn(")", .{});
         },
 
         .Assign => |assign| {
-            std.debug.warn("(set ");
-            std.debug.warn("{} ", assign.name.lexeme);
+            std.debug.warn("(set ", .{});
+            std.debug.warn("{} ", .{assign.name.lexeme});
             printExpr(assign.value);
-            std.debug.warn(")");
+            std.debug.warn(")", .{});
         },
 
         .Call => |call| {
-            std.debug.warn("(");
+            std.debug.warn("(", .{});
             printExpr(call.callee);
 
             for (call.arguments.toSlice()) |arg| {
-                std.debug.warn(" ");
+                std.debug.warn(" ", .{});
                 printExpr(arg);
             }
 
-            std.debug.warn(")");
+            std.debug.warn(")", .{});
         },
 
         .Struct => |val| {
-            std.debug.warn("({} (", val.name.lexeme);
+            std.debug.warn("({} (", .{val.name.lexeme});
 
             for (val.inits.toSlice()) |init| {
-                std.debug.warn(" ({} ", init.field.lexeme);
+                std.debug.warn(" ({} ", .{init.field.lexeme});
                 printExpr(init.expr);
-                std.debug.warn(")");
+                std.debug.warn(")", .{});
             }
 
-            std.debug.warn("))");
+            std.debug.warn("))", .{});
         },
 
         .Get => |get| {
-            warn("(");
+            warn("(", .{});
             printExpr(get.struc);
-            warn(".{})", get.name.lexeme);
+            warn("{}", .{get.name.lexeme});
         },
 
         .Set => |set| {
-            warn("(set ");
+            warn("(set ", .{});
             printExpr(set.struc);
-            warn(" {} ", set.field.lexeme);
+            warn(" {} ", .{set.field.lexeme});
             printExpr(set.value);
-            warn(")");
+            warn(")", .{});
         },
 
-        else => std.debug.warn("UnknownExpr-{}", @tagName(expr.*)),
+        else => std.debug.warn("UnknownExpr-{}", .{@tagName(expr.*)}),
     }
 }
 
@@ -236,53 +232,53 @@ pub fn printStmt(ident: usize, stmt: *Stmt) void {
         .Expr => |expr| printExpr(expr),
 
         .If => |ifstmt| {
-            std.debug.warn("(if ");
+            std.debug.warn("(if ", .{});
             printExpr(ifstmt.condition);
-            std.debug.warn(" ");
+            std.debug.warn(" ", .{});
 
             printBlock(ident + 1, ifstmt.then_branch, false);
             if (ifstmt.else_branch) |else_branch| {
-                std.debug.warn(" else ");
+                std.debug.warn(" else ", .{});
                 printBlock(ident + 1, else_branch, false);
             }
 
-            std.debug.warn(")\n");
+            std.debug.warn(")\n", .{});
         },
 
         .Loop => |loop| {
-            std.debug.warn("(loop ");
+            std.debug.warn("(loop ", .{});
             if (loop.condition) |cond| {
                 printExpr(cond);
             } else {
-                std.debug.warn("true");
+                std.debug.warn("true", .{});
             }
-            std.debug.warn(" ");
+            std.debug.warn(" ", .{});
 
             printBlock(ident + 1, loop.then_branch, false);
-            std.debug.warn(")\n");
+            std.debug.warn(")\n", .{});
         },
 
         .For => |forstmt| {
-            std.debug.warn("(for ");
+            std.debug.warn("(for ", .{});
 
             if (forstmt.index) |index| {
-                std.debug.warn("({} {}) ", index.lexeme, forstmt.value.lexeme);
+                std.debug.warn("({} {}) ", .{ index.lexeme, forstmt.value.lexeme });
             } else {
-                std.debug.warn("{} ", forstmt.value.lexeme);
+                std.debug.warn("{} ", .{forstmt.value.lexeme});
             }
 
-            std.debug.warn("{} ", forstmt.array.lexeme);
+            std.debug.warn("{} ", .{forstmt.array.lexeme});
 
             printBlock(ident + 1, forstmt.block, false);
-            std.debug.warn(")\n");
+            std.debug.warn(")\n", .{});
         },
 
         .Return => |ret| {
-            std.debug.warn("(return ");
+            std.debug.warn("(return ", .{});
             printExpr(ret.value);
-            std.debug.warn(")\n");
+            std.debug.warn(")\n", .{});
         },
 
-        else => std.debug.warn("UnknownStmt-{}", @tagName(stmt.*)),
+        else => std.debug.warn("UnknownStmt-{}", .{@tagName(stmt.*)}),
     }
 }
diff --git a/src/errors.zig b/src/errors.zig
index 201afb0..eb95d27 100644
--- a/src/errors.zig
+++ b/src/errors.zig
@@ -1,14 +1,14 @@
 const std = @import("std");
 pub fn report(line: usize, where: []const u8, message: []const u8) void {
-    std.debug.warn("[line {}] Error{}: {}", line, where, message);
+    std.debug.warn("[line {}] Error{}: {}", .{ line, where, message });
 }
 
 pub fn reportN(line: usize, message: []const u8) void {
     report(line, "", message);
 }
 
-pub fn reportFmt(line: usize, comptime fmt: []const u8, args: ...) void {
-    std.debug.warn("[line {}] Error", line);
+pub fn reportFmt(line: usize, comptime fmt: []const u8, args: var) void {
+    std.debug.warn("[line {}] Error", .{line});
     std.debug.warn(fmt, args);
-    std.debug.warn("\n");
+    std.debug.warn("\n", .{});
 }
diff --git a/src/main.zig b/src/main.zig
index 47e3a53..f2c6156 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -10,18 +10,16 @@ pub const Result = error{
     CompileError,
 };
 
-pub const StdOut = *std.io.OutStream(std.fs.File.WriteError);
-
-fn run(allocator: *Allocator, data: []u8) !void {
+fn run(allocator: *Allocator, data: []const u8) !void {
     var stdout_file = std.io.getStdOut();
-    const stdout = &stdout_file.outStream().stream;
+    const stdout = stdout_file.outStream();
 
     var runner = runners.Runner.init(allocator, stdout);
     return runner.execute(data);
 }
 
 fn runFile(allocator: *Allocator, path: []const u8) !void {
-    var file = try std.fs.File.openRead(path);
+    var file = try std.fs.cwd().openFile(path, .{});
     defer file.close();
 
     const total_bytes = try file.getEndPos();
@@ -40,25 +38,31 @@ fn runFile(allocator: *Allocator, path: []const u8) !void {
 
 fn runPrompt(allocator: *Allocator) !void {
     var stdout_file = std.io.getStdOut();
-    const stdout = &stdout_file.outStream().stream;
+    const stdout = stdout_file.outStream();
+
+    var stdin_file = std.io.getStdIn();
+    const stdin = stdin_file.inStream();
+
+    var line_buf: [1024]u8 = undefined;
 
     while (true) {
-        try stdout.print("> ");
-        var buffer = try std.Buffer.init(allocator, ""[0..]);
+        try stdout.print("> ", .{});
 
-        var line = std.io.readLine(&buffer) catch |err| {
-            if (err == error.EndOfStream) return;
-            return err;
-        };
+        const amt = try stdin.read(&line_buf);
+        if (amt == line_buf.len) {
+            try stdout.print("Input too long.\n", .{});
+            continue;
+        }
+        const line = std.mem.trimRight(u8, line_buf[0..amt], "\r\n");
 
         run(allocator, line) catch |err| {
             switch (err) {
                 Result.Ok => {},
                 Result.ScannerError => blk: {
-                    try stdout.print("scanner error.\n");
+                    try stdout.print("scanner error.\n", .{});
                 },
                 Result.CompileError => blk: {
-                    try stdout.print("compile error.\n");
+                    try stdout.print("compile error.\n", .{});
                 },
                 else => return err,
             }
@@ -67,12 +71,12 @@ fn runPrompt(allocator: *Allocator) !void {
 }
 
 pub fn main() anyerror!void {
-    var arena = std.heap.ArenaAllocator.init(std.heap.direct_allocator);
+    var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
     defer arena.deinit();
     var allocator = &arena.allocator;
 
     var stdout_file = std.io.getStdOut();
-    var stdout = &stdout_file.outStream().stream;
+    var stdout = stdout_file.outStream();
 
     var args_it = std.process.args();
 
diff --git a/src/parser.zig b/src/parser.zig
index 46976e2..818a540 100644
--- a/src/parser.zig
+++ b/src/parser.zig
@@ -43,27 +43,27 @@ pub const Parser = struct {
         self.tokens.deinit();
     }
 
-    fn doError(self: *Parser, comptime fmt: []const u8, args: ...) void {
+    fn doError(self: *Parser, comptime fmt: []const u8, args: var) void {
         self.hadError = true;
 
-        std.debug.warn("parser error at line {}\n\t", self.scanner.line);
+        std.debug.warn("parser error at line {}\n\t", .{self.scanner.line});
         std.debug.warn(fmt, args);
-        std.debug.warn("\n");
+        std.debug.warn("\n", .{});
     }
 
     fn peek(self: *Parser) Token {
-        return self.tokens.at(self.tokens.len - 1);
+        return self.tokens.items[self.tokens.items.len - 1];
     }
 
     fn previous(self: *Parser) Token {
-        return self.tokens.at(self.tokens.len - 2);
+        return self.tokens.items[self.tokens.items.len - 2];
     }
 
     fn tokenError(self: *Parser, token: Token, msg: []const u8) Result!void {
         if (token.ttype == .EOF) {
             err.report(token.line, " at end", msg);
         } else {
-            err.reportFmt(token.line, " at '{}': {}", token.lexeme, msg);
+            err.reportFmt(token.line, " at '{}': {}", .{ token.lexeme, msg });
         }
 
         return Result.CompileError;
@@ -90,7 +90,7 @@ pub const Parser = struct {
         }
 
         try self.tokens.append(token);
-        std.debug.warn("skip to {}\n", token);
+        std.debug.warn("skip to {}\n", .{token});
         return token;
     }
 
@@ -117,19 +117,17 @@ pub const Parser = struct {
 
         // TODO maybe this could be entirely comptime?
         var buf_main: [1000]u8 = undefined;
-        var buf = try std.fmt.bufPrint(
-            buf_main[0..],
-            "expected {}, got {}",
+        var buf = try std.fmt.bufPrint(buf_main[0..], "expected {}, got {}", .{
             ttype,
             self.peek().ttype,
-        );
+        });
 
         try self.tokenError(self.peek(), buf);
         return Result.CompileError;
     }
 
     /// check() against multiple tokens
-    fn compareAnyOf(self: *@This(), ttypes: []TokenType) bool {
+    fn compareAnyOf(self: *@This(), ttypes: []const TokenType) bool {
         for (ttypes) |ttype| {
             if (self.check(ttype)) return true;
         }
@@ -191,7 +189,7 @@ pub const Parser = struct {
     }
 
     fn mkUnary(self: *Parser, op: Token, right: *Expr) !*Expr {
-        std.debug.warn("Unary\n");
+        std.debug.warn("Unary\n", .{});
 
         var expr = try self.allocator.create(Expr);
         expr.* = Expr{
@@ -609,7 +607,7 @@ pub const Parser = struct {
             .Enum => try self.parseEnumDecl(),
 
             else => |ttype| blk: {
-                self.doError("expected Fn, Const, Struct, got {}\n", ttype);
+                self.doError("expected Fn, Const, Struct, got {}\n", .{ttype});
                 return Result.CompileError;
             },
         };
@@ -839,7 +837,7 @@ pub const Parser = struct {
             .Get => |get| {
                 switch (op.ttype) {
                     .ColonEqual => {
-                        self.doError("can not initialize struct field");
+                        self.doError("can not initialize struct field", .{});
                         return Result.CompileError;
                     },
 
@@ -859,7 +857,7 @@ pub const Parser = struct {
             },
 
             else => |expr_typ| {
-                self.doError("Invalid assignment target {}", expr_typ);
+                self.doError("Invalid assignment target {}", .{expr_typ});
                 return Result.CompileError;
             },
         }
@@ -1030,7 +1028,7 @@ pub const Parser = struct {
         // <expr>{a: 10 b: 10}
         // for this to work properly, <expr> must be Variable, since its a type.
         if (@as(ast.ExprType, expr.*) != .Variable) {
-            self.doError("Expected variable for struct type, got {}", @as(ast.ExprType, expr.*));
+            self.doError("Expected variable for struct type, got {}", .{@as(ast.ExprType, expr.*)});
             return Result.CompileError;
         }
 
@@ -1095,7 +1093,7 @@ pub const Parser = struct {
             },
 
             else => blk: {
-                self.doError("expected literal, got {}", curtype);
+                self.doError("expected literal, got {}", .{curtype});
                 return Result.CompileError;
             },
         };
diff --git a/src/runner.zig b/src/runner.zig
index 9c9f0f5..49b0dd4 100644
--- a/src/runner.zig
+++ b/src/runner.zig
@@ -13,32 +13,31 @@ const Parser = parsers.Parser;
 
 pub const Runner = struct {
     allocator: *Allocator,
-    stdout: main.StdOut,
+    stdout: std.fs.File.OutStream,
 
-    pub fn init(allocator: *Allocator, stdout: main.StdOut) Runner {
-        return Runner{ .allocator = allocator, .stdout = stdout };
+    pub fn init(allocator: *Allocator, stdout: var) Runner {
+        return .{ .allocator = allocator, .stdout = stdout };
     }
 
     fn testScanner(self: *Runner, scanner: *scanners.Scanner) !void {
         while (true) {
             var tok_opt = scanner.nextToken() catch |err| {
-                try self.stdout.print(
-                    "error at '{}': {}\n",
+                try self.stdout.print("error at '{}': {}\n", .{
                     scanner.currentLexeme(),
                     err,
-                );
+                });
 
                 return Result.ScannerError;
             };
 
             if (tok_opt) |tok| {
                 if (tok.ttype == .EOF) break;
-                try self.stdout.print("{x}\n", tok);
+                try self.stdout.print("{x}\n", .{tok});
             }
         }
     }
 
-    pub fn execute(self: *Runner, code: []u8) !void {
+    pub fn execute(self: *Runner, code: []const u8) !void {
         var scanner = scanners.Scanner.init(self.allocator, code);
         try self.testScanner(&scanner);
 
@@ -46,9 +45,9 @@ pub const Runner = struct {
         var parser = Parser.init(self.allocator, &scanner);
         var root = try parser.parse();
 
-        var it = root.Root.iterator();
+        // var it = root.Root.iterator();
 
-        std.debug.warn("parse tree\n");
+        std.debug.warn("parse tree\n", .{});
         printer.printNode(root, 0);
 
         return Result.Ok;
diff --git a/src/scanner.zig b/src/scanner.zig
index 0261a7a..907dd48 100644
--- a/src/scanner.zig
+++ b/src/scanner.zig
@@ -97,13 +97,13 @@ fn getKeyword(keyword: []const u8) ?TokenType {
 /// Scanner for vlang tokens.
 pub const Scanner = struct {
     allocator: *Allocator,
-    source: []u8,
+    source: []const u8,
 
     start: usize = 0,
     current: usize = 0,
     line: usize = 1,
 
-    pub fn init(allocator: *Allocator, source: []u8) Scanner {
+    pub fn init(allocator: *Allocator, source: []const u8) Scanner {
         return Scanner{ .allocator = allocator, .source = source };
     }