diff --git a/src/ast.zig b/src/ast.zig
index 5886e8a..7588cc7 100644
--- a/src/ast.zig
+++ b/src/ast.zig
@@ -1,27 +1,63 @@
-pub const AstNodeType = enum {
-    Program,
-    BinOp,
+const tokens = @import("tokens.zig");
+const Token = tokens.Token;
+
+pub const ExprType = enum {
+    Unary,
+    Binary,
+    Grouping,
     Number,
 };
 
-pub const AstNode = union(AstNodeType) {
-    Program: []AstNode,
-    BinOp: AstBinOp,
-    Number: AstNumber,
+pub const Expr = union(ExprType) {
+    Unary: UnaryExpr,
+    Binary: BinaryExpr,
+    Grouping: Grouping,
+    Number: Number,
 };
 
-pub const BinOpType = enum {
-    Equality,
+pub const UnaryExpr = struct {
+    operator: Token,
+    right: *Expr,
 };
 
-pub const AstBinOp = struct {
-    optype: BinOpType,
+pub fn mkUnary(operator: Token, right: *Expr) Expr {
+    return Expr{
+        .Unary = UnaryExpr{
+            .operator = operator,
+            .right = right,
+        },
+    };
+}
 
-    // TODO expression
-    left: *AstNode,
-    right: *AstNode,
+pub const BinaryExpr = struct {
+    left: *Expr,
+    operator: Token,
+    right: *Expr,
 };
 
+pub fn mkBinary(left: *Expr, operator: Token, right: *Expr) Expr {
+    return Expr{
+        .Binary = BinaryExpr{
+            .left = left,
+            .operator = operator,
+            .right = right,
+        },
+    };
+}
+
+pub const Grouping = struct {
+    expression: *Expr,
+};
+
+pub fn mkGrouping(expression: *Expr) Expr {
+    return Expr{
+        .Grouping = Grouping{
+            .expression = expression,
+        },
+    };
+}
+
+/// Represents the default number literals in V.
 pub const NumberType = enum {
     Integer32,
     Integer64,
@@ -31,7 +67,9 @@ pub const NumberType = enum {
     Float64,
 };
 
-pub const AstNumber = union(NumberType) {
+/// "translation" of V number types to Zig number types for nicer
+/// representation.
+pub const Number = union(NumberType) {
     Integer32: i32,
     Integer64: i64,
     Unsigned32: u32,
@@ -40,41 +78,16 @@ pub const AstNumber = union(NumberType) {
     Float64: f64,
 };
 
-pub fn printNode(stdout: var, node: AstNode) anyerror!void {
-    switch (node) {
-        .Program => |children| try printNodes(stdout, children),
-        .BinOp => |bin_op| blk: {
-            try stdout.print("(");
-            switch (bin_op.optype) {
-                .Equality => try stdout.write("=="),
-            }
+pub fn mkNum(comptime T: type, num: T) Expr {
+    var expr = switch (T) {
+        i32 => Expr{ .Number = Number{ .Integer32 = num } },
+        i64 => Expr{ .Number = Number{ .Integer64 = num } },
+        u32 => Expr{ .Number = Number{ .Unsigned32 = num } },
+        u64 => Expr{ .Number = Number{ .Unsigned64 = num } },
+        f32 => Expr{ .Number = Number{ .Float32 = num } },
+        f64 => Expr{ .Number = Number{ .Float64 = num } },
+        else => unreachable,
+    };
 
-            try stdout.write(" ");
-            try printNode(stdout, bin_op.left.*);
-            try stdout.write(" ");
-            try printNode(stdout, bin_op.right.*);
-            try stdout.print(")");
-        },
-        .Number => |ast_num| {
-            switch (ast_num) {
-                .Integer32 => |num| try stdout.print("{}", num),
-                .Integer64 => |num| try stdout.print("{}", num),
-                .Unsigned32 => |num| try stdout.print("{}", num),
-                .Unsigned64 => |num| try stdout.print("{}", num),
-                .Float32 => |num| try stdout.print("{}", num),
-                .Float64 => |num| try stdout.print("{}", num),
-            }
-        },
-    }
-}
-
-fn printNodes(stdout: var, nodes: []AstNode) anyerror!void {
-    try stdout.print("(");
-
-    for (nodes) |node| {
-        try stdout.print(" ");
-        try printNode(stdout, node);
-    }
-
-    try stdout.print(")");
+    return expr;
 }
diff --git a/src/ast_printer.zig b/src/ast_printer.zig
new file mode 100644
index 0000000..ae1a9b7
--- /dev/null
+++ b/src/ast_printer.zig
@@ -0,0 +1,32 @@
+const std = @import("std");
+const ast = @import("ast.zig");
+
+fn parenthesize(name: []const u8, exprs: []*ast.Expr) void {
+    std.debug.warn("({}", name);
+
+    for (exprs) |expr| {
+        std.debug.warn(" ");
+        printAst(expr);
+    }
+
+    std.debug.warn(")");
+}
+
+pub fn printAst(ast_expr: *ast.Expr) void {
+    switch (ast_expr.*) {
+        .Binary => |expr| parenthesize(expr.operator.lexeme, &[]*ast.Expr{ expr.left, expr.right }),
+        .Grouping => |expr| parenthesize("group", &[]*ast.Expr{expr.expression}),
+        .Unary => |expr| parenthesize(expr.operator.lexeme, &[]*ast.Expr{expr.right}),
+        .Number => |ast_num| {
+            switch (ast_num) {
+                .Integer32 => |num| std.debug.warn("{}", num),
+                .Integer64 => |num| std.debug.warn("{}", num),
+                .Unsigned32 => |num| std.debug.warn("{}", num),
+                .Unsigned64 => |num| std.debug.warn("{}", num),
+                .Float32 => |num| std.debug.warn("{}", num),
+                .Float64 => |num| std.debug.warn("{}", num),
+            }
+        },
+        else => unreachable,
+    }
+}
diff --git a/src/runner.zig b/src/runner.zig
index 5e0bb1b..209842d 100644
--- a/src/runner.zig
+++ b/src/runner.zig
@@ -4,6 +4,9 @@ const parsers = @import("parser.zig");
 const main = @import("main.zig");
 const ast = @import("ast.zig");
 
+const tokens = @import("tokens.zig");
+const printer = @import("ast_printer.zig");
+
 const Allocator = std.mem.Allocator;
 const Result = main.Result;
 const Parser = parsers.Parser;
@@ -42,24 +45,18 @@ pub const Runner = struct {
         scanner = scanners.Scanner.init(self.allocator, code);
         //var parser = Parser.init(self.allocator, &scanner);
         //var tree = try parser.parse();
-        try ast.printNode(self.stdout, ast.AstNode{
-            .Program = &[]ast.AstNode{ast.AstNode{
-                .BinOp = ast.AstBinOp{
-                    .optype = ast.BinOpType.Equality,
-                    .left = &ast.AstNode{
-                        .Number = ast.AstNumber{
-                            .Integer32 = 30,
-                        },
-                    },
-                    .right = &ast.AstNode{
-                        .Number = ast.AstNumber{
-                            .Integer32 = 30,
-                        },
-                    },
-                },
-            }},
-        });
-        try self.stdout.print("\n");
+
+        var expr = ast.mkBinary(
+            &ast.mkUnary(
+                tokens.Token{ .ttype = .Minus, .lexeme = "-", .line = 1 },
+                &ast.mkNum(i32, 123),
+            ),
+            tokens.Token{ .ttype = .Star, .lexeme = "*", .line = 1 },
+            &ast.mkGrouping(&ast.mkNum(f32, 45.67)),
+        );
+
+        printer.printAst(&expr);
+        std.debug.warn("\n");
 
         return Result.Ok;
     }