diff --git a/ast.cpp b/ast.cpp
index 3002657..6d8cf8b 100644
--- a/ast.cpp
+++ b/ast.cpp
@@ -2,6 +2,26 @@
 
 namespace dsp {
 
+void ast_printer_t::visit(const unary_t * unary) const
+{
+  parenthesize((unary->oper).lexeme, unary->expr);
+}
+
+void ast_printer_t::visit(const binary_t * binary) const
+{
+  parenthesize((binary->oper).lexeme, binary->left, binary->right);
+}
+
+void ast_printer_t::visit(const grouping_t * grouping) const
+{
+  parenthesize(std::string_view("<grouping>"), grouping->expr);
+}
+
+void ast_printer_t::visit(const literal_t * literal) const
+{
+  os << std::to_string(literal->value);
+}
+
 void ast_printer_t::parenthesize(const std::string_view s, const expr_t * a) const
 {
   os << '(' << s << ' ';
@@ -18,14 +38,4 @@ void ast_printer_t::parenthesize(const std::string_view s, const expr_t * a, con
   os << ')';
 }
 
-void ast_printer_t::visit(const literal_t * literal) const
-{
-  os << std::to_string(literal->value);
-}
-
-void ast_printer_t::visit(const assign_t * expr) const
-{
-  parenthesize((expr->name).lexeme, &(expr->value));
-}
-
 }
diff --git a/ast.hpp b/ast.hpp
index 21e2487..b1d3ad2 100644
--- a/ast.hpp
+++ b/ast.hpp
@@ -16,7 +16,9 @@ struct ast_printer_t : visitor_t<void>
 
   std::ostream& os;
 
-  void visit(const assign_t * expr) const;
+  void visit(const unary_t * unary) const;
+  void visit(const binary_t * binary) const;
+  void visit(const grouping_t * grouping) const;
   void visit(const literal_t * literal) const;
 
   void parenthesize(const std::string_view s, const expr_t * a) const;
diff --git a/expr.hpp b/expr.hpp
index 86e38f2..bb179c6 100644
--- a/expr.hpp
+++ b/expr.hpp
@@ -24,13 +24,22 @@ struct expr_accept_t : expr_t {
     }
 };
 
-struct assign_t : expr_accept_t<assign_t>
+struct binary_t : expr_accept_t<binary_t>
 {
-  assign_t(token_t& name, expr_t& value)
-    : name(name), value(value) {}
+  binary_t(expr_t * left, token_t oper, expr_t * right)
+    : left(left), oper(oper), right(right) {}
 
-  const token_t name;
-  const expr_t& value;
+  const expr_t * left;
+  const token_t oper;
+  const expr_t * right;
+};
+
+struct grouping_t : expr_accept_t<grouping_t>
+{
+  grouping_t(expr_t * expr)
+    : expr(expr) {}
+
+  const expr_t * expr;
 };
 
 struct literal_t : expr_accept_t<literal_t>
@@ -41,4 +50,13 @@ struct literal_t : expr_accept_t<literal_t>
   const num_t value;
 };
 
+struct unary_t : expr_accept_t<unary_t>
+{
+  unary_t(token_t oper, expr_t * expr)
+    : oper(oper), expr(expr) {}
+
+  const token_t oper;
+  const expr_t * expr;
+};
+
 }
diff --git a/main.cpp b/main.cpp
index 2472531..544e9ac 100644
--- a/main.cpp
+++ b/main.cpp
@@ -15,9 +15,9 @@ bool had_error = false;
 static void print()
 {
   dsp::literal_t l(56);
-  std::string_view s("asdf");
-  dsp::token_t t({0, 0}, dsp::token_t::identifier, s);
-  dsp::assign_t a(t, l);
+  std::string_view s("-");
+  dsp::token_t t({0, 0}, dsp::token_t::minus, s);
+  dsp::unary_t a(t, &l);
   dsp::ast_printer_t p(std::cout);
   p.visit(&a);
 }
diff --git a/parser.cpp b/parser.cpp
new file mode 100644
index 0000000..41f57dd
--- /dev/null
+++ b/parser.cpp
@@ -0,0 +1,4 @@
+struct parser_t
+{
+
+}
diff --git a/stmt.hpp b/stmt.hpp
new file mode 100644
index 0000000..5a23fb4
--- /dev/null
+++ b/stmt.hpp
@@ -0,0 +1,9 @@
+
+struct assign_t : stmt_accept_t<assign_t>
+{
+  assign_t(token_t name, expr_t * value)
+    : name(name), value(value) {}
+
+  const token_t name;
+  const expr_t * value;
+};
diff --git a/visitable.hpp b/visitable.hpp
index 2da8c02..6ab5880 100644
--- a/visitable.hpp
+++ b/visitable.hpp
@@ -2,7 +2,10 @@
 
 namespace dsp {
 
-struct assign_t;
+struct binary_t;
+struct grouping_t;
 struct literal_t;
+struct unary_t;
+struct assign_t;
 
 }
diff --git a/visitor.hpp b/visitor.hpp
index 55b2175..6bcf7e1 100644
--- a/visitor.hpp
+++ b/visitor.hpp
@@ -8,7 +8,9 @@ namespace dsp {
 template <typename T>
 struct visitor_t
 {
-  virtual T visit(const assign_t * expr) const = 0;
+  virtual T visit(const unary_t * expr) const = 0;
+  virtual T visit(const binary_t * expr) const = 0;
+  virtual T visit(const grouping_t * expr) const = 0;
   virtual T visit(const literal_t * expr) const = 0;
 };